Patent Publication Number: US-6700047-B2

Title: Enhanced mechanical acoustic sound generation system and method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to enhancing the sound quality of mechanical acoustic sound generation devices, and more particularly enhancing the sound quality of mechanical acoustic musical instruments. 
     2. Description of Related Art 
     Mechanical acoustic sound generation devices, in particular, mechanical acoustic musical instruments are created to produce high quality sound. These instruments&#39; sound quality vary, typically as a function of their size and quality of their materials, construction, and mechanisms. For example, concert grand pianos that are large, very carefully engineered, and made with the highest quality materials and mechanisms produce very high quality perceived sound. Similarly, concert cellos that are large and constructed of the finest materials produce high quality perceived sound. 
     Due to costs, limited raw materials, and high volumes, all acoustic sound generation devices manufactured do not produce high quality perceived sound. Some more affordable devices, available to the average consumer, have a perceived sound quality far below their expensive counterparts. An object of the present invention is to enhance the sound quality of more affordable mechanical acoustic sound generation devices while not employing the expensive materials, mechanisms, or assembly methods of superior mechanical acoustic sound generation devices. 
     SUMMARY OF THE INVENTION 
     The present invention includes a system and method for enhancing the perceived sound quality of a first mechanical acoustic sound generation device. The first device is capable of producing a first plurality of notes each note having a fundamental frequency. In this first device, a second, smaller plurality of the first plurality of the notes have a perceived sound quality lower than the perceived sound quality of corresponding notes produced by a second mechanical acoustic sound generation device. The invention enhances the perceived sound quality of the first device by determining when a note is generated by the first mechanical device and determining whether the note is one of the second, smaller plurality of the first plurality of notes. When the determined note is one of the second, smaller plurality of the first plurality of notes, the invention generates an acoustic representation of a corresponding note digitally sampled from the second mechanical device. Thereby, enhancing notes produced by the first device with digital sampled representations of notes produced by the second device. 
     In one embodiment the first mechanical acoustic sound generation device is a mechanical acoustic musical instrument and the second mechanical acoustic sound generation device is a mechanical acoustic musical instrument. In another embodiment, the first mechanical acoustic sound generation device is a mechanical acoustic piano and the second mechanical acoustic sound generation device is a mechanical acoustic piano. For this embodiment the second, smaller plurality of the first plurality of notes have a fundamental frequency range from about 0 Hertz to 261 Hertz. Further, the invention generates an acoustic representation of a corresponding note digitally sampled from the second mechanical device where the amplification of the acoustic representation of the corresponding note varies. In one embodiment, the amplification of the acoustic representation of the corresponding note varies linearly on a decibel scale with the greatest amplification at the lowest fundamental frequency range. In another embodiment, a user may select the overall amplification level of the acoustic representations of the corresponding notes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded illustration of a prior art mechanical acoustic sound generation device (concert piano). 
     FIG. 2 is a block diagram of an enhanced mechanical acoustic sound generation device in accordance with the present invention. 
     FIG. 3 is a block diagram of an exemplary electronic sound generation controller of the enhanced mechanical acoustic sound generation device shown in FIG. 2 in accordance with the present invention. 
     FIG. 4A is a graph of one exemplary high gain response for an enhancement signal in accordance with the present invention. 
     FIG. 4B is a graph of one exemplary medium gain response for an enhancement signal in accordance with the present invention. 
     FIG. 4C is a graph of one exemplary low gain response for an enhancement signal in accordance with the present invention. 
     FIG. 4D is a graph of an exemplary variable gain response for an enhancement signal in accordance with the present invention. 
     FIG. 5 is a flowchart of a process of creating sound signals to be used in an electronic sound generation enhancement process in accordance with the present invention. 
     FIG. 6 is a flowchart of the electronic sound generation enhancement process in accordance with the present invention. 
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Throughout this description, the preferred embodiment and examples shown should be considered as exemplars, rather than as limitations on the present invention. 
     One embodiment of the present invention is presented in reference to FIG.  1 . FIG. 1 (Prior Art) is an exploded view of one mechanical acoustic sound generation device  10 , in particular a concert grand piano. The mechanical acoustic device  10  is a mechanical acoustic musical instrument (piano) that generates acoustic sound. The device  10  includes a keyboard  12 , case  14 , soundboard  16 , and frame  18 . The case  14  has legs  26  and damping pedals  24 . The frame  18  includes a plurality of tightly strung strings  32  divided into a bass section  32  and treble section  34 . The soundboard  16  is coupled to the frame  18  via the bridge  28 . The keyboard  12  includes an action  22  where the action  22  strikes string(s)  32  of the frame  18  when one or more keys of the keyboard  12  are struck and each key represents a musical note. The struck string(s) vibrate and the soundboard  16  receives the vibrations via the bridge  28  and amplifies the vibrations, producing the majority of acoustic sound/musical notes generated by the device  10 . The bridge  28 , frame  18 , other strings (due to harmonics)  32 , and case  14  also provide some of the acoustic sound generated by the device  10  when one or more keys of the keyboard  12  are struck or depressed (creating a “ching” effect). 
     Unless struck strings are damped, subsequent depressed keys may generate acoustic sound/musical notes that are “colored” by concurrently vibrating strings representing previous or simultaneously depressed keys (creating a “ring” effect). Also, the sound frequency spectrum generated when a string is struck varies as a function of the string length. In device  10 , the piano&#39;s bass section  34  string  32  lengths and some of the treble sections  36  string  32  lengths may affect the perceived sound quality of corresponding notes generated when these strings  32  are vibrated. Smaller, usually less expensive pianos have shorter bass section  34  strings and some shorter treble section  36  strings  32  compared to large, usually more expensive concert grand pianos. For example, the bass section  34  string  32  that generates the lowest musical scale D note when vibrated is about seven feet long in larger concert grand pianos (devices  10 ) while generally four feet long or less in smaller, less expensive devices  10 . In addition, smaller pianos tend to have smaller soundboards made of less expensive materials where the device&#39;s  10  soundboard  16  size area and material composition may also affect the device&#39;s perceived acoustic sound quality. Other mechanical acoustic sound generation devices&#39;, such as cellos, violins, guitars, sound quality may also vary as a function of size, materials, and ultimately cost. 
     FIG. 2 is a block diagram of an enhanced mechanical acoustic sound generation device  100  in accordance with the present invention. The enhanced device  100  includes a mechanical acoustic sound generation device  10  and electronic sound generation enhancement system  40 . In an exemplary embodiment, the mechanical acoustic sound generation device  10  is modified to enhance its perceived sound quality where the device  10  is perceived to produce lower sound quality compared to a similar or related mechanical acoustic sound generation device, e.g., a smaller piano (baby grand, upright) modified so its perceived sound quality compares favorably to a larger, better constructed (materials and build quality), usually more expensive piano (concert grand). In particular, the electronic sound generation enhancement system  40  supplements the mechanical sound generated by the device  10  so its perceived sound quality compares more favorably with a similar device having a perceived high sound quality. 
     The inventor has noted that difference in perceived sound quality between high and low end devices generally varies along the frequency spectrum of the sounds generated by the devices with some spectrum sections having minimal differences and others having more significant differences (in perceived sound quality). For example high and low end pianos generally have the greatest difference in perceived sound quality at the lower end of their frequency spectrum of of the sounds they generate. Further, the perceived sound quality difference decreases as the generated sound&#39;s fundamental frequency increases to where at mid or higher level frequencies (of generated sound) the difference is not detectable or insignificant. The present invention determines this characteristic and provides variable enhancement based on the differences in perceived sound quality between corresponding high and low end mechanical acoustic sound generation devices in which the invention is employed. 
     In an exemplary embodiment, the invention samples the sounds generated by the corresponding higher perceived sound quality device for the notes that have a detectable or significant difference in sound quality. The exemplary embodiment then regenerates these sampled sounds using a synthesizer to enhance the lower end device when the device generates a sound in a region having a detectable or significant difference in perceived sound quality. In one embodiment a user of the enhanced device may selectably change the amplitude level or gain of these added sound signals. One exemplary enhancement system  40  for use with a piano is shown in FIG.  2  and explained with reference to FIGS. 3 to  6 . 
     The exemplary piano enhancement system  40  includes a controller  44 , an electric acoustic sound generation device  46 , and sound/note detection system  42 . The sound/note detection system  42  determines when one or more notes/sounds are in the process of being generated by the device  10  and transmits this information to the controller  44  via line  43 . When desirable (the perceived quality difference significant for one or more of the notes/sound being generated) the controller  44  generates an enhancement signal. The signal is transmitted to the electric acoustic sound generation device  46  via line  45  and converted to acoustic sound by the device  46  where the electrically generated acoustic sound merges with the device&#39;s lo mechanically generated acoustic sound, improving the perceived quality of the overall produced sound. 
     FIG. 3 is a block diagram of an exemplary controller  44  in accordance with the present invention. The controller  44  includes a main processor  52 , non-violate memory  54 , user control panel  56 , and synthesizer/Digital Signal Process (“DSP”)  58 . The processor  52  may be a microprocessor or other device that can receive signals from the note detection system  42  and selections from the user control panel  56 . Exemplary use of the enhancement system  40  is presented with reference to FIGS. 4A to  6  where the device  10  is a mechanical acoustic musical instrument, in particular a piano  10 . FIG. 5 is an algorithm of an exemplary process  70  of sampling the sounds generated by the corresponding higher perceived sound quality device that have a detectable or significant difference in sound quality than the device to be enhanced. 
     In step  71 , the process  70  determines which notes/sounds need to sampled from an ideal source (high quality mechanical acoustic sound generation device). For pianos, the inventor has noted that less expensive, smaller pianos produce low to mid frequency sounds having a perceived sound quality lower than a high quality, larger piano (ideal source) with the greatest difference at the lowest frequencies and least difference at the mid to upper frequencies of sound spectrum produced by the piano  10 . In one embodiment, the algorithm  70  determines that the device&#39;s  10  notes that need to enhanced range from its lowest note (musical scale bottom “A”) to the note corresponding to the musical scale middle “C”(step  71 ). Then the algorithm  70  causes the idea source to generate the notes to be sampled (step  72 ), samples the notes as generated (step  74 ), and stores the samples for each note (step  76 ). 
     In the case of the piano  10  to be enhanced, the ideal source is caused to generate a range of notes from its lowest note to the note corresponding to the musical scale middle “C”. In one embodiment, the ideal source is a Steinway D concert grand piano. The musical scale note middle “C” fundamental frequency is about 261 Hertz. Thus the ideal source is caused to generate notes that have a fundamental frequency ranging from 0 to 261 Hertz. In one embodiment, each note (mechanically generated acoustic sound) is sampled (at step  74 ) using a digital sampling technique where the sampling rate is at least two times the fundamental frequency of the note to be sampled. In another embodiment the sampling rate is greater than two times the fundamental frequency to also sample harmonics of the generated note. 
     The digital samples representing the note produced by the ideal source are then stored at step  76 , in particular in the controller&#39;s memory  54  in the exemplary embodiment  40 . Steps  72 ,  74  and  76  are repeated until all the notes to be generated have been sampled (step  78 ). FIG. 6 is flowchart of an algorithm  80  for enhancing the perceived sound quality of device  10  by employing the samples generated and stored in algorithm  70 . In step  82 , an indication that device  10  is generating or in the process of generating one or more particular notes is received. In the enhanced device  100 , the note detection system  42  is key sensing system that determines when one or more keys of the piano&#39;s  10  keyboard  12  have been depressed or struck. Once a key is struck in a piano there is a delay (mechanical) before acoustic sound is propagated from the string to the soundboard and ultimately to a listener. An exemplary key sensing system is fully described in U.S. Pat. No. 5,001,339, which is assigned to the assignee of this invention and incorporated herein by reference. This key sensing system  42  employs opto-electronic sensors that generate a signal indicative of the displacement and the velocity of each struck or depressed key. These signals are provided the controller  44  via signal line  42 . 
     In the exemplary embodiment not all notes of the device  10  are enhanced, in particular (for the piano) only notes having a fundamental frequency from 0 to about 261 Hertz are enhanced. The algorithm  84  evaluates the struck key indications to whether one or more of its corresponding notes are within the frequency spectrum of notes to be enhanced, i.e., in the piano embodiment having a fundamental frequency between 0 and 261 Hertz. In the device  100 , the controller  44  scans the line  43  for struck key/notes signals and determines whether their corresponding fundamental frequency is within the frequency spectrum to be enhanced. When a note is within the enhancement frequency spectrum, the processor  52  retrieves the digital samples from the memory  54  representing the corresponding ideal source sampled note. Then the gain or energy of these samples are adjusted (step  88 ) based on the user selected gain (user control panel  56 ). 
     FIGS. 4A to  4 D are examples of various embodiments of gain according the present invention. In the embodiments shown in FIGS. 4A to  4 C, the gain across the notes to be enhanced is linearly reduced (on decibel dB scale). When a user increases or lowers the gain of the enhancement, the gain adjustment applies across the range of notes to be enhanced so the gain of all notes are reduced or increased based on the linearly decreasing amplification curve. FIG. 4B, for example, illustrates a medium level gain selection for the amplification curve  64 . The lowest frequency samples (when generated) have about a 10 dB gain while frequency samples (having fundamental frequency) approaching 261 Hertz have very little gain. FIG. 4A illustrates a high level gain selection for the amplification curve  62 . The lowest frequency samples (when generated) have about a 20 dB gain while frequency samples (having fundamental frequency) approaching 261 Hertz have very little gain. FIG. 4C illustrates a low level gain selection for the amplification curve  66 . The lowest frequency samples (when generated) have about a 5 dB gain while frequency samples (having fundamental frequency) approaching 261 Hertz have very little gain. FIG. 4D illustrates a variable amplification curve  68  where the enhancement extends to frequencies beyond 436 Hertz and is non-linear. Other amplification curves may be employed in the present invention. The gain modified samples are provided as an input to a synthesizer/DSP  58  (step  92 ). 
     The synthesizer  58  converts the samples into an analog signal. It is further amplified and converted into acoustic sound via subwoofer/amplifier  46  and cable  45 . In one embodiment the synthesizer  58  is conventional, such as the synthesizer described in U.S. Pat. No. 4,953,437, which is assigned to the assignee of this invention and which is incorporated herein by reference. The subwoofer is a high quality electromechanical transducer, in particular a speaker that accurately reproduces lower frequency analog signals. A different frequency range speaker or a plurality of speakers having different optimal ranges may be employed depending on the frequency range of the enhancement notes to be generated. Generally, the subwoofer speaker  46  emits sounds from both the front and rear of a cone. In one embodiment the speaker acoustic beam emitted from the cone front is oriented towards to a listener and the acoustic beam emitted from the cone rear is oriented towards to the soundboard. It is noted that using the present invention effectively lengthens the strings of piano in which is employed. For example, when the piano&#39;s  10  four foot D string is vibrated, the samples corresponding to the vibrated seven-foot long D string of a concert grand piano is produced by the synthesizer  58  and emitted from the subwoofer  46 . The synthetically-produced sound of the seven-foot D string then melds with the mechanically, acoustically produced sound of the piano&#39;s  10  four-foot D string, thereby effectively lengthening the string in the acoustic piano. 
     While this invention has been described in terms of a best mode for achieving this invention&#39;s objectives, it will be appreciated by those skilled in the art that variations may be accomplished in view of these teachings without deviating from the spirit or scope of the present invention. For example, the present invention may be implemented using any combination of computer programming software, firmware or hardware. As a preparatory step to practicing the invention or constructing an apparatus according to the invention, the computer programming code (whether software or firmware) according to the invention will typically be stored in one or more machine readable storage mediums such as fixed (hard) drives, diskettes, optical disks, magnetic tape, semiconductor memories such as ROMs, PROMs, etc., thereby making an article of manufacture in accordance with the invention. The article of manufacture containing the computer programming code is used by either executing the code directly from the storage device, by copying the code from the storage device into another storage device such as a hard disk, RAM, etc. or by transmitting the code on a network for remote execution.