Patent Publication Number: US-6699123-B2

Title: Entertainment system, entertainment apparatus, recording medium, and program

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation-in-part of U.S. patent application Ser. No. 09/687,577 filed on Oct. 13, 2000, which is assigned to the assignee of the present application. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an entertainment system, an entertainment apparatus, a recording medium, and a program for displaying a novel line drawing image according to music on a display screen to allow a game to be played. 
     2. Description of the Related Art 
     In some information apparatuses such as entertainment apparatuses including video game machines (entertainment systems), for example, a game is played by manipulating a controller while displaying the contents of the game stored in a recording medium such as a CD-ROM on the screen of a television receiver as a monitor. 
     Currently, many games available on the market are directed to utilize more realistic and finer video images with the aid of recent advanced technology. In such games, the controller of the entertainment apparatus can be vibrated according to the movement of images so as to make the games more realistic and interesting. Under the circumstances, since games are getting more complicated, the difficulties of the games tend to be increased. In some games, high level of skills for manipulating the controller is required for the user. In this case, it is not possible for some users such as amateur game players or older people to complete the games. Further, once a user completes such games and acquires the manipulation skills, the user may soon get tired of playing the games. 
     In contrast, less complicated games utilizing only line drawing images can be widely accepted by people in different generations. That is, since such games are simple and do not require manipulation skills, children and old people can enjoy the heartwarming games. 
     SUMMARY OF THE INVENTION 
     The present invention was made taking the above-described points into consideration, and an object of the invention is to provide an entertainment system, an entertainment apparatus, a recording medium, and a program for displaying a novel line drawing image on a display screen to allow a game to be played. 
     Specifically, the object of the invention is to provide an entertainment system, an entertainment apparatus, a recording medium, and a program for displaying a novel line drawing image according to music on a display screen to allow a highly entertaining game to be played. 
     An entertainment system of the present invention comprises: 
     an entertainment apparatus for executing various programs; 
     a manual controller for inputting a manual control request of a user to the entertainment apparatus; and 
     a display monitor for displaying an image outputted from the entertainment apparatus, 
     wherein the entertainment apparatus comprises: 
     means for analyzing an audio signal; 
     means for generating at least one substantially linear line drawing image; 
     means for inserting a non-linear line drawing portion based on an result of an analysis of the audio signal into the substantially linear line drawing image to generate a modified substantially linear line drawing image having the non-linear line drawing portion; and 
     means for generating a line drawing image of a character object; 
     wherein the line drawing image of the character object is displayed on the modified substantially linear line drawing image having the non-linear line drawing portion on the display monitor. 
     According to the entertainment system of the present invention, a line drawing image of a character object is generated on a modified substantially linear line drawing image having a non-linear line drawing image portion which has been inserted based on a result of analysis of an audio signal. This makes it possible to display a novel line drawing image according to music on the display. 
     In this case, two modified substantially linear line drawing images each having a non-linear line drawing image portion are generated. Then, a character line drawing image is generated on each of the modified substantially linear line drawing images. Accordingly, it is possible for two users to play a match game (competition game). 
     In the above entertainment system according to the present invention, the entertainment apparatus may further comprise means for moving the line drawing image of the character object relative to the modified substantially linear line drawing image having the non-linear line drawing portion. Accordingly, it is possible to generate a more entertaining line drawing image. 
     Further, the entertainment apparatus may further comprise means for changing the line drawing image of the character object into a line drawing image of a different character object depending on how the line drawing image of the character object moves on the modified substantially linear line drawing image having the non-linear line drawing portion. Accordingly, it is possible to generate a still more entertaining line drawing image. 
     Further, the entertainment apparatus may comprise means for imparting vibrations to the modified substantially linear line drawing image having the non-linear line drawing portion and the line drawing image of the character object. Accordingly, it is possible to generate a quite entertaining line drawing image. 
     In this case, each of the line drawing images may be drawn as a three-dimensional line drawing image to generate a highly entertaining image which is less likely to become tiresome. 
     Further, an audio signal may be used which is supplied to the entertainment apparatus from a recording medium or which is downloaded thereto via communication. 
     An entertainment apparatus of the present invention is connectable to a manual controller for inputting a manual control request of a user to the entertainment apparatus, and connectable to a display monitor for displaying an image outputted from the entertainment apparatus, 
     wherein the entertainment apparatus comprises: 
     means for analyzing an audio signal; 
     means for generating at least one substantially linear line drawing image; 
     means for inserting a non-linear line drawing portion based on a result of an analysis of the audio signal into the substantially linear line drawing image to generate a modified substantially linear line drawing image having the non-linear line drawing portion; and 
     means for generating a line drawing image of a character object; 
     wherein the line drawing image of the character object is displayed on the modified substantially linear line drawing image having the non-linear line drawing portion on the display monitor. 
     According to the entertainment apparatus of the present invention, a line drawing image of a character object is generated on a modified substantially linear line drawing image having a non-linear line drawing image portion which has been inserted based on a result of analysis of an audio signal. This makes it possible to display a novel line drawing image according to music on the display. 
     In this case, two modified substantially linear line drawing images each having a non-linear line drawing image portion are generated. Then, a character line drawing image is generated on each of the modified substantially linear line drawing images. Accordingly, it is possible for two users to play a match game (competition game). 
     A recording medium of the present invention comprises the steps of: 
     analyzing an audio signal; 
     generating at least one substantially linear line drawing image; 
     inserting a non-linear line drawing portion based on a result of an analysis of the audio signal into the substantially linear line drawing image to generate a modified substantially linear line drawing image having the non-linear line drawing portion; and 
     generating a line drawing image of a character object on the modified substantially linear line drawing image having the non-linear line drawing portion. 
     According to the recording medium of the present invention, a line drawing image of a character object is generated on a modified substantially linear line drawing image having a non-linear line drawing image portion which has been inserted based on a result of analysis of an audio signal. This makes it possible to display a novel line drawing image according to music on the display. 
     In this case, two modified substantially linear line drawing images each having a non-linear line drawing image portion are generated. Then, a character line drawing image is generated on each of the modified substantially linear line drawing images. Accordingly, it is possible for two users to play a match game (competition game). 
     The recording medium is applicable to a recording medium for recording programs and data used for an entertainment system comprising: 
     an entertainment apparatus for executing various programs; 
     a manual controller for inputting a manual control request of a user to the entertainment apparatus; and 
     a display monitor for displaying an image outputted from the entertainment apparatus. 
     In the above recording medium of the present invention, the program may further comprise the step of moving the line drawing image of the character object relative to the modified substantially linear line drawing image having the non-linear line drawing portion. Accordingly, it is possible to generate a more entertaining line drawing image. 
     Further, the program may further comprise the step of changing the line drawing image of the character object into a line drawing image of a different character object depending on how the line drawing image of the character object moves on the modified substantially linear line drawing image having the non-linear line drawing portion. Accordingly, it is possible to generate a still more entertaining line drawing image. 
     Further, the program may further comprise the step of imparting vibrations to the modified substantially linear line drawing image having the non-linear line drawing image portion and the line drawing image of the character object. Accordingly, it is possible to generate a quite entertaining line drawing image. 
     In this case, each of the line drawing images may be drawn as a three-dimensional line drawing image to generate a highly entertaining image which is less likely to become tiresome. 
     A program of the present invention comprises the steps of: 
     analyzing an audio signal; 
     generating at least one substantially linear line drawing image; 
     inserting a non-linear line drawing portion based on a result of an analysis of the audio signal into the substantially linear line drawing image to generate a modified substantially linear line drawing image having the non-linear line drawing portion; and 
     generating a line drawing image of a character object on the modified substantially linear line drawing image having the non-linear line drawing portion. 
     According to the program of the present invention, a line drawing image of a character object is generated on a modified substantially linear line drawing image having a non-linear line drawing image portion which has been inserted based on a result of analysis of an audio signal. This makes it possible to display a novel line drawing image according to music on the display. 
     In this case, two modified substantially linear line drawing images each having a non-linear line drawing image portion are generated. Then, a character line drawing image is generated on each of the modified substantially linear line drawing images. Accordingly, it is possible for two users to play a match game (competition game). 
     The program is applicable to a program for use of an entertainment system comprising: 
     an entertainment apparatus for executing various programs; 
     a manual controller for inputting a manual control request of a user to the entertainment apparatus; and 
     a display monitor for displaying an image outputted from the entertainment apparatus. 
     The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the invention is shown by way of illustrative example. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an entertainment system according to an embodiment of the present invention. 
     FIG. 2 is a perspective view of a manual controller. 
     FIG. 3 is a block diagram showing a circuit configuration of the entertainment system. 
     FIG. 4 is a block diagram showing a circuit configuration of the manual controller. 
     FIG. 5 is a flow chart for explaining the operation of the entertainment system as a whole. 
     FIG. 6 is an illustration of a game starting screen. 
     FIG. 7 is an illustration of a name registration screen. 
     FIG. 8 is an illustration of the name registration screen. 
     FIG. 9 is an illustration of a game selection screen. 
     FIG. 10 is an illustration of the game selection screen. 
     FIG. 11 is a flow chart showing details of game processing. 
     FIG. 12 is an illustration of character objects. 
     FIG. 13 is an illustration of obstacle objects. 
     FIG. 14 is an illustration of a virtual road object. 
     FIG. 15 is an illustration of an example of formation of an object. 
     FIG. 16 is an illustration of a table showing correspondence between control buttons and obstacle objects. 
     FIG. 17 is a flow chart for explaining an audio signal analyzing process. 
     FIG. 18 shows a table of correspondence between results of audio signal analysis and obstacle objects to be generated. 
     FIG. 19 shows a table of correspondence between results of audio signal analysis and obstacle objects to be generated. 
     FIG. 20 is a flow chart for explaining a line drawing display updating process. 
     FIG. 21 is an illustration of a frame buffer. 
     FIG. 22 is an illustration for explaining generation of a three-dimensional line drawing image. 
     FIG. 23 is an illustration of a screen that appears immediately after the beginning of a game. 
     FIG. 24 is an illustration for explaining a vibration process. 
     FIG. 25 is an illustration showing a screen that appears several seconds after the beginning of the game. 
     FIG. 26 is an illustration of a screen in which a character object gets over an obstacle object. 
     FIG. 27 is an illustration of a screen in which the character object rolls over an obstacle object. 
     FIG. 28 is an illustration of a screen in which the character object strides over an obstacle object. 
     FIG. 29 is an illustration of a screen in which the character object rolls in an obstacle object. 
     FIG. 30 is an illustration of a screen which appears immediately after the character object fails in getting over an obstacle object. 
     FIG. 31 is an illustration of a screen which appears at a time interval of about one second or more after the character object fails in getting over the obstacle object. 
     FIG. 32 shows a table of character status. 
     FIG. 33 is an illustration of a Game Over screen. 
     FIG. 34 is an illustration of the Game Over screen. 
     FIG. 35 is an illustration of an Ending screen. 
     FIG. 36 is a block diagram showing an image processing/audio processing function. 
     FIG. 37 is an illustration for explaining an example of a screen according to an embodiment of a game for two players. 
     FIG. 38 is an illustration for explaining another example of a screen according to the embodiment of a game for two players. 
     FIG. 39 is an illustration for explaining still another example of a screen according to the embodiment of a game for two players. 
     FIG. 40 shows an example of a table of correspondence between control buttons and obstacle objects according to another embodiment of the invention. 
     FIG. 41 is an illustration for explaining creation of an obstacle object according to the embodiment. 
     FIG. 42 is an illustration for explaining obstacle objects according to the embodiment. 
     FIG. 43 is an illustration of a screen in which obstacle objects rotate about a virtual road. 
     FIG. 44 is a view showing a waveform of a digital audio signal. 
     FIG. 45 is a view showing distinctive points in the waveform of the digital audio signal. 
     FIG. 46 is a view showing a waveform of an emphasized signal generated by emphasizing the digital audio signal in a predetermined process. 
     FIG. 47 is a view showing a waveform of a signal (attack events) generated by converting the emphasized signal with a threshold to eliminate unnecessary parts of the waveform. 
     FIG. 48 is a view showing peaks of the respective attack events (potential events) in the waveform. 
     FIG. 49 is a view showing final events selected from the potential events in the waveform by a predetermined process. 
     FIG. 50 is a view showing positions of the final events in the waveform of the digital audio signal. 
     FIG. 51 is a view partially showing the waveform in FIG. 41 which is enlarged on the time axis. 
     FIG. 52 is a view illustrating a power of an audio event at a certain time point. 
     FIG. 53 is a graph showing short term powers. 
     FIG. 54 is a graph showing the short term powers and long term powers. 
     FIG. 55 is a view showing the waveform of the emphasized signal as the ration of the short term power to the long term power. 
     FIG. 56 is a view showing attack events in the waveform which is divided into select periods. 
     FIG. 57 is a view showing potential events representing peaks in respective select periods of the waveform. 
     FIG. 58 is a view showing the waveform of potential events in which shadow periods are set on the time axis of the waveform. 
     FIG. 59 is a view showing final events in the waveform. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the present invention will be described below specifically with reference to drawings. 
     FIG. 1 shows generally an arrangement of an entertainment system  10  to which an image processing apparatus according to the embodiment of the present invention is applied. 
     The entertainment system  10  basically comprises an entertainment apparatus  12  for executing various programs, a memory card  14  detachably connected to the entertainment apparatus  12 , a manual controller  16  detachably connected to the entertainment apparatus  12  by a connector  62 , and a monitor  18  such as a television receiver which is supplied with video and audio output signals from the entertainment apparatus  12 . 
     The entertainment apparatus  12  reads a program and data recorded in a mass storage medium such as an optical disk  20  such as a CD-ROM or the like, and executes a game, for example, based on the program depending on commands supplied from a user, e.g., a game player, via the manual controller  16 . The execution of the game mainly represents controlling the progress of the game by controlling the display of images and the generation of sounds on the monitor  18  based on manual input actions entered from the manual controller  16  via the connector  62 . 
     The entertainment system  12  is capable of playing back an optical disk  20  such as a CD (compact disk) as a recording medium. Specifically, audio signals as music data (sound data) are read and played back by referring TOC (table of contents) data stored in the compact disk. 
     Further, the entertainment apparatus  12  is capable of executing a game program by utilizing the TOC data and music data stored in the compact disk. 
     The recording medium for supplying the application program and sound data is not limited to the optical disk  20 . Alternatively, the entertainment apparatus  12  may be supplied with the application program and sound data via a communication link, rather than being supplied from the optical disk  20  as the recording medium. 
     The entertainment apparatus  12  has a substantially flat casing in the shape of a rectangular parallelepiped which houses a disk loading unit  22  disposed centrally for loading the optical disk  20  for supplying the application program and data for a video game or the like. The casing supports a reset switch  24  for resetting a program which is being presently executed, a disk control switch  26  for controlling the loading of the optical disk  20 , a power supply switch  28 , and two slots  30 ,  32 . 
     The slots  30 ,  32  have respective upper slot units  30 B,  32 B and respective lower slot units  30 A,  32 A. Two manual controllers  16  may be connected respectively to the lower slot units  30 A,  32 A via the connectors  62 , and memory cards  14  for storing flags indicative of interim game data may be connected respectively to the upper slot units  30 B,  32 B. 
     As shown in FIG. 1, when two manual controllers  16  connected to the slot units  30 A,  32 A via the connectors  62 , two users can play a match game (competition game). 
     The match game (competition game) may be played by more than two game players. In this case, a conventional multi-tap adapter (not shown) is connected to the slot unit  30 A. The multi-tap adapter is provided with more than two slots having the shape of the slot unit  30 A. Then, manual controllers  16  are connected to the slot units of the multi-tap adapter. In this manner, more than two manual controllers  16  can be connected to the entertainment apparatus  12  via the multi-tap adapter. 
     The slots  30 ,  32  (the upper slot units  30 B,  32 B and the lower slot units  30 A,  32 A) are asymmetrically shaped to prevent the connectors  62  and the memory cards  14  from being inserted in the wrong direction. 
     As shown in FIGS. 1 and 2, the manual controller  16  basically comprises first and second control pads  34 ,  36 , an L (Left) button  38 L, an R (Right) button  38 R, a start button  40 , and a selection button  42 . The manual controller  16  also has joysticks  44 ,  46  for making analog control actions, a mode selection switch  48  for selecting control modes of the joysticks  44 ,  46 , and an indicator  50  for indicating a selected control mode. The indicator  50  comprises a light-emitting element such as a light-emitting diode or the like. 
     As shown in FIG. 2, the manual controller  16  has a housing  104  comprising an upper member  100  and a lower member  102  which are mated and joined to each other by fasteners such as screws. 
     As shown in FIG. 2, a pair of left and right grips  106 ,  108  projects from one side of respective opposite ends of the housing  104 . The left and right grips  106 ,  108  are shaped so as to be gripped by the palms of left and right hands of the user or game player when the manual controller  16  is connected to the entertainment apparatus  12  and information retrieval is carried out or the game is played thereby, for example. 
     As shown in FIG. 1, the left and right grips  106 ,  108  are progressively spaced away from each other toward their distal ends. 
     As shown in FIGS. 2, the first control pad  34  is disposed on one end of the housing  104  and comprises a first pressable control member (up button)  110   a , a second pressable control member (right button)  110   b , a third pressable control member (down button)  110   c , and a fourth pressable control member (right button)  110   d . The first through fourth pressable control members  110   a ,  110   b ,  110   c ,  110   d  project on an upper surface of the housing  104  and are arranged in a crisscross pattern. 
     The first control pad  34  includes switch elements as signal input elements associated respectively with the first through fourth pressable control members  110   a ,  110   b ,  110   c ,  110   d . The first control pad  34  functions as a directional controller for controlling the direction of movement of a displayed game character, for example. When the game player selectively presses the first through fourth pressable control members  110   a ,  110   b ,  110   c ,  110   d  to turn on or off the switch elements associated respectively with the first through fourth pressable control members  110   a ,  110   b ,  110   c ,  110   d , the displayed game character moves in the direction corresponding to the pressed one of the first through fourth pressable control members  110   a ,  110   b ,  110   c ,  110   d.    
     As shown in FIGS. 1 and 2, the second control pad  36  is disposed on the other end of the housing  104  and comprises a first pressable control member (Δ button)  112   a , a second pressable control member (◯ button)  112   b , a third pressable control member (X button)  112   c , and a fourth pressable control member (□ button)  112   d . The first through fourth pressable control members  112   a ,  112   b ,  112   c ,  112   d  project on the upper surface of the housing  104  and are arranged in a crisscross pattern. 
     The first through fourth pressable control members  112   a ,  112   b ,  112   c ,  112   d  are constructed as independent members, and associated with respective switch elements disposed in the second control pad  36 . 
     The second control pad  36  serves as a function setting/performing unit for setting functions for a displayed game character assigned to the pressable control members  112   a - 112   d  or performing functions of a displayed game character when the switch elements associated with the pressable control members  112   a - 112   d  are turned on. 
     The L button  38 L and the R button  38 R are disposed on a side of the housing  104  remote from the first and second grips  106 ,  108  and positioned respectively at the opposite ends of the housing  104 . As shown in FIG. 2, the L button  38 L and the R button  38 R have respective first and second pressable control members  114   a ,  114   b  and  116   a ,  116   b  and respective switch elements associated respectively with the pressable control members  114   a ,  114   b  and  116   a ,  116   b.    
     The L button  38 L and the R button  38 R serve as respective function setting/performing units for setting functions for a displayed game character assigned to the pressable control members  114   a ,  114   b  and  116   a ,  116   b  or performing functions of a displayed game character when the switch elements associated with the pressable control members  114   a ,  114   b  and  116   a ,  116   b  are turned on. 
     The first pressable control members  114   a ,  114   b  are also referred to as the L 1  button  114   a , the L 2  button  114   b , respectively. The second pressable control members  116   a ,  116   b  are also referred to as the R 1  button  116   a , the R 2  button  114   b , respectively. 
     As shown in FIG. 2, the manual controller  16  also has left and right analog control pads  118 ,  120  disposed respectively at confronting corners defined between the housing  104  and the proximal ends of the first and second grips  106 ,  108  which are joined to the housing  104 . 
     The left and right analog control pads  118 ,  120  have the respective joysticks  44 ,  46  which can be tilted in all directions 360° about control shafts thereof, and respective signal input elements such as variable resistors or the like which are operable by the respective joysticks  44 ,  46 . Specifically, the joysticks  44 ,  46  are mounted on tip ends of the control shafts that are normally urged to return to their neutral positions by resilient members, and can be tilted in all directions (360°) about the axes of the control shafts. 
     The left and right analog control pads  118 ,  120  can move a displayed game character while rotating the same or while changing its speed, and can make an analog-like action such as to change the form of a displayed character, when the game player rotates the joysticks  44 ,  46 . Therefore, the left and right analog control pads  118 ,  120  are used as a control unit for entering command signals for a displayed character to perform the above movement or action. 
     When the mode selection switch  48  is pressed, it can select a control mode for allowing a command signal to be inputted from the left and right analog control pads  118 ,  120  or a control mode for inhibiting a command signal from being inputted from the left and right analog control pads  118 ,  120 . 
     When the mode selection switch  48  is pressed, it can also select a control mode for allowing a command signal to be inputted from the left and right analog control pads  118 ,  120  and selecting the function of the first through fourth pressable control members  112   a ,  112   b ,  112   c ,  112   d  of the second control pad  36  or the function of the pressable control members  114   a ,  114   b  and  116   a ,  116   b  of the L button  38 L and the R button  38 R. Depending on the control mode selected by the mode selection switch  48 , the mode indicator  50  flickers and changes its indication light. 
     As shown in FIG. 2, the first and second grips  106 ,  108  projecting from the housing  104  are gripped respectively by the palms of the hands of the game player. The housing  104  is not required to be supported by fingers, and the manual controller  16  can be held by the hands while at least six out of the ten fingers of the hands can freely be moved. 
     As shown in FIG. 2, when the first and second grips  106 ,  108  are gripped respectively by the palms of the hands of the game player, the thumbs Rf 1 , Lf 1  of the right and left hands can extend over the joysticks  44 ,  46  of the left and right analog control pads  118 ,  120 , the first through fourth pressable control members  110   a - 110   d  of the first control pad  34 , and the first through fourth pressable control members  112   a - 112   d  of the second control pad  36 , and can selectively press the joysticks  44 ,  46 , the pressable control members  110   a - 110   d , and the pressable control members  112   a - 112   d.    
     Since the joysticks  44 ,  46  of the left and right analog control pads  118 ,  120  are positioned in confronting relation to the proximal ends of the first and second grips  106 ,  108  which are joined to the housing  104 , when the first and second grips  106 ,  108  are gripped by the left and right hands, the joysticks  44 ,  46  are positioned most closely to the thumbs Rf 1 , Lf 1 , respectively. Therefore, the joysticks  44 ,  46  can easily be rotated by the thumbs Rf 1 , Lf 1 . 
     As shown in FIG. 2, when the first and second grips  106 ,  108  are gripped respectively by the palms of the hands of the game player, the index fingers Rf 2 , Lf 2  and middle fingers Rf 3 , Lf 3  of the right and left hands can extend over positions where they can selectively press the first and second pressable control members  114   a ,  114   b  and  116   a ,  116   b  of the R button  38 R and the L button  38 L. 
     Further, the manual controller  16  is provided with unillustrated vibration imparting mechanisms comprising motors or the like for imparting vibrations to the user in order for the user to be able to play a highly realistic game. Vibration commands for energizing the vibration imparting mechanisms are generated by the entertainment apparatus  12  so as to produce suitable vibration effects in the game. 
     Next, circuit arrangements of the entertainment apparatus  12  and the manual controller  16  will be described below. 
     FIG. 3 shows an arrangement of the entertainment system  10  including a circuit arrangement of major electric components of the entertainment apparatus  12 . 
     As shown in FIG. 3, the entertainment apparatus  12  comprises a control system  250  including a central processing unit (CPU)  251  and its peripheral devices, a graphic system  260  including a graphic processing unit (GPU)  262  for generating and storing image data in a frame buffer  263 , a sound system  270  including a sound processing unit (SPU)  271  for generating music sounds and sound effects, an optical disk controller  280  for controlling an optical disk  20  in which application programs are recorded, a communication controller  290  for controlling signals from the manual controller  16  which enter instructions from the user, and data supplied to and from a memory card  14  which stores game settings, and a bus BUS to which the control system  250 , the graphic system  260 , the sound system  270 , the optical disk controller  280 , and the communication controller  290  are connected. 
     The control system  250  comprises a CPU  251 , a peripheral device controller  252  for controlling interrupts and direct memory access (DMA) data transfer, a main memory  253  comprising a random-access memory (RAM), and a read-only memory (ROM)  254  which stores various programs such as an operating system for managing the main memory  253 , the graphic system  260 , the sound system  270 , etc. The main memory  253  is a memory capable of storing a program which is being executed. 
     The CPU  251  controls the entertainment apparatus  12  in its entirety by executing the operating system stored in the ROM  254 . The CPU  251  comprises a 32-bit RISC-CPU, for example. 
     When the entertainment apparatus  12  is turned on, the CPU  251  executes the operating system stored in the ROM  254  to start controlling the graphic system  260 , the sound system  270 , etc. For example, when the operating system is executed, the CPU  251  initializes the entertainment apparatus  12  in its entirety for checking its operation, and thereafter controls the optical disk controller  280  to execute an application program recorded in the optical disk  20  loaded in the disk loading unit  22  (see FIG. 1) 
     As the application program such as a game program stored in the optical disk  20  is executed, the CPU  251  controls the graphic system  260 , the sound system  270 , etc. depending on commands entered from the user for thereby controlling the display of images and the generation of music sounds and sound effects. 
     The graphic system  260  comprises a geometry transfer engine (GTE)  261  for performing coordinate transformations including perspective transformations and other processing, a GPU  262  for generating image data according to instructions from the CPU  251 , a frame buffer  263  for storing image data generated by the GPU  262  and updating a screen image each time a screen switching signal (screen image switching signal) such as a vertical synchronization signal is generated, and an image decoder  264  for decoding image data compressed and encoded by an orthogonal transform such as a discrete cosine transform. The image data stored in the frame buffer  263  is outputted by means of GPU  262  as a video image data. The outputted video image data is supplied to a display  18 A of the monitor  18  such as television receiver or the like via an output terminal. The image data (including three dimensional image data) is updated each time a vertical synchronization signal is generated. 
     The GTE  261  has a parallel arithmetic mechanism for performing a plurality of arithmetic operations parallel to each other, and can perform coordinate transformations (including perspective transformations for transforming three dimensional images into two dimensional images), light source calculations, matrixes, or vectors at a high speed in response to a request from the CPU  251 . Specifically, the GTE  261  can calculate the coordinates of a maximum of 1.5 million polygons per second for a flat shading process to plot one triangular polygon with one color, for example. With the GTE  261 , the entertainment apparatus  12  is able to reduce the burden on the CPU  351  and perform high-speed coordinate calculations. 
     According to an image generating instruction from the CPU  251 , the GPU  262  generates and stores the data of a polygon or the like in the frame buffer  263 . The GPU  262  is capable of generating and storing a maximum of 360 thousand polygons per second. 
     The frame buffer  263  comprises a dual-port RAM, and is capable of simultaneously storing image data generated by the GPU  262  or image data transferred from the main memory  53 , and reading image data for display. 
     The frame buffer  263  has a storage capacity of 1 Mbytes, for example, and is handled as a 16-bit matrix made up of a horizontal row of 1024 pixels and a vertical column of 512 pixels. The frame buffer  263  has areas for selectively storing image data and outputting the stored image data as video output data, a CLUT (color look-up table) area for storing a color look-up table which will be referred to by the GPU  262  when it generates a polygon or the like, and a texture area for storing texture data to be subjected to coordinate transformations when a polygon is generated and mapped onto a polygon generated by the GPU  262 . The CLUT area and the texture area are dynamically varied as the areas for selectively storing image data and outputting the stored image data as video output data are varied. 
     The GPU  262  can perform, in addition to the flat shading process, a Gouraud shading process for determining colors in polygons by interpolating intensities from the vertices of the polygons, and a texture mapping process for mapping textures stored in the texture areas onto polygons. For performing the Gouraud shading process or texture mapping process, the GTE  261  can perform coordinate calculations for a maximum of about 500,000 polygons per second. 
     The image decoder  264  is controlled by the CPU  251  to decode image data of a still or moving image stored in the main memory  253 , and store the decoded image into the main memory  253 . 
     Image data reproduced by the image decoder  264  is transferred to the frame buffer  263  by the GPU  262 , and can be used as a background for an image plotted by the GPU  262 . 
     The sound system  270  comprises an SPU  271  for generating music sounds, sound effects, etc. based on instructions from the CPU  251 , a sound buffer  272  for storing waveform data from the SPU  271 . Music sounds, sound effects generated by the SPU  271  are outputted by a speaker  18 B of the monitor  18 . 
     The SPU  271  has an ADPCM (adaptive differential PCM) function for reproducing 16-bit sound data which has been encoded as 4-bit differential sound data by ADPCM, a reproducing function for reproducing the waveform data stored in the sound buffer  272  to generate sound effects, etc., and a modulating function for modulating and reproducing the waveform data stored in the sound buffer  272 . 
     The sound system  270  can be used as a sampling sound source which generates music sounds, sound effects, etc. based on the waveform data stored in the sound buffer  272  according to commands from the CPU  251 . 
     The optical disk controller  280  comprises an optical disk drive  281  for reproducing application programs and data recorded on the optical disk  20 , a decoder  282  for decoding programs and data that are recorded with an error correcting code (ECC) added thereto, and a buffer  283  for temporarily storing data read from the optical disk drive  281  so as to allow the data from the optical disk  20  to be read at a high speed. An auxiliary CPU  284  is connected to the decoder  282 . 
     Sound data recorded on the optical disk  20  which is read by the optical disk drive  281  includes PCM data converted from analog sound signals, in addition to the ADPCM data. The ADPCM data, which is recorded as 4-bit differential data of 16-bit digital data, is decoded by the decoder  82 , supplied to the SPU  271 , converted thereby into analog data, and applied to drive the speaker  18 B. The PCM data, which is recorded as 16-bit digital data, is decoded by the decoder  282  and then applied to drive the speaker  18 B. 
     The communication controller  290  comprises a communication controller  291  for controlling communication with the CPU  251  via the bus BUS. The communication controller  291  is connected to the manual controller  16  for entering commands from the user, the memory card  14  as an auxiliary memory device for storing game settings, etc. and an unillustrated portable electronic device. 
     As shown in FIGS. 1 and 2, the manual controller  16  has more than 10 command keys for entering commands from the user, and transmits statuses of the command keys about 60 times per second to the communication controller  291  by way of synchronous communication according to an instruction from the communication controller  291 . The communication controller  291  transmits the statuses of the command keys to the CPU  251 . 
     In this manner, commands from the user are applied to the CPU  251 , which carries out a process according to the commands based on the game program being executed. 
     A large amount of image data needs to be transferred at high speed between the main memory  253 , the GPU  262 , the image decoder  264 , and the decoder  282  for reading a program, displaying an image, or generating and storing image data. 
     In the entertainment apparatus  12 , data is transferred directly between the main memory  253 , the GPU  262 , the image decoder  264 , and the decoder  282  according to the DMA data transfer under the control of the peripheral device controller  252 , rather than the CPU  251 . Therefore, the burden on the CPU  251  can be reduced for data transfer, and high-speed data transfer can be achieved between the main memory  253 , the GPU  262 , the image decoder  264 , and the decoder  282 . 
     When setting data of a game being executed need to be stored, the CPU  251  transmits the setting data to the communication controller  291 , which writes the transmitted setting data into the memory card  14  or the unillustrated portable electronic device which is inserted in the slot  30 B,  32 B. 
     The memory card  14  is provided with a main body interface for connection to the entertainment apparatus  12 , and a memory interface for outputting data to and inputting data from a nonvolatile memory incorporated therein. 
     The communication controller  291  (see FIG. 3) has a built-in protection circuit for protection against electric breakdown. The memory card  10  and the portable terminal  100  are separate from the bus BUS, and can be connected and disconnected while the entertainment apparatus  12  is being energized. Therefore, when the memory card  14  suffers a storage capacity shortage, a new memory card can be connected without having to turn off the entertainment apparatus  12 . Consequently, any game data that need to be backed up can be stored in a new memory card  14  connected to the entertainment apparatus  12 , without the danger of being lost. 
     As shown in FIG. 3, the entertainment apparatus  12  further includes a parallel I/O interface (PIO)  296  and a serial I/O interface (SIO)  297  which serve to connect external extended devices to the entertainment apparatus  12 . For example, the parallel I/O interface  296  can be connected to a compact disk player or a DAT (digital audio tape recorder) for playing back music data. The operations (power ON/OFF, music reproduction, stop, skip, and music selection) of the compact disk player and DAT can be controlled by the CPU  251 . The serial I/O interface  297  can be connected to a personal digital assistant such as the unillustrated portable electronic device. 
     The entertainment apparatus  12  is capable of executing a program stored in the optical disk  20  by means of the optical disk drive  281 , while reading digital audio signals from a music player  298  via the PIO  296  simultaneously. 
     As shown in FIG. 4, the bidirectional communication function between the entertainment apparatus  12  and the manual controller  16  can be performed when the connector  62  capable of performing bidirectional serial communications with the manual controller  16  is connected to the entertainment apparatus  12 . 
     A system in the manual controller  16  for performing the bidirectional communication function comprises a serial I/O interface SIO for performing serial communication with the entertainment apparatus  12 , a parallel I/O interface PIO for entering control data from a plurality of control buttons, a one-chip microcomputer comprising a CPU, a RAM, and a ROM, and a motor driver  150  for energizing the motors  130  of the vibration imparting mechanisms. Each of the motors  130  is energized for rotation by a voltage and a current supplied from the motor driver  150 . 
     As described above, the manual controller  16  has more than 10 control buttons PB such as the up button  110   a , the right button  110   b , the left button  110   c , the down button  110   d , the Δ button  112   a , the ◯ button  112   b , the X button  112   c , the □ button  112   d , the L 1  button  114   a , the L 2  button  114   b , the R 1  button  116   a , the R 2  button  116   b.    
     A system in the entertainment apparatus  12  for performing the bidirectional communication function comprises a serial I/O interface SIO for performing serial communication with the manual controller  16 . When the connector  62  is connected to the serial I/O interface SIO of the entertainment apparatus  12 , the serial I/O interface SIO of the entertainment apparatus  12  is connected to the serial I/O interface SIO of the manual controller  16  via the connector  62  for performing bidirectional communications between the manual controller  16  and the entertainment apparatus  12 . Other structural details of the entertainment apparatus  12  are omitted from illustration in FIG.  4 . 
     Signal and control lines for bidirectional serial communications include a data transfer signal line TXD (Transmit X′ for Data) for sending data from the entertainment apparatus  12  to the manual controller  16 , a data transfer signal line RXD (Received X′ for Data) for sending data from the manual controller  16  to the entertainment apparatus  12 , a serial synchronous clock signal line SCK (Ser. Clock) for extracting data from the data transfer signal lines TXD, RXD, a control line DTR (Data Terminal Ready) for establishing and cutting off communication with the manual controller  16  as a terminal, and a flow control line DSR (Data Set Ready) for transferring a large amount of data. 
     The signal and control lines for bidirectional serial communication are accommodated in a cable. As shown in FIG. 4, this cable further includes a power line  152  extending from a power supply in the entertainment apparatus  12  and connected to the motor drivers  150  in the manual controller  16  for supplying electric energy to energize the motors  130  and other components of the manual controller  16 . 
     A process of bidirectional serial communication between the manual controller  16  and the entertainment apparatus  12  will be described below. In order for the entertainment apparatus  12  to communicate with the manual controller  16  to read control data of the control buttons (button information) of the first and second control pads  34 ,  36  and the L button  38 L and the R button  38 R, the entertainment apparatus  12  first outputs selection data to the control line DTR. As a result, the manual controller  16  confirms that it is selected by the control line DTR, and then waits for a signal from the signal line TXD. Then, the entertainment apparatus  12  outputs an identification code indicative of the manual controller  16  to the data transfer signal line TXD. The manual controller  16  receives the identification code from the signal line TXD. 
     When the manual controller  16  recognizes the identification code, the manual controller  16  starts communicating with the entertainment apparatus  12 . The entertainment apparatus  12  sends control data via the data transfer signal line TXD to the manual controller  16 , which sends control data produced by a control button via the data transfer signal line RXD to the entertainment apparatus  12 . In this manner, the entertainment apparatus  12  and the manual controller  16  perform bidirectional serial communications. The bidirectional serial communications will be finished when the entertainment apparatus  12  outputs selection stop data via the control line DTR. 
     With the bidirectional serial communication function, the manual controller  16  can send mainly control data of control buttons PB to the entertainment apparatus  12 , and the entertainment apparatus  12  can send a vibration generating command for energizing the motors  130  of the vibration imparting mechanisms  128  via the data transfer signal line TXD to the manual controller  16 . 
     The vibration generating command for energizing the motors  130  is established in advance in a CD-ROM set in the entertainment apparatus  12 . 
     A description will be made with reference to the flow chart shown in FIG. 5 on functions and operations characteristic of the entertainment system  10  of the present embodiment. 
     First, the monitor  18 , memory card  14  and manual controller  16  are connected to the entertainment apparatus  12 . Further, the optical disk  20  is loaded in the disk loading unit  22 . The optical disk  20  is a recording medium such as a CD-ROM in which various functions are recorded as programs and data. 
     In this state, when the power supply switch  28  is pressed at step S 1 , power is supplied to the entertainment apparatus  12  from an AC power source (not shown). 
     When power is supplied, the CPU  251  starts operating on the operating system stored in the ROM  254  at step S 2  to perform initialization such as writing of required programs and data (including initial screen data and initial music data) read from the ROM  254  in the main memory  253 . 
     At step S 3 , the initial screen data is drawn in the frame buffer  263  through the image decoder  264  and the GPU  262  under the control of the peripheral device controller  252 , and the drawn initial screen data is supplied through the GPU  262  to the display  18 A of the monitor  18  as video output to display an initial screen on the display  18 A. At this time, the initial music data stored in the ROM  254  is supplied to the sound buffer  272  through the SPU  271 , and the stored initial screen data is supplied through the SPU  271  to the speaker  18 B of the monitor  18  as audio output to generate music (pieces of music) from the speaker  18 B in synchronism with the initial screen. 
     Next, at step S 4 , the state of the decoder  282  is checked by, for example, the CPU  251  to confirm the presence of the optical disk  20  in the disk loading unit  22  by checking whether writing of programs and data read from the optical disk drive  281  in the buffer  283  through the decoder  282  has occurred as a result of automatic activation caused by loading of the optical disk  20  which is a CD-ROM. 
     Actually, while the optical disk  20  is not being loaded in the disk loading unit  22 , the display of the initial screen at step S 3  continues. When the optical disk  20  is loaded into the disk loading unit  22 , the process proceeds to the next step S 5 . 
     At the process of step S 5 , the programs and data read from the optical disk  20  are directly stored in the memory  253  through the decoder  282  under the control of the auxiliary CPU  284  or stored in the main memory  253  through the buffer  283 . 
     In the following description, images are processed by CPU  251  or GPU  262 . 
     FIG. 6 shows a start screen  300  displayed on the display  18 A at the process of step S 5 . 
     In the start screen  300 , vibrating images of an alphabetical expression “Vibribbon”, English words “Push Start”, and several asterisks or the like are displayed. Each of these images is a three-dimensional line drawing image having a predetermined length or a three-dimensional image which is separated into parts having predetermined lengths. In this state, for example, the expression “Vibribbon” rotates along a circumferential wall of a virtual transparent column about the axis thereof in the lateral direction of the screen at a predetermined time interval such that the expression “Vibribbon” integrally moves to the further side of the screen and then returns to the front side of the screen. 
     A detailed description will be made later on a process of generating a three-dimensional vibrating line drawing image having a predetermined length or a three-dimensional vibrating line drawing image which is separated into parts having predetermined lengths, the process being a fundamental feature of the display process according to the invention (the process is also referred to as “a three-dimensional line drawing image irregular display process”. 
     When it is determined at step S 6  that the start button  40  of the manual controller  16  has been pressed with the start screen  300  displayed as shown in FIG. 6, a process of registering the name of the user (game player) is performed at step S 7 . 
     At the step S 7 , a name registration process screen  302  as shown in FIG. 7 is displayed on the display  18 A. On the name registration process screen  302 , a presently selected region (see the alphabet “S” in FIG. 7) is enlarged, and each character or symbol is displayed using irregular display of three-dimensional line drawing images. The name of the user, e.g., “POKEPOKE” is then alphabetically input by manipulating the control buttons PB of the manual controller  16 . The control buttons PB are manipulated to move a cursor to the position of “OK” as shown on a display screen  304  in FIG. 8 (the cursor is displayed in a position which is enlarged and displayed using irregular display of three-dimensional line drawing images), and the “◯” button  112   b  is pressed to store (register) the input name in the main memory  253 . 
     At step S 8 , as shown in FIG. 9, a game selection screen  306  for a game selecting process is displayed on the display  18 A. On this screen, a three-dimensional line drawing image is displayed. The three-dimensional line image comprises a decagonal object  308  and names of the selectable types of games or the like positioned on straight lines extending outwardly from vertices of the decagonal object  308 . In this “vibribbon game” (“vibribbon” means a vibrating ribbon), three types (levels) of games at different difficulties such as “easy”, “normal” and “hard” are available, for example. The type of the presently selected game is “easy”. In the vibribbon game, a game character is controlled according to music stored in advance in the optical disk  20 . Specifically, two pieces of music are selectably recorded in the optical disk  20  for each of the three types of games. 
     Further, when an “endless” mode is selected on the game selection screen  306  in FIG. 9, a music CD may be used for such music. In this case, an indication is shown on the display  18 A to notify the user of a need for a music CD. When the user loads a music CD into the disk loading unit  22  instead of a CD-ROM in which programs are stored, pieces of music recorded on the music CD are shuffled to randomly select a piece of music for allowing the user to enjoy the vibribbon game endlessly. The vibribbon game will be described later in detail. 
     Obviously, if a music CD is loaded in the music player  298  in advance, the vibribbon game can be executed when the “endless mode” is selected without removing the optical disk  20  in which the program and data of the vibribbon game are recorded from the disk loading unit  22 . In this case, the real-time characteristics of the game is further improved. Specifically, when a music CD is loaded in the music player  298  in advance, pieces of music recorded on the music CD are shuffled at a point (step) instructed by the program to randomly select a piece of music and the selected piece of music is read and stored into the entertainment apparatus  12  through the music player  298  substantially in real time. 
     Each time either the up button  110   a  or down button  110   d  is pressed when the game selection screen  306  is displayed, the decagonal object  308  and names of selectable game modes or the like are rotated as shown on a game selection screen  310  in FIG. 10 to allow selection of other desired games. In FIG. 9, a “Speed” mode in which music is played at a fast tempo is highlighted. In this state, the user can select the “Speed” mode by pressing the decision button  112   b.    
     When an “Exit” mode is selected on the game selection screen  306  in FIG. 8 or  9 , the process returns to the vibribbon game start screen  300  shown in FIG.  6 . 
     The present embodiment is on an assumption that the ◯ button  112   b  as a decision button is pressed at step S 9  in the state of the game selection screen  306  (see FIG.  9 ). When the decision is made, the vibribbon game in the “easy” mode is started, and a game process at step S 10  is performed. 
     A detailed flow of the game process at step S 10  is shown in FIG.  11 . 
     First, it is checked at step S 21  whether an initial process of a game process as described at the next step S 22  has been carried out or not. 
     In the initial process of the game process at step S 22 , three types of character objects  401 ,  402  and  403  shown in FIG. 12, four types of obstacle objects  411 ,  412 ,  413  and  414  shown in FIG. 13 and a movement path (also referred to as “virtual road”) object  420  shown in FIG. 14 stored in the optical disk  20  are read and stored in the main memory  253  using a world coordinate system. 
     The character objects  401 ,  402  and  403  are modified representations of animals such as a rabbit, a frog and a snake. The obstacle objects  411 ,  412 ,  413  and  414  are modifications of a quadrangle (a square or boxy shape), a circle, a V-shape (an inverted triangle) and a zigzag (a symbol for a resistor), respectively. Further, the virtual road object  420  is a virtual road (a three-dimensional line drawing image) on which the character objects  401 ,  402  and  403  move. The obstacle objects  411 ,  412 ,  413  and  414  generated in accordance with results of sound analysis (audio analysis) as described later are inserted in the virtual road object  420 . 
     In this case, each of the character objects  401 ,  402  and  403 , the obstacle objects  411 ,  412 ,  413  and  414 , and the virtual road object  420  is basically constituted by basic objects  415  as convex shape models (convex polyhedral models) in the form of an elongate rectangular parallelepiped as shown in FIG.  15 . FIG. 15 schematically shows a configuration of the obstacle object  411  as an example. Magnification, reduction, coordinate transform (including movement) and the like on the basic object  415  can be performed by the GTE  261 . 
     As shown in FIG. 15, the polygons that constitute the character objects  401 ,  402  and  403 , the obstacle objects  411 ,  412 ,  413  and  414  and the virtual road object  420  are separated into polygonal components in the form of, for example, a quadrangle (or a triangle) that constitute the basic objects  415 . Those polygons are defined by the three-dimensional coordinates of the vertices thereof and colors of those vertices and are stored in a predetermined area of the main memory  253  (an area for storing the character objects  401 ,  402  and  403 , the obstacle objects  411 ,  412 ,  413  and  414  and the virtual road object  420 ). 
     In the present embodiment, the color is stored as white (for example, the tone values of R (red), G (green) and B (blue) are stored as R (red)=G (green)=B (blue)=255 when the brightness levels are represented by eight bits). Obviously, a different color may be used. 
     Further, in the initial process at step S 22 , a table  416  of correspondence between control buttons PB and the obstacle objects  411 ,  412 ,  413  and  414  (a control buttons/obstacle objects correspondence table) for executing the vibribbon game schematically shown in FIG. 16 is read from the optical disk  20  and stored in a predetermined area of the main memory  253  (a control buttons/obstacle objects correspondence table storing area). 
     As shown in FIG. 16, on the correspondence table  416 , the L 1  button  114   a , R 1  button  116   a , up button  110   a  and Δ button  112   a  are assigned to the obstacle objects  411 ,  412 ,  413  and  414 , respectively. 
     Furthermore, in the initial process at step S 22 , flags as described later (an NG flag F 1  and etc.), a register (character object status register)  456  and the like are set in an initial state (which will be also described later). 
     After the above-described initial process at step S 22  is completed, it is checked whether there is any further music data in the buffer  283  or not in a process at step S 23 . If there is no further music data in the buffer  283 , it is checked whether a game for one piece of music data has been completed or not at step S 24 . If the game for one piece of music data has not been completed, for example, music data for one piece of music in the “easy mode” is read from the optical disk  20  and the read music data is stored in the main memory  253  at step S 25 . Alternatively, the data may be stored in the buffer  283 . 
     In the above-described endless mode, for example, in the process at step S 25 , music data for one piece of music is read from a CD or the like loaded in the music player  298  and the read music data is stored in the main memory  253 . 
     Next, an audio signal analyzing process at step S 26  and a line drawing display updating process at step S 27  are performed in parallel to display a game image on the screen of the display  18 A. 
     FIG. 17 shows a flow chart of the audio signal analyzing process (audio signal analyzing means) at step S 26 . 
     In a process at step S 51 , it is determined whether the music data for a predetermined time of reproduction have been read or not by determining whether the music data is stored in the buffer  283 . 
     If the music data is not stored in the buffer  283 , at step S 52 , the music data for one piece of music is read for the predetermined time from the beginning thereof and is written in the buffer  283 . In the present embodiment, the predetermined time is eight seconds (exactly, eight seconds plus marginal time) that is time required for a relative movement of the virtual road object  420  for a distance of one screen from the upper right side to the lower left side of the screen. 
     A description will now be made on a process of analyzing an audio signal to determine the occurrence of an obstacle object. The music data for eight seconds stored in the buffer  283  (an area for storing music data for the predetermined time) is divided into a predetermined number of parts each of which lasts for a very short period of time (16 parts each of which lasts 0.5 sec. in the present embodiment). 
     In this case, in order to divide an audio signal (also referred to as “music data”) into very small periods of time each of which is 0.5 sec. in the present embodiment, music data for 0.5 sec. is read from the buffer  283  at step S 53 . 
     At step S 54 , a register i is incremented by one (i←i+1) as a counting parameter for the reading operation. 
     The music data for the very short period is sampled at a certain sampling frequency at step S 55 , and a frequency spectrum is extracted at step S 56 . That is, a fast Fourier transform process is performed. The sampling may be followed by a band-pass filtering process in an audio frequency band to eliminate noises. 
     In a process at step S 57 , three (this number of peak values may be appropriately changed) peak values (peak values representing the loudness of sounds) are detected in each of a frequency range equal to or higher than a predetermined frequency fc (this frequency may be varied at random) and a frequency range lower than the same in the extracted frequency spectrum. At step S 58 , the detected peak values in the frequency spectrum are arranged in the order of magnitude in each of the frequency range lower than the predetermined frequency fc and the frequency range equal to or higher than the predetermined frequency fc to determine respective orders of arrangement of the three peak values up to the third peak. 
     For example, assuming that f 11 , f 12  and f 13  represent the three peak frequencies lower than the predetermined frequency fc in an ascending order and that f 4 , f 5  and f 6  represent the three peak frequencies equal to or higher than the predetermined frequency fc in an ascending order. Then, since there are six combinations of peak frequencies in each of the frequency region equal to or higher than fc and the frequency region lower than fc, there are 36 possible orders P of arrangement of peak frequencies in total. 
     At step S 59 , reference is made to a table  428  of correspondence between the peak frequency arranging orders P and the obstacle objects  411 ,  412 ,  413  and  414  (a table of correspondence between results of audio signal analysis and obstacle objects to be generated). At step S 60 , it is decided which of the obstacle objects  411 ,  412 ,  413  and  414  is to be generated based on the present frequency analysis. 
     As shown in FIG. 18, for example, it is decided to generate the obstacle object  411  when the peak frequency arranging order P=[f 11 , f 12 , f 13 , fh 1 , fh 2 , fh 3 ], and it is decided to generate the obstacle object  414  when P=[f 13 , f 12 , f 11 , fh 3 , fh 2 , fh 1 ]. 
     The order of generation of a plurality of obstacle objects may be decided based on a result of one frequency analysis. 
     The audio signal analyzing process at steps S 53  through S 60  is merely an example of an audio signal analyzing process performed using the frequency axis. Alternatively, the audio signal analyzing process can be performed by using the time axis. Specifically, music data may be divided into parts each having a predetermined period of time, e.g., 0.5 sec. Then, peak values of amplitudes of sounds in a divided period of time on the time axis may be extracted in a descending order. Then, gradients Q between adjoining peaks of amplitudes on the time axis may be calculated, and a correspondence table  429  may be provided as permutational combinations of the gradients Q, as shown in FIG.  19 . For example, it is decided to select the obstacle object  411  when a combination of gradients Q between peaks consists of four consecutive positive gradients. 
     In the audio signal analyzing process, the order of appearance of the obstacle objects  411 ,  412 ,  413  and  414  may be determined in advance based on data in a table of contents of a CD (the number of pieces of music, playing times thereof, logical addresses of the pieces of music, etc.) instead of the audio signal itself, for example, in the endless mode. 
     A line drawing display updating process at step S 27  (see FIG. 11) is then performed, and processes at steps S 61  and S 62  are performed in parallel with the line drawing display updating process. The process at step S 61  repeats the processes from steps S 53  to S 60  until the value in the register i associated with the counter parameter set at step S 54  becomes an i-value=16 (a value corresponding to eight sec. period described above). When i=16, the value in the register i associated with the counter parameter is set at an i-value=0 at step S 62 . At this time, all of the music data for eight sec. in the buffer  283  (the area for storing music data for a predetermined time) is read, and the process proceeds to step S 27  (see FIG.  11 ). 
     FIG. 20 is a flow chart of the process of updating line drawing display (including the initial display) at step S 27 . 
     At step S 71 , a single line drawing image in the form of a substantially straight line (which is split straight lines actually) extending from the lower left end to the upper right end of the screen of the display  18 A of the display monitor  18  is generated by the GTE  261  from the virtual road object  420  (see FIG.  14 ). The GPU  262  draws the image in either of drawing regions  265  (i.e., two drawing regions  265 A and  265 B), e.g., the drawing region  265 A in the schematic diagram of the frame buffer  263  shown in FIG.  21 . The frame buffer  263  has a size of 1024 pixels and 512 pixels, for example, in x- and y-directions respectively and functions as a two-buffer having drawing regions  265 A and  265 B each of which is formed by 256 pixels×240 pixels, for example. 
     At step S 72 , as will be described later with reference to a drawing, line drawing images of the obstacle objects  411 ,  412 ,  413  and  414  which are non-linear line drawing images determined based on a result of analysis of an audio signal at step S 58  are similarly drawn in the drawing region  265 A of the frame buffer  263  such that they are inserted in the single substantially linear line drawing image in locations deep in the screen on right side thereof in the order in which they are analyzed. Thus, a linear line drawing image and non-linear line drawing images are synthesized. 
     Further, at step S 73 , a line drawing image of the predetermined character object  401  (see FIG. 12) is similarly drawn in the drawing region  265 A of the frame buffer  263  such that it is drawn on the single substantially linear line drawing image having the non-linear line drawing images in the vicinity of the left end of the screen to be synthesized with the same. The selection of any of the character objects  401 ,  402 ,  403 , etc. is carried out in accordance with the contents of a character object status register  456  which will be described later with reference to FIG.  32 . When the game is started, in the above-described initializing process at step S 22 , data associated with the character object  401  is set as the contents (data) of the character object status register  456 . 
     In the processes at steps S 71 , S 72  and S 73 , drawing is performed by rendering processes on basic objects  415  in the form of an elongate rectangular parallelepiped (see FIG. 15) that respectively constitute the virtual road object  420  comprising the substantially linear line drawing image, the obstacle objects  411 ,  412 ,  413  and  414  comprising non-linear line drawing images and the character object  401  comprising a non-linear line drawing image. The rendering processes include a coordinate transform from the world coordinate system to a camera coordinate system, a perspective transform to transform the coordinate system further into a screen coordinate system, processes on hidden surfaces and coloring processes on the polygons (a scaling process is also performed appropriately). 
     FIG. 22 schematically shows a process performed on the virtual road object  420  constituted by a basic object  415  before it is disposed in a camera coordinate system xyz and in a screen coordinate system xy (an x-y plane). Thus, in the example shown in FIG. 22, a single three-dimensional line drawing image in the form of a straight line is displayed such that it extends from the lower left end on the front side of the screen (x-y plane) of the display  18 A to the upper right end on the further side of the screen. 
     For easier understanding, a description will be made on a three-dimensional image which is displayed on the display  18 A based on drawing data read from the drawing region  265 B in which drawing has been performed in advance, of the drawing regions  265 A and  265 B. 
     FIG. 23 shows a three-dimensional line drawing image  430  which is read from the drawing region  265 B and displayed on the screen of the display  18 A with a coloring process and the like performed thereon by the GPU  262 . 
     The three-dimensional line drawing image  430  is an image in which a character object line drawing image  401 Ia is placed on the left end of a virtual road object line drawing image  420 Ia formed by pieces of line drawing images i.e., vibrating basic objects  415 . The vibrating objects  415  are separate from each other. 
     At step S 74 , the virtual road object line drawing image  420 Ia (a virtual line drawing image having obstacle object line drawing images inserted therein in a case wherein obstacle object line drawing images are present) is drawn such that it moves a predetermined distance in the direction of the arrow E at a predetermined time interval, e.g., each time the screen is updated (every {fraction (1/30)} sec. in the case of an NTSC system). At the same time, components that form the character object line drawing image  401 Ia such as the arms, legs, etc. of a modified rabbit in this case are drawn such that they are alternately moved back and forth to provide an image in which the character object line drawing image  401 Ia seems as if it is in a relative movement (running) in the direction of the arrow F on the screen. 
     The three-dimensional line drawing image  430  shown in FIG. 23 is an image in which only the character object line drawing image  401 Ia and the virtual road object line drawing image  420 Ia are displayed. Line drawing images associated with obstacle objects that are in accordance with results of frequency analysis are displayed based on results of frequency analysis after the three-dimensional line drawing image  430  is displayed. 
     In FIG. 23, a reference numeral  415 I represents a line drawing image of a basic object  415  (a basic object line drawing image). In practice, since a basic object  415  is quite thin, only edge lines of the polygons that constitute the object are drawn in white. 
     Therefore, the three-dimensional line drawing image  430  in the example in FIG. 23 is a quite simple monochromatic image (a monochromatic picture, in practice) in which the background is in black and line drawing portions formed by edge lines of polygons are in white. 
     In the present embodiment, the time required for the right end of the virtual road object line drawing image  420 I to move to the left end of the three-dimensional line drawing image  430  is set at eight sec. as described above. 
     In practice, when an obstacle object line drawing image as described later appears in the virtual road object line drawing image  420 Ia on the screen of the display  18 A of the monitor  18 , the user (game player) can perform operations on the control buttons PB as prescribed in the control buttons/obstacle objects correspondence table  416  in FIG. 16 at predetermined timing according to various elements of music outputted from the speaker  18 B of the monitor  18  or headphones to clear the obstacle object line drawing image. The terms “clear” indicates a state in which the character object line drawing image gets over an obstacle object line drawing image or rolls over the same to move relative to the same at proper timing according to music. When the user fails to perform a prescribed operation on the control buttons PB at predetermined timing to enter a non-clear state, a particular image is generated as described later. The vibribbon game proceeds in such a manner. 
     In the present embodiment, a clear state is determined at step S 74  based on a state of an NG flag F 1  as described later. When the NG flag F 1  is 0 (the clear state), a small vibration imparting process is performed to impart small vibrations (relatively small vibrations) to the next three-dimensional line drawing image to be drawn. When the NG flag F 1  is 1 (the non-clear state or NG state), a big vibration imparting process is performed at step S 77  to impart big vibrations (relatively big vibrations) to the next three-dimensional line drawing image to be drawn. 
     In general, small vibrations give the user (operator) a pleasant feel and a sense of rhythm, and big vibrations give the user (operator) a surprise and the like. The speaker  18 B generates pleasant music with a sense of rhythm synchronously with small vibrations and generates sounds such as loud blasts synchronously with big vibrations. The music may be muted. 
     In this case, the terms “small vibrations” and “big vibrations” represent a difference in the degree of vibrations. In the present embodiment, the term “small vibrations” indicates a level of vibrations (small vibrations) which does not make it difficult for the user to recognize the original shape of an object. The term “big vibrations” indicates a level of vibrations (big vibrations) which makes it difficult for the user to recognize the original shape of an object. 
     When a big vibration imparting process is performed at step S 77 , the NG flag F 1  is reset to F 1 ←0 (F=0) (flag is taken down) at step S 78 . 
     At step S 79 , a new three-dimensional line drawing image which has been subjected to a vibration imparting process (a process of imparting small or big vibrations) is drawn in the drawing region  265 A in which drawing is presently performed instead of the drawing region  265 B which is presently being read for display by a process at step S 78 . 
     The vibration process at steps S 76  and S 77  will now be described. 
     The vibration process is a process in which after a random number is added to each of the vertices of the polygons that form each of basic objects  415  which are pieces of line drawing images forming all objects provided in a three-dimensional space, images constituted by only edge lines of the polygons are drawn again. 
     In a mathematical description, relatively small random numbers RDS are generated for the small vibration process, and relatively big random numbers RDB are generated for the big vibration process. When the NG flag F 1  is 0, relatively small random numbers RDS (Δxs, Δys, Δzs) are added to the coordinates (x, y, z) of the respective vertices of a basic object  415  to transform the vertex coordinates into vertex coordinates (x+Δxs, y+Δys, z+Δzs), and straight lines are drawn between the transformed vertex coordinates to define the edge lines of a new polygon. 
     When the NG flag F 1  is 1, relatively big random numbers RDB (Δxb, Δyb, Δzb) are added to the coordinates (x, y, z) of the respective vertices to transform the vertex coordinates into vertex coordinates (x+Δxb, y+Δyb, z+Δzb), and straight lines are drawn between the transformed vertex coordinates to define the edge lines of a new polygon. 
     Referring now to FIG. 24 for a graphical description, the small vibration process creates a basic object  415   a  by slightly moving (i.e., rotating, enlarging or displacing) a basic object  415  which is initially drawn in a quantity represented by the arrows SV and SV′ in the three-dimensional space, and the big vibration process creates a basic object  415   b  by moving the basic object  415  in a larger quantity represented by the arrows LV and LV′ in the three-dimensional space. 
     At step S 77 , the three-dimensional object to which vibrations have been imparted is drawn in the drawing region  265  ( 265 A or  265 B) in which no drawing is presently performed. When it is drawn in the drawing region  265 , since no texture is applied to the surfaces of the polygon that constitutes the basic object  415 , no change occurs in the quality and the feel of the material of the basic object  415  even if it is enlarged or reduced. In other words, an advantage is achieved in that the simplicity of the image is not deteriorated even if it is enlarged or reduced. 
     The three-dimensional line drawing image  430  shown in FIG. 23 is an image in which small vibrations are imparted to each of the basic object line drawing images  415 Ia. 
     At step S 79 , the three-dimensional line drawing image to which vibrations have been imparted is drawn in the drawing region  265 B which is not presently being displayed. At step S 80 , display is presented from the drawing region  265 A in which drawing has already been completed. As described above, the display process at step S 80  and other processes are performed in parallel. The other processes indicate processes at step S 26  (steps S 51  through S 60 ) and at steps S 71  through S 79  and processes from step S 28  through step S 23  up to step S 26 . 
     For convenience in understanding, a description will now be made with reference to FIGS. 25 through 32 on a three-dimensional line drawing image displayed on the screen of the display  18 A and the progress of a game. 
     FIG. 25 shows a three-dimensional line drawing image  432  having small vibrations imparted thereto which is obtained after the game process flow at step S 10  shown in FIG. 11 is repeated for several seconds. 
     While separate pieces of line drawing images that form a game character represent the character as if it is running in the three-dimensional line drawing image  432 , the entire image is presented as an image in which an obstacle object line drawing image  411 Ib, an obstacle object line drawing image  414 Ib and an obstacle object line drawing image  412 Ib inserted in a virtual road object line drawing image  420 Ib are sequentially moved from the further right side of the screen to the front left side of the screen (in the direction of the arrow E) relative to a character object line drawing image  401 Ib which is relatively stationary in the vicinity of the left end of the screen. 
     Specifically, in the three-dimensional line drawing image  432 , figuratively speaking, a rabbit (the character object line drawing image  401 Ib) seems as if it is running while moving up and down at the positions of a quadrangular obstacle object (the obstacle object line drawing image  411 Ib), a zigzag obstacle object (the obstacle object line drawing image  414 Ib), a V-shaped obstacle object (the obstacle object line drawing image  414 Ib) and a circular obstacle object (the obstacle object line drawing image  412 Ib) which are moving toward the rabbit. 
     In a three-dimensional line drawing image  434  shown in FIG. 26, when the L 1  button  114   a  is pressed at predetermined timing (in a predetermined range) in response to a movement of an obstacle object line drawing image  411 Ic toward the front left end of the screen and a resultant increase in the size of its quadrangular configuration, a character object line drawing image  401 Ic gets over the quadrangular obstacle object line drawing image  411 Ic in a manner like leapfrog. Thus, the quadrangular obstacle object line drawing image  411 Ic can be cleared. 
     At this time, a virtual road object line drawing image  420 Ic, an obstacle object line drawing image  414 Ic, an obstacle object line drawing image  413 Ic and an obstacle object line drawing image  412 Ic also move in the direction of the arrow E while gradually increasing in size. 
     In a three-dimensional line drawing image  436  shown in FIG. 27, when the Δ button  112   a  is pressed at predetermined timing (in a predetermined range) in response to a movement of an obstacle object line drawing image  414 Id toward the front left end of the screen and a resultant increase in the size of its zigzag configuration, a character object line drawing image  401 Id moves over the zigzag obstacle object line drawing image  414 Id by making a so-called forward roll on the same. Thus, the zigzag obstacle object line drawing image  414 Id can be cleared. 
     At this time, a virtual road object line drawing image  420 Id, an obstacle object line drawing image  413 Id and an obstacle object line drawing image  412 Id also move in the direction of the arrow E while gradually increasing in size. 
     In a three-dimensional line drawing image  438  shown in FIG. 28, when the up button  110   a  is pressed at predetermined timing (in a predetermined range) in response to a movement of an obstacle object line drawing image  413 Ie toward the front left end of the screen and a resultant increase in the size of its V-shaped configuration, a character object line drawing image  401 Ie moves over the V-shaped obstacle object line drawing image  413 Ie in such a matter that it strides over the same. Thus, the V-shaped obstacle object line drawing image  413 Ie can be cleared. 
     At this time, a virtual road object line drawing image  420 Ie and an obstacle object line drawing image  412 Ie also move in the direction of the arrow E while gradually increasing in size. 
     In the three-dimensional line drawing image  438 , a new obstacle object line drawing image  414 Ie which is generated as a result of an audio signal analyzing process performed concurrently with the display process is drawn on the right end of the virtual road object line drawing image  420 Ie. 
     In a three-dimensional line drawing image  440  shown in FIG. 29, when the R 1  button  116   a  is pressed at predetermined timing (in a predetermined range) in response to a movement of an obstacle object line drawing image  412 If toward the front left end of the screen and a resultant increase in the size of its circular configuration, a character object line drawing image  401 If moves in the circular obstacle object line drawing image  412 If in such a manner that it seems like walking. Thus, the circular obstacle object line drawing image  412 If can be cleared. 
     At this time, a virtual road object line drawing image  420 If, an obstacle object line drawing image  414 If and a newly generated obstacle object line drawing image  413 If also move in the direction of the arrow E while gradually increasing in size. 
     FIGS. 26 through 29 show line drawing images in which the character object  401  clears the obstacle objects  411 ,  412 ,  413  and  414 , respectively. 
     FIG. 30 shows a three-dimensional line drawing image  450  that appears immediately after a so-called non-clear state which occurs when the L 1  button  114   a  is not pressed at the predetermined timing (in the predetermined range) relative to the obstacle object line drawing image  411   b  in the display of the three-dimensional line drawing image  432  shown in FIG. 25 or when a control button PB other than the L 1  button  114   a  is pressed even though at the predetermined timing (in the predetermined range). 
     As shown in FIG. 30, big vibrations (explosive vibrations) described in the process at step S 77  are imparted to each of basic object line drawing images  415 Ig that form an obstacle object line drawing image  411 Ig to display it as an image of broken pieces. Such big vibrations also affect a character object line drawing image  401 Ig and a virtual road object line drawing image  420 Ig in the vicinity of the same. As shown in FIG. 30, this results in an image in which relatively big vibrations are imparted also to basic object line drawing images  401 Ig that form the character object line drawing image  401 Ig and virtual road object line drawing image  420 Ig, although the vibrations are still categorized as small vibrations according to the process at step S 76 . 
     At this time, vibrations may be imparted to the joysticks  44  and  46  through the motor driver  150  and motor  130 . 
     The three-dimensional line drawing image  450  including the broken object shown in FIG. 30 clearly indicates that the user could not clear the obstacle object line drawing image  411 Ig (the non-clear or NG state). 
     FIG. 31 shows a three-dimensional line drawing image  452  that appears within a predetermined time (e.g., within one second) after a failure in clearing the obstacle object line drawing image  411 Ig. 
     As shown in FIG. 31, when the obstacle object line drawing image  411 Ib (or any one of the other obstacle object line drawing images  414 Ib,  413 Ib and  412 Ib) shown in FIG. 25 was not cleared, an image appears in which vibrations have been imparted to enhance small vibrations slightly. Further, in such a non-clear state, the moving speed of the virtual road object line drawing image  420 Ig in the direction of the arrow E may be increased to reduce predetermined timing (a predetermined range) that allow a character object  401 Ih to clear an obstacle object  414 Ih, thereby increasing the difficulty of the game. 
     FIG. 32 is a character status table  454  showing changes in the statuses (metaphorically speaking, degeneration and evolution) of the character objects  401 ,  402  and  403  shown in FIG. 12 in the “easy” mode. 
     As shown in the character status table  454 , the character object that appears first (at the time when the game is started) in the “easy mode” of the vibribbon game is the character object  401  which is a modification of a rabbit and to which very slight vibrations (small vibrations at step S 76 ) are imparted. When the character object  401  fails to clear any one of the obstacle objects  411 ,  412 ,  413  and  414 , the above-described big vibrations are imparted to the character object to break up the same, and a character object  401 ′ having slightly bigger vibrations appears thereafter. 
     When the character object  401 ′ having bigger vibrations (vibrations that still leave the original shape as described at step S 76 ) fails to clear an obstacle object again, the above-described big vibrations are imparted to break up the same and to cause it to change (transform itself) into a character object  402  which is a modification of a frog and to which very small vibrations are imparted. 
     When failures in clearing are similarly repeated, the change of the character object is repeated. Specifically, the above-described big vibrations are imparted to break up the character object  402  to change it into a character object  402 ′ to which slightly bigger vibrations are imparted. Then, the character object  402 ′ is caused to transform itself into a character object  403  which is a modification of a snake and to which still smaller vibrations are imparted. Thereafter, the character object  403  is changed to a character object  403 ′ to which slightly bigger vibrations are imparted. In this manner, each time the character object fails in clearing an obstacle object, the appearance of the character object gets miserable. In the end, when the obstacle objects  411 ,  412 ,  413  and  414  can not be cleared over a predetermined number of trials, that is, when the character object fails in clearing an obstacle object after the character object is changed to the character object  403 ′, the game is terminated, i.e., the game is over. 
     Even when the character object  401  once changes (degenerates) in the direction of the arrow B, i.e., when the character object  401  sequentially changes to the character objects  401 ′,  402 ,  402 ′,  403  and  403 ′, changes in the direction of the arrow F that is opposite to the direction of the arrow B (evolution) occurs if the clear state consecutively occurs or the probability of clearance increases thereafter. For example, re-transformation from the character object  403  into the character object  402 ′ and the like can occur. 
     Algorithm for defining what state of clearance triggers a transformation and so on is determined in advance for each of the game modes, and the number and pattern of such clear states are prescribed in the relevant program. 
     When a piece of music is terminated while the character object is in any of the states represented by  401 ,  401 ′,  402 ,  402 ′,  403  and  403 ′, the game mode is terminated in a clear state, and a point is displayed in accordance with the states of clearance of the obstacle objects  411 ,  412 ,  413  and  414  at that time. 
     The character object statuses  401 ,  401 ′,  402 ,  402 ′,  403  and  403 ′ are stored in a register in the CPU  251  (a character object status register (character object status storing region)  456  schematically shown in FIG. 32) as character object statuses. When the game is started in the “easy” mode, the contents of the character object status register  456  are data representing the character object  401 . 
     A description has been made above on the three-dimensional line drawing image displayed on the screen of the display  18 A and the progress of the game in accordance with the manual controller  16 . 
     A description will now be made on the progress of the game in relation to the flow chart shown in FIG.  11 . 
     When the three-dimensional line drawing image  432  or the like shown in FIGS. 25 through 31 is shown, e.g., when the three-dimensional line drawing image  432  shown in FIG. 25 is displayed, it is checked at step S 28  whether any control button PB has been manipulated. 
     If no manipulation is determined, it is checked at step S 29  whether the character object line drawing image  401 Ib has reached a predetermined position of the obstacle object line drawing image  411 Ib, e.g., the leading position of the obstacle object line drawing image  411 Ib. If the character object line drawing image  401 Ib has not reached the predetermined position of the obstacle object line drawing image  411 Ib, NG flag F 1  is set at 0 at step S 30  because it is not an NG state, and processes at step S 23  and the subsequent steps are performed, i.e., the audio signal analyzing process at step S 26  and the line drawing display updating process at step S 27  are performed if there is any further music data. 
     During the line drawing display updating process at step S 27 , display with small vibrations is maintained because F 1 =0 at the determination of the NG flag F 1  at step S 75  (see FIG.  20 ). 
     When it is determined at step S 28  that a control button PB has been manipulated, it is determined at step S 31  whether the obstacle object has been cleared. Specifically, it is determined with reference to a predetermined pixel-number table (not shown) and the control buttons/obstacle objects correspondence table  416  shown in FIG. 16 whether a predetermined part of the character object line drawing image  401 Ib, e.g., the part of a front leg is located within a predetermined range from a predetermined position of the obstacle object line drawing image  411 Ib (e.g., the leading position of the obstacle object line drawing image  411 Ib) at the time of manipulation (the determination is actually made based on a certain number of pixels) and whether the appropriate control button PB, i.e., the L 1  button  114   a  to get over the obstacle object line drawing image  411 Ib has been manipulated or not. 
     When both of these conditions are satisfied, at step S 31 , it is determined that the obstacle object is cleared. At step S 32 , the NG flag F 1  is set in a state representing successful clearance, i.e., F 1 ←0. When the obstacle objects  411 ,  412 ,  413  and  414  are cleared, points are added to an unillustrated point register. 
     When either of those conditions is not satisfied, step S 31  determines that the obstacle object is not cleared. At step S 33 , the NG flag F 1  is set in a state representing unsuccessful clearance, i.e., F 1 ←1. 
     When it is determined at step S 29  that no control button PB has been manipulated, the NG flag F 1  is set in the F 1 ←1 (NG) state based on a judgement that the manipulation of the control buttons PB has been delayed even if the character object line drawing image  401 Ib or the like has reached a predetermined position of the obstacle object line drawing image  411 Ib or the like. 
     After the process (F 1 ←0) at step S 33 , it is determined at step S 34  whether the normalization of the character objects  401 ,  402  and  403  (i.e., a change in the direction of the arrow F in FIG. 32) is possible in the present state of display. For example, the term “normalization” means a change of the character object  401 ′ (see FIG. 32) into the character object  401  having smaller vibrations and a change of the character object  402  into the character object  401 ′ in the direction of the arrow F. 
     When the determination at step S 34  is YES, in other words, when it is determined with reference to the data in the character object status register  456  that the character object is in any of the statuses indicated by the  401 ′,  402 ,  402 ′,  403  and  403 ′ excluding  401 , at step S 36 , the data of the character object status register  456  is rewritten with data representing a character object in the direction of the arrow F. 
     Obviously, the determination at step S 34  is NO when the data of the character object status register  456  is data representing the character object  401 . 
     As assumed from the processes at steps S 32 , S 34  and S 36 , after the process (F 1 ←1) at step S 32 , it is determined at step S 35  whether the deterioration of the character objects  401 ,  402  and  403  (i.e., a change in the direction of the arrow B in FIG. 32) is possible in the present state of display. For example, the term “deterioration” means a transformation of the character object  401 ′ (see FIG. 32) into the character object  402  and a transformation of the character object  402  into the character object  402 ′ having bigger vibrations in the direction of the arrow B. 
     When the determination at step S 35  is YES, in other words, when it is determined with reference to the data in the character object status register  456  that the character object is in any of the statuses indicated by the  401 ,  401 ′,  402 ,  402 ′ and  403 , at step S 36 , the data of the character object status register  456  is rewritten with data representing a character object in the direction of the arrow B. 
     When the determination at step S 35  is NO, the data of the character object status register  456  is data representing the character object  403 ′. Then, the process proceeds to step S 11  (see FIG.  5 ). 
     The process proceeds to step S 11  as well when it is determined at step S 24  that the game has been finished for one piece of music. 
     FIGS. 33,  34  and  35  respectively show ending screens  457 ,  458  and  460  used in the process at step S 11  of the termination process at step S 12 . 
     Specifically, when the determination at step S 35  is negative, the ending screen  457  shown in FIG. 33 is displayed. 
     On the ending screen  457 , characters that read “game over! (meaning the end of the game)”, “once more? (asking whether the player wishes to play the game once more)”, “Yes” and “No” are displayed with small vibrations imparted thereto. When the ◯ button  112   b  is pressed in this state, the game can be played again. That is, step S 12  results in a negative determination and the game process at step S 10  is started. Then, the game selection screen  306  shown in FIG.  9  is displayed. 
     When “Exit” is selected on the game selection screen  306 , the start screen  300  shown in FIG. 6 appears. 
     The ending screen  458  shown in FIG. 34 is a screen that appears when “No” is selected on the ending screen  457  shown in FIG. 33 using the down button  110   c . When the ◯ button  112   b  is pressed in this state, step S 12  results in a positive determination. Then, the start screen  300  shown in FIG. 6 is displayed. 
     When step S 24  results in a positive determination, the ending screen (game clear screen)  460  shown in FIG. 35 is displayed. 
     On the ending screen  460 , characters that read “clear!” and “your score is 1570” are displayed with small vibrations imparted thereto. When the ◯ button  112   b  is pressed in this state, the game can be played again. That is, step S 12  results in a negative determination and the game process at step S 10  is started. Then, the game selection screen  306  shown in FIG. 9 is displayed. 
     FIG. 36 shows a functional block diagram for image processing and audio processing according to the above-described embodiment. 
     Referring to FIG. 36, audio signal analyzing means  502  has audio signal dividing means  504  for dividing an audio signal read from the optical disk  20  or a music CD or the like at predetermined time intervals, sampling means  506  for sampling the audio signal divided at the predetermined time intervals, frequency spectrum detecting means  508  for detecting frequency spectra from the result of the sampling, peak value detecting means  510  for detecting a peak value of each of the detected frequency spectra or detecting a peak value of a signal directly from the result of the sampling, order determining means  512  for determining a certain order by processing the detected peak values and non-linear object determining means (obstacle object determining means)  514  for determining the obstacle object  411  and the like based on the determined order. 
     The process of determining an order performed by the order determining means  512  will be described below. In a process on the frequency axis (frequency analysis process) which uses the frequency spectrum detecting means  508 , the detected peak values are categorized into peak values in frequency bands lower and higher than, for example, 500 Hz. Then, the detected frequencies are arranged in the order of the magnitude of the peak values in each of the high and low frequency bands. The arrangement of the detected frequency is used as the above order. In a process on the time axis (amplitude analysis process) which does not use the frequency spectrum detecting means  508 , peak values adjacent to each other on the time axis among the five greatest detected peak values are connected. Then, the gradient (differential value) between a peak value and the next peak value is defined as positive or negative. The arrangement of the positive and negative gradients is used as the above order. 
     The non-linear object determining means  514  refers to the table  428  or  429  showing correspondence between results of audio signal analysis and obstacle objects to be generated, determines a predetermined non-linear object (obstacle object) which is determined in advance in accordance with an order decided as described above and transmits the same to non-linear line drawing image generating means  516 . 
     In the functional block diagram for image processing and audio processing in FIG. 36, linear line drawing image generating means  518  and character object line drawing image generating means  520  are provided as line drawing image generating means in addition to the non-linear line drawing image generating means  516 . In this case, the character object line image drawing generating means  520  generates a predetermined character object line drawing image based on a determination made by character object line drawing image change determining means  524  which determines a change to be made on a character object line drawing image from a result of monitoring supplied by manipulation monitoring means  522  which monitors the manipulation timing of a predetermined control button PB on the manual controller  16 . 
     Movement imparting means  526  imparts a quantity of movement to the linear line drawing image, non-linear line drawing image and character object line drawing image. 
     Vibration quantity determining means  528  determines a quantity of vibration based on a result of monitoring performed by the manipulation monitoring means  522 . 
     Vibration imparting means  530  imparts different vibrations to each of the linear line drawing image, non-linear line drawing image and character object line drawing image to which a quantity of movement has been imparted based on the quantity of vibration determined by the vibration quantity determining means  528 . 
     The linear line drawing image, non-linear line drawing image and character object line drawing image to which movements and vibrations have been imparted are synthesized by synthesis means  532  and are drawn in the frame buffer  263  by drawing means  534 . 
     The image drawn in the frame buffer  263  is displayed on the screen of the display  18 A under control of display control means  536  (GPU  262 ). 
     As described above, the entertainment system  10  according to the present embodiment has the entertainment apparatus  12  for executing various programs, the manual controller  16  for inputting a manual control request of a user to the entertainment apparatus  12  and the display  18 A for displaying an image outputted from the entertainment apparatus  12 . The entertainment apparatus  12  has the audio signal analyzing means  502  for analyzing an audio signal and the line drawing image generating means  516 ,  518  and  520  for generating a substantially linear line drawing image having a non-linear line drawing image portion on the display monitor  18  by generating a substantially linear line drawing image ( 420 Ib or the like) and by inserting a non-linear line drawing portion ( 411 Ib or the like) based on a result of the analysis of the audio signal in the substantially linear line drawing image  420 Ib or the like and for generating a line drawing image of a character object ( 401 Ib or the like) on the substantially linear line drawing image having the non-linear line drawing image portion. 
     Specifically, a line drawing image of a character object ( 401 Ib or the like) is generated on a substantially linear line drawing image having a non-linear line drawing image portion which has been inserted based on a result of analysis of an audio signal ( 411 Ib and  420 Ib or the like). This makes it possible to display a novel line drawing image according to music on the display  18 A. 
     In this case, the movement imparting means  526  may move the line drawing image of the character object ( 401 Ib or the like) such that it makes a relative movement on the substantially linear line drawing image  420 Ib having the non-linear line drawing image portion  411 Ib, which makes it possible to provide a more entertaining line drawing image. 
     Further, the character object line drawing image change determining means (character object line drawing image changing means)  524  may change the character object line drawing image  401 Ib or the like to a line drawing image of a different character object ( 402 Ib or the like) depending on how the character object line drawing image moves on the substantially linear line drawing image  420 Ib or the like having the non-linear line drawing image portion  411 Ib or the like, which makes it possible to provide a more entertaining line drawing image. 
     Furthermore, the vibration imparting means  530  may impart vibrations to the substantially linear line drawing image  420 Ib or the like having the non-linear line drawing image portion  411 Ib or the like and the character object line drawing image  401 Ib or the like, which makes it possible to provide a quite entertaining line drawing image. 
     In this case, each of the line drawing images may be drawn as a three-dimensional line drawing image to provide a highly entertaining image which is less likely to become tiresome. 
     An audio signal may be used which is supplied to the entertainment apparatus  12  from a recording medium (the optical disk  20  or a music CD) or which is downloaded thereto as a result of communication. 
     Each of the above-described audio signal analyzing means  502 , the line drawing image generating means  516 ,  518  and  520 , the movement imparting means  526 , the character object line drawing image change determining means (character object line drawing image changing means)  524  and the vibration imparting means  530  may be stored in a recording medium such as the optical disk  20  as a program. 
     For example, the operation of the game of the present embodiment may be described with reference to FIG.  26 . The L 1  button  114   a  (the predetermined control button PB on the manual controller  16 ) is pressed at predetermined timing to cause the character object line drawing image  401 Ic to clear the virtual road object line drawing image  420 Ic having the obstacle object line drawing images  411 Ic,  414 Ic,  413 Ic and  412 Ic which move from the further right side of the screen toward the front left side of the screen (in the direction of the arrow E). 
     In this case, when the player misses the timing for pressing the control button PB or presses a control button PB of a wrong type, as shown in FIG. 30, the obstacle object line drawing image  411  to be cleared becomes the obstacle object line drawing image  411 Ig which is broken in such a manner that the original shape is indistinct, and the character object  401  changes to the character object line drawing image  401 Ig having considerably big vibrations. 
     The game operated in such a manner can be regarded quite entertaining. 
     The FIGS. 37 through 39 illustrate screens of match games (competition games) played by two game players according to other embodiments of the present invention. 
     In FIG. 37, a three-dimensional line drawing image  470  comprising a three-dimensional line drawing image  472  and a three-dimensional line drawing image  474  is displayed on a screen  468 . A character object line drawing image  401 I displayed at the lower left part of the screen  468  moves relative to an lower virtual road object line drawing image  420 I and a character object line drawing image  403 I displayed at the upper left part of the screen  468  moves relative to an upper virtual road object line drawing image  420 I, respectively. Specifically, obstacle object line drawing images  414 I,  411 I,  412 I,  413 I inserted in the respective virtual road object line drawing images  420 I move sequentially from the right side to the left side in the directions indicated by arrows E. 
     In this state, one game player controls the character object line drawing image  403 I in the upper three-dimensional line drawing image  472  by manipulating one of the manual controllers  16  and the other game player controls the character object line drawing image  401 I in the lower three-dimensional line drawing image  474  by manipulating the other of the manual controllers  16  to play a match game (competition game). 
     In this game, the upper three-dimensional line drawing image  472  is displayed in reddish color and the lower three-dimensional line drawing image  474  is displayed in bluish color so that the game players can recognize their own game courses at a glance. 
     Since the same music data is used for generating each of the upper game course and the lower game course, types and orders of the generated obstacle object line drawing images in the game courses are the same as shown in the screen  468  of FIG.  37 . 
     An arc-shaped line drawing image  476 I displayed at the lower part of the screen  468  indicates a length (duration) for one piece of music. The arc-shaped line drawing image  476 I comprises a thick solid line drawing image and a thin solid line drawing image. The thick solid line drawing image indicates a part of a music piece which has already been reproduced and the remaining thin solid line drawing image indicates a part of the music piece which has not yet been reproduced. That is, the game players can recognize the progress of the music piece from the border between the thick solid line drawing image and the thin solid line drawing image. When the arc-shaped line drawing image  476 I becomes the thick solid line drawing image in its entirety, the game corresponding to the music piece is completed. In this game, the color of the thick solid line drawing image the color of the thin solid line drawing image are different. 
     In this embodiment, unlike conventional match games (competition games), the screen is not divided for displaying game images for two game players. Rather, the three-dimensional drawing images  472  and  474  for game courses of game players are displayed in a different color in the same screen  468 , respectively. Accordingly, a new fresh music game can be played by two game players at the same time. 
     In FIG. 37, the three-dimensional line drawing images  472  and  474  are displayed in substantially parallel in a different color. In FIG. 38, the three-dimensional line drawing images  482  and  484  are displayed diagonally to cross each other in a different color. 
     As described above, the game can be played by two game players at the same time using the same music piece. However, the game is not limited to a type in which the game players compete simply for obtaining a score or the like. According to another embodiment of the present invention, if one game player clears a predetermined number of obstacle object line drawing images successively, a barrier is generated momentarily on the next obstacle object line drawing image to be cleared (or a part of the virtual road object  420  is removed momentarily on the next obstacle object line drawing image to be cleared) in the other game player&#39;s game course. In this case, it is no longer possible for the other game player to clear the next obstacle object line drawing image even if the other game player is succeeded in pressing a predetermined control button at a proper predetermined timing. 
     For example, as shown in FIG. 39, when one game player clears many obstacle object line drawing images successively, line drawing images are displayed radially like a firework around the character object line drawing image  401 I of one of the three-dimensional line drawing image  490  in the three-dimensional line drawing image  488 . At the same time, a barrier is displayed (or a part of the virtual road object  420  is removed) on the next obstacle object line drawing image  414 I of the other of the three-dimensional line drawing image  492  in the three-dimensional line drawing image  488 . Line drawing images are also displayed radially around the obstacle object line drawing image  414 I. If this occurs, the other game player can not clear the obstacle object line drawing image  414 I any more. 
     In this manner, the manipulation of one game player may affect the game course of the other game player. Accordingly, a further amusing aspect can be added to the match game to excite the feelings of the game players. 
     The present invention is not limited to the above-described embodiments, and various configurations may obviously be employed without departing from the principle of the invention. 
     (1) For example, as an alternative example of the control buttons/obstacle objects correspondence table  416 , i.e., so-called key assignment shown in FIG. 16, an control buttons/obstacle objects correspondence table  416 A shown in FIG. 40 may be stored in addition. On the control buttons/obstacle objects correspondence table  416 A, either the L 1  button  114   a  or L 2  button  114   b , either the R 1  button  116   a  or R 2  button  116   b , the down button  110   d  and the X button  112   c  are assigned to the obstacle objects  411 ,  412 ,  413  and  414 , respectively. Such an arrangement makes it possible to satisfy preference of a user (game player) and the like. 
     (2) For example, an obstacle object  602  obtained by synthesizing the obstacle objects  414  and  412  with the synthesis means as shown in FIG. 41 may be generated in the tables  428  and  429  of correspondence between results of audio signal analysis and obstacle objects to be generated shown in FIGS. 18 and 19, as the obstacle object generated based on the audio signal analyzing process at step S 26 . The user may need to press the R 1  button  116   a  and X button  112   c  simultaneously at predetermined timing (in a predetermined range) to allow the character object  401  or the like to clear the obstacle object  602 . 
     Various synthesized obstacle objects  604 ,  606 ,  608 ,  610  and  612  as shown in FIG. 42 may be generated (created) as synthesized obstacle objects in addition to the synthesized obstacle object  602 . 
     (3) In order to simplify the operation of the game, the name registration process may be omitted by displaying the game selection screen  306  shown in FIG. 9 without performing the name registration process (step S 7 ) described with reference to FIGS. 7 and 8 when the start button  40  is pressed with the start screen  300  being displayed. 
     (4) Furthermore, a special movement may be added to the obstacle objects  411 ,  412 ,  413  and  414  and the virtual road object  420 . First, for example, the moving speed of the virtual road object line drawing image  420 Ib can be abruptly changed by setting the game program accordingly in relation to the element of music (a piece of music) or regardless of the element of music. Second, for example, the speed of the obstacle object drawing image  412 Ib in FIG.  25  may increase such that the obstacle object drawing image  412 Ib passes the obstacle object line drawing image  413 Ib located in front of the same. Third, as seen on a three-dimensional line drawing image  622  displayed on a screen  620  of the display  18 A in FIG. 43, obstacle object line drawing images  602 Iia and  602 Iib may be displayed such that they rotate to the right and (or) left about a virtual road object line drawing image  420 Ii while moving in the direction of the arrow E. It is to be understood that these modifications for displaying images can be applicable to the above described match game for two game players. 
     As described above, the present invention makes it possible to display a novel line drawing image on a display screen or the like. 
     Further, according to the invention, a line drawing image of a character object is generated on a substantially linear line drawing image having a non-linear line drawing image portion based on a result of audio signal analysis. This makes it possible to display a novel line drawing image on a display screen or the like according to music. 
     The invention further makes it possible to display a line drawing image having vibrations on a display screen. 
     Games in which line drawing images are displayed on a screen can be widely accepted by people in different generations including children and old people because they give a heartwarming feeling. 
     Each of the line drawing images may be drawn as a three-dimensional line drawing image to provide a highly entertaining image which is less likely to become tiresome associated with music. 
     Next, an audio signal analyzing process according to another embodiment of the present invention will be described in the following explanations (A. BRIEF EXPLANATION, B. DETAILED EXPLANATION). 
     A. Brief Explanation 
     The audio signal analyzing process comprises the following four steps (steps A1 through A4). 
     A1: Reading an audio signal in the optical disk (music CD)  20  and storing the read audio signal in the buffer (long buffer)  283  or the main memory  253   
     A2: Emphasizing attacks in the music (audio sound) expressed by the audio signal stored in the long buffer  283   
     A3: Selecting audio events 
     A4: Shadowing unnecessary audio events from the selected audio events and determining the resulting audio events as the final events (event shadowing) 
     Firstly, the process in step A1 will be described. Specifically, an audio signal is read from a music CD or the like via the optical disk drive  281  and the decoder  282 . The read audio signal is stored in the long buffer  283 . The audio signal in the long buffer  283  is delayed for a predetermined period of time. 
     The delay time allows audio events in the read audio signal to be detected and displayed as road parts such as the obstacle object line drawing image  411 I on the display  18 A in synchronism with the output of the corresponding audio sound from the speaker  18 B via a D/A converter (not shown) in the SPU  271 . 
     That is, the delay time is sufficient for the CPU  251  to detect distinctive attacks (hereinafter also referred to as the distinctive points or the potential events) in the audio signal for determining road parts corresponding to the detected attacks in the audio signal. 
     The audio signal comprises a sinusoidal wave signal having a variably changing value (the audio signal has different values on the time axis). Each of positive values and negative values extracted as a sampling value constitutes an audio event. That is, positive audio events and negative audio events are alternately repeated in the audio signal. In particular, distinctive events (attacks) in the audio events in the audio signal are referred to as the distinctive points or the potential events. 
     Next, the process in step A2 will be described. The audio signal is preprocessed to emphasize the attacks in the music (audio sound). The emphasized audio signal can be expressed by the ratio (Ps/Pl) of a short term power Ps to a long term power Pl in the audio signal. The short term power Pl is calculated based on a short term Ns before an analysis point and the long term power Pl is calculated based on a long term Nl before the analysis point. 
     More specifically, a certain point in the audio signal is determined as the analysis point. Then, a short period of time, for example, about 23 ms before the analysis point is determined as the short term Ns. Similarly, a long period of time, for example, about 186 ms before the analysis point is determined as the long term Nl. 
     Generally, a plurality of audio events are included in each of the short term Ns and long term Ls. The short term Ns and long term Nl are also referred to as the short term block and a long term block, respectively. 
     The short term power Ps and the long term power Pl can be calculated in the following manner. The short term power Ps is taken to be the sum of the squares of the short term block&#39;s sampling values. The long term power Pl is taken to be the sum of the squares of the long term block&#39;s sampling values. 
     The squares are used for emphasizing sampling values. For example, a sampling value greater than 1 is made much greater by multiplying itself. A sampling value smaller than 1 is made much smaller by multiplying itself. Further, the squares are used for converting negative sampling values into positive sampling values which are suitable as power values. 
     That is, the emphasized signal is the ratio of the present (short term power Ps) to the recent past (long term power Pl). The long term power Pl is smallest at the start of an audio event, and rises as the event enters the long term block. As a result, the start of an audio event is boosted by the long term power Pl in the denominator, and this boost tapers off as the event persists, Therefore, this algorithm tends to emphasize attacks in the music. 
     Next, the process in step A3 will be described. Event selection is controlled by a “select period”. At most one event will be generated per select period. The length of the select period determines the maximum event rate. 
     In order to be considered for event selection, the emphasized signal must be greater than a threshold value. After thresholding, the peak emphasized signal (short term power Ps/long them power Pl) during each select period is chosen as a potential event. The ratio of the short term power Ps to the long term power Pl of the potential event is its “peak ratio”. 
     Next, the process in step A4 will be described. To prevent overlapping road parts on the screen of the display  18 A, the game&#39;s geometry dictates a minimum spacing between potential events. Event shadowing drops potential events that would violate this constraint. The remaining events are defined as final events. 
     An event&#39;s time extent is its “road part period”. The minimum time between two events is taken to be two times the first event&#39;s road part period—this is called the event&#39;s “shadow period”. No event may occur in another event&#39;s shadow period. 
     When a potential event is selected, the potential event is temporarily stored in a memory. If its shadow period does not pass before another potential event is selected, the peak ratios of two events are compared and the event with the smaller ratio is dropped. Thus, the potential event with the larger ratio is determined to be the final event. 
     In this manner, a final event signal (final event array) having a series of final events is generated. When each of the final events is reproduced, one road part is displayed. The shape of the road part displayed in each of the final events is determined based a predetermined sequence distribution or weight random distribution. 
     In summary, according the audio analyzing process, the delay buffer gives time for analysis and graphic display in step A1, the emphasis algorithm highlights interesting events in the audio signal in step A2, event selection produces events with a desired maximum event rate in step A3, and, event shadowing drops events that violate spacing constraints in step A4. 
     The audio analyzing process comprising the combination of these steps can be effectively performed to generate interesting events from an audio signal. 
     B. Detailed Explanation 
     Next, each process performed in steps A1 through A4 will be described specifically in the following sections (B1 Object, B2 Brief explanation of waveform processing, B3 Detailed explanation of waveform processing (B3a Emphasize process, B3b Event selection process, B3c Shadowing process)) with reference to drawings illustrating waveforms. 
     B1. Object 
     FIG. 44 shows a digital audio input signal  700  of an original sound used in a game. The audio signal  700  is read from a music CD or the like and stored in the long buffer  283 . The audio signal  700  is shown in an analog waveform for the purpose of brevity. In this example, amplitude values are shown in the range form the minimum value −0.5 to the maximum value of +0.5 as defined by the vertical axis. The horizontal axis is a time axis for 1.6 seconds. As described above, the audio signal  700  includes positive audio events and negative audio events which are repeated alternately. 
     In this game, it is necessary to extract distinctive points in music and display road parts (obstacle objects) corresponding to the extracted distinctive points on the display  18 A synchronously with the music. 
     Therefore, a system for analyzing a waveform of music for identifying distinctive points in the music is needed. 
     As shown in FIG. 45, the audio signal  700  has distinctive points indicated by arrows  702 . In reproducing the audio signal  700 , these distinctive points can be emphasized as attacks in the music. Therefore, it is preferable to extract audio events at the respective distinctive points indicated by the arrows  702  by a suitable process. 
     That is, the audio analyzing process according to the present embodiment is intended to analyze music (the waveform of the audio signal  700  shown in FIG. 44) so as to identify attacks in the music (the distinctive points indicated by the arrows  702  in FIG.  45 ). In the game, positions for displaying road parts on the display  18 A are determined based the identified distinctive points. 
     When the audio analyzing process is applied to the game according to the present invention, it is necessary to select suitable points from the distinctive points indicated by the arrows  702  in FIG.  45  and eliminate the remaining unsuitable points depending on game level settings or the like. 
     That is, the purpose of the audio analyzing process according to the present embodiment is to extract certain final events based on attacks (distinctive points) in the audio signal (music) recorded in a music CD or the like for utilizing the final events in the game according to the present invention. 
     B2. Brief Explanation of Waveform Processing 
     As described above, FIG. 44 shows a waveform of an audio signal  700  which is read from a music CD or the like and stored in the long buffer  283 . 
     FIG. 46 shows a waveform of an emphasized signal  704 . The emphasized signal  704  is obtained by emphasizing rising parts of the waveform, i.e., by emphasizing attacks in the music. The emphasizing process will be described later in detail. In FIG. 46, amplitude values are shown in the positive range from 0 to the maximum value of 1.0 as normalized by the vertical axis. The horizontal axis is a time axis indicating respective sampling points. 
     FIG. 47 shows a waveform of a signal indicating attack events  706 . The signal is obtained by converting the emphasized signal  704  with a threshold TH (see FIG. 46) to eliminate unnecessary parts of the waveform. 
     FIG. 48 shows a waveform of a signal indicating potential events  708 . The signal is obtained by dividing the time axis into a plurality of blocks (select periods) and extracting a peak in each of the divided blocks. 
     It is to be understood that the potential events  708  correspond to the distinctive points indicated by the arrows  702  in FIG.  45 . 
     FIG. 49 shows a signal indicating final events  710 . The final events  710  are selected from the potential events  708  based on the game system. 
     FIG. 50 shows positions of the final events in the music (audio signal of FIG.  44 ). The final events are extracted from the positions indicated by arrows  712 . 
     B3. Detailed Explanation of Waveform Processing 
     B3a. Emphasize Process 
     The emphasize process is intended to obtain the emphasized signal  704  of FIG. 46 from the audio signal  700  of FIG.  44 . 
     FIG. 51 shows an enlarged view showing a part of the audio signal  700  in FIG.  44 . The audio signal  700  is partially extracted and expanded on the time axis. 
     The emphasis process can be performed each time a sampling value is obtained. However, for the purpose of brevity, the emphasis process at a point of time n 1  and the emphasis process at a point of time n 2  will be described only. 
     A short period of time, for example, 23 ms before the time point n 1  (or n 2 ) is defined as a short term block Ns of n 1  (or n 2 ). 
     Further, a long period of time, for example, 186 ms before the time point n 1  (or n 2 ) is defined as a long term block Nl of n 1  (or n 2 ). 
     In FIG. 51, it is appreciated that the fluctuation of the waveform is large near the time point n 1  in comparison with the fluctuation near the time point n 2 . That is, the time point n 1  (the waveform near the time point n 1 ) is considered to be more distinctive than the time point n 2  (the waveform near the time point n 2 ). 
     The total sum of values of the audio events (sampling values of the waveform) near the time point n 1 , i.e., short term power Ps (n 1 ) is larger than the total sum of values of the audio events near the time point n 2 , i.e., short term power Ps (n 2 ). Therefore, the waveform near the time point n 1  is considered to be distinctive in comparison with the waveform near the time point n 2 . 
     Next, the method of emphasizing the waveform around the time points n 1  and n 2  will be described. In emphasizing the waveform around the time points n 1  and n 2 , the long term blocks Nl are taken into consideration. 
     The degree of the fluctuation of the present waveform can be effectively considered by comparing the present waveform with the past waveform. That is, if the fluctuation of the past waveform is small, the fluctuation of the present waveform is considered to be comparatively large, i.e., the present waveform is considered to be distinctive. 
     More specifically, in FIG. 51, the total sum of values of the audio events in the long term block Nl near the time point n 1 , i.e., long term power Pl (n 1 ) is smaller than the total sum of values of the audio events in the long term block Nl near the time point n 2 , i.e., long term power Pl (n 2 ). Therefore, the waveform near the time point n 1  is considered to be distinctive. 
     As described above, when the ratio of the short term power Ps to the long term power Pl is large at a time point, the waveform near the time point is considered to be distinctive. In FIG. 51, it is possible to analyze the degree of the fluctuation at the time point n 1  from the ratio Ps (n 1 )/Pl (n 1 ), and analyze the degree of the fluctuation at the time point n 2  from the ratio Ps (n 2 )/Pl (n 2 ). That is, it is possible to emphasize the audio events in the waveform near the time points n 1  and n 2  from the ratios. The signal emphasized by the above process is defined as the emphasized signal. 
     In the example of FIG. 51, since Ps (n 1 )/Pl (n 1 ) is much larger than Ps (n 2 )/Pl (n 2 ), the waveform near the time point n 1  is considered to be much more distinctive than the waveform near the time point n 2 . 
     Next, a quantitative method of calculating the total sum of the values of audio events, Ps (n), Pl (n) will be described. 
     In FIG. 52, powers of audio events at respective time points na and nb are defined. 
     When a value of the audio event at the time point na is M (na), the power of the audio event at the time point na corresponds to the area shown by a shaded portion defined by the following expression: 
     
       
           M ( na )× M ( na )=SQUARE( M ( na ))&gt;0 
       
     
     Similarly, when a value of the audio event at the time point nb is M (nb), the power of the audio event at the time point nb corresponds to the area shown by a shaded portion defined by the following expression: 
     
       
           M ( nb )× M ( nb )=SQUARE( M ( nb ))&gt;0 
       
     
     A total sum of powers of audio events in a short term block at a time point n is defined as the short term power Ps (n). 
     A method of calculating a short term power Ps (n) in a short term block at a time point n is described below. 
     For example, at the time point n 1  shown in FIG. 51, the short term power Ps (n 1 ) is expressed by the total sum of powers obtained at respective sampling points q in the short term block Ns (n 1 ). The short term block Ns (n 1 ) indicates a period of time from the time point n 1 −Ns to the time point n 1 . That is, the short term power Ps is the sum of the squares of the short term block&#39;s sampling values (SUM SQUARE (M (q))). 
     A total sum of powers of audio events in a long term block at a time point n is defined as the long term power Pl (n). 
     A method of calculating a long term power Pl (n) in a long term block at a time point n is described below. 
     For example, at the time point n 1  shown in FIG. 51, the long term power Ps (n 1 ) is expressed by the total sum of powers obtained at respective sampling points q in the long term block Nl (n 1 ). The long term block Nl (n 1 ) indicates a period of time from the time point n 1 −Nl to the time point n 1 . That is, the long term power Ps is the sum of the squares of the long term block&#39;s sampling values (SUM SQUARE (M (q))). 
     In this manner, a short term power Ps (n) and a long term power Pl (n) at a time point (n) can be calculated. 
     FIG. 53 is a graph showing short term powers Ps of the audio signal  700  in FIG.  44 . In the vertical axis, 1e+10 signifies 1×e 10  (e is a base of natural logarithm). 
     FIG. 54 is a graph showing long term powers Pl of the audio signal  700  in FIG. 44 in addition to the short term powers Ps in FIG. 53 (scaling of the vertical axis is changed). 
     FIG. 55 is a graph showing an emphasized signal  704 . The emphasized signal  704  comprises the ratio (Ps/Pl) of the short term power Ps to the long term power Pl. FIG.  55  and FIG. 46 are the same graph. 
     B3b. Event Selection Process 
     The event selection process is intended to partially eliminate the emphasized signal  704  using a threshold TH. That is, parts (ratios Ps/Pl) of the emphasized signal which do not exceed the threshold value TH are eliminated. Further, the time axis is divided into a plurality of select periods. The length of the select period is related to the scrolling speed in the game. Therefore, the length of the select period is determined based on game level settings. 
     FIG. 56 shows an emphasized signal indicating attack events  706 . The signal is obtained by partially eliminating the emphasized signal  704  using the threshold TH. The time axis is divided into twelve select periods # 1  thorough # 12 . 
     Then, peak ratios are detected in the respective select periods # 1  through # 12 . The peak ratios are defined as the potential events PE. The array of the potential events PE is defined as the potential signal  708 . 
     The positions of the potential events PE constituting the potential signal  708  are substantially corresponding to the positions of the audio events of the audio signal  700  indicated by the arrows  702  in FIG.  45 . 
     B3c. Event Shadowing 
     The event shadowing process is intended to eliminate unnecessary potential events PE in the game system and to control the game level. 
     In the event shadowing process, a shadow period SP is determined as a parameter in setting a game level. 
     Final events FE needed in the game are selected from potential events PE indicating distinctive points of the music. 
     Specifically, the event shadowing process comprises the following three steps (steps  1  through  3 ). 
     In step  1 , a potential event PE in the present shadow period is selected. Then, it is determined whether another potential event PE is included in the present shadow period. That is, in step  1 , it is determined whether a plurality of potential event PE are included in the same shadow period of the selected potential event PE or not. 
     If it is determined that another potential event PE is not included in the shadow period of the selected potential event PE in step  1 , control passes to step  2 . 
     In step  2 , the selected potential event PE is determined as an effective final event. Then, control passes back to step  1  for selecting the next potential event PE on the time axis. 
     If it is determined that another potential event PE is included in the shadow period of the selected potential event PE in step  1 , control passes to step  3 . 
     In step  3 , a potential event PE having the largest peak value is selected in the present shadow period as a final event FE. If two or more potential events PE having the same peak ratio are included in the present shadow period, the earliest potential event PE on the time axis is selected as a final event. The remaining potential events PE are eliminated. Then, the control passes back to step  1 . 
     The above steps  1  through  3  will be described specifically with reference to FIG. 58 (FIG.  58  and FIG. 57 are the same graph). Firstly, a potential event PE in the first shadow period # 1  is selected. The first shadow period # 1  includes three select periods # 1  through # 3 . That is, there are two potential events PE (a potential event PE in the first select period # 1  and a potential event PE in the second select period # 2 ) in the first shadow period # 1 . 
     In this case, as described above, the potential event PE in the first select period # 1  is selected and the potential event PE in the second select period # 2  is eliminated in step  3 . That is, the potential event PE in the first select period # 1  is extracted as the effective final event FE in the first shadow period. Next, the potential event PE in the select period # 4  is selected as the next final event FE, since the potential event PE in the second select period # 2  has already been eliminated as described above. In the shadow period # 4 , there are three potential events PE (the potential event PE in the select period # 4 , the potential event PE in the select period # 5 , and the potential event PE in the select period # 6 ). Then, the potential event PE in the select period # 6  is selected as the final event and the other potential events PE in the select periods # 4  and # 5  are eliminated. 
     Then, control passes back to step  1 . There are three potential events PE in the next shadow period # 6  (the potential event PE in the select period # 6 , the potential event PE in the select period # 7 , and the potential event PE in the select period # 8 ). In step  3 , the potential event PE in select period # 6  is selected again as the final event FE and other potential events PE in the select periods # 7  and # 8  are eliminated. Then, control passes back to step  1 . 
     By repeating the above process, as shown in FIG. 59, three effective final events FE can be extracted from eleven potential events PE of FIG.  58 . 
     At the positions of the final events FE, obstacle objects  411  or the like are generated as road parts. 
     The type of obstacle object  411  or the like is determined by the process which was described with reference to FIG.  19 . 
     As described above, the entertainment system as applied to the embodiment according to the present invention comprises the buffer  283 , audio signal analyzing means (the CPU  251 ), and road part generating means (the CPU  251 ). The buffer  283  stores an audio signal  700  for a certain period of time. The audio signal  700  includes sampling values constituting continuous events, i.e., positive audio events and negative audio events. The audio signal analyzing means reads the audio signal  700  from the buffer  283  and analyzes the audio events in the read audio signal  700  as distinctive points so as to select final events FE. The road part generating means generates objects such as road parts  411  or the like to be displayed on the screen of the display  18 A. 
     According to the present embodiment, the CPU  251  as the audio signal analyzing means has a first function to generate an emphasized signal  704  by calculating a ratio of Ps/Pl, i.e., a ratio of a short term power (Ps) in a predetermined short period before a time point (sampling point) to a long term power (Pl) in a predetermined long period of time before the time point (sampling point) at each of the time points (sampling points) so as to emphasize sampling values obtained in the sampling points. 
     Further, the audio analyzing means has a second function to partially extract the emphasized signal by comparing the values in the emphasized signal  704  and a threshold TH. Specifically, parts of the emphasized signal  704  having values smaller than the threshold TH is eliminated and the remaining parts of the emphasized signal  704  having values equal to or larger than the threshold TH are extracted. 
     Further, the audio analyzing means has a third function to determine potential events PE by dividing the emphasized signal  704  into a plurality of select periods having a predetermined period of time and selecting peak values in the respective select periods. 
     Further, the audio analyzing means has a fourth function to select final events FE from the potential events PE. Specifically, shadow periods each having at least two times longer than the select period are assigned in the overall period of the audio signal such that each shadow period starts one of the potential events PE. Then, the largest potential event PE is selected as the final event FE. 
     Preferably, a short term power is the sum of the squares of sampling values in a short term block and the long term power is the sum of the squares of sampling values in a long term block. 
     The road part generating means may generate road parts to be displayed on the display  18 A based on combinations of positive and/or negative gradients between respective adjoining peaks of the selected final events FE.