Abstract:
Disclosed herein are an audio processing apparatus and method. In an embodiment, if a playing mode that abruptly changes the level of audio being played has been input, the data of the audio is processed to mitigate the abrupt change in the level of the audio and converted into analog signals, and the analog signals are output. In an embodiment, if a playing mode that causes a jump from the current track of the audio being played to another track is input, the audio data is divided by an exponential function of 2 before the jump to the another track is completed. In another embodiment, if a playing mode that rapidly moves a playing position to another location on the same track has been input, the audio data is divided by a specific exponential function, and is then multiplied by the exponential function after the playing mode has been completed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to audio processing and, more particularly, to an apparatus and method for eliminating pop noises that are generated when playing conditions are changed during the playing of audio. 
     2. Description of the Related Art 
       FIG. 1  illustrates the construction of a circuit for eliminating pop noises in conventional audio equipment. 
     The pop noise elimination circuit, as illustrated in  FIG. 1 , includes a power signal unit  100  for detecting the application and cutoff of power Vcc and generating a noise elimination drive signal for a predetermined period, a switching signal unit  102  for outputting a noise elimination drive signal in response to a signal that is generated when a mode or source is switched, a pop noise elimination unit  104  for receiving the noise elimination drive signal from the power signal unit  100  or switching signal unit  102  and grounding the output terminal of an audio input unit  103 , and the audio output unit  103  connected to an audio output device AO. 
     The power signal unit  100  includes a condenser C 2  configured to receive power Vcc via a resistor R 1  and be charged with the power Vcc, a diode D 1  connected in parallel to the resistor R 1  in the reverse direction, a condenser C 3  configured to receive the power Vcc via a diode D 2  and be charged with the power Vcc, a transistor TR 1  configured such that the charge voltage of the condenser C 2  is applied to the base thereof, the charge voltage of the condenser C 3  is applied to the emitter thereof and, thus, a noise elimination drive signal is output via the collector thereof, a ground resistor R 3  connected to the collector of the transistor TR 1 , and a diode D 3  configured to output a signal from a node N 3  of the collector of the transistor TR 1  and the ground resistor R 3 . The resistance value of the resistor R 1  is set well above the resistance value of the resistor R 2 . 
     The switching signal unit  102  is configured to receive a switching signal via a General Purpose Input/Output (GPIO) control terminal and output a noise elimination drive signal via a resistor R 4  and a diode D 4 . 
     The audio output unit  103  is configured to output an audio signal, which is received from an audio signal input device AI, to the audio output device AO via a buffer B 1  and a Direct Current (DC) coupling condenser C 1 . 
     The pop noise elimination unit  104  is formed of a transistor TR 2  that receives a noise elimination drive signal from the power signal unit  100  and/or the switching signal unit  102  and grounds the output terminal of the audio output unit  103  connected to the input terminal of the audio output device AO. 
     The operation of the pop noise elimination circuit of  FIG. 1  is described below. 
     When power Vcc is applied, the power Vcc charges the condenser C 2  via the resistor R 1 , which has a high resistance value, so that the charge voltage of the node  1  N 1  slowly increases. In contrast, the power Vcc charges the condenser C 3  via the diode D 2  and the resistor R 2 , which has a small resistance value, so that the charge voltage of node  2  N 2  rapidly increases. 
     The transistor TR 1  is electrically conductive for a predetermined period corresponding to a charge time-constant period, after which the charge voltage of the condenser C 2  reaches a predetermined level, so that a noise elimination drive signal is output through the collector thereof to a node  3  N 3 . Since the noise elimination drive signal is applied to the base of the transistor TR 2  and makes the transistor TR 2  conductive, the audio output device AO is grounded via the transistor TR 2 , therefore pop noises generated while the power Vcc is applied are eliminated. 
     When the voltage of the condenser C 2  reaches a predetermined level after a predetermined period, the transistor TR 1  becomes closed, so that a low potential signal based on a ground potential is output from the node  3  N 3 , that is, the collector of the transistor TR 1 . Accordingly, the transistor TR 2  is closed, so that audio signals from the audio input device AI are normally output to the audio output device AO. 
     Meanwhile, when the power Vcc is cut off, the charge voltage of the condenser C 2  is rapidly discharged through the diode D 1 , and the node  1  N 1  enters a low state. Since the voltage of the condenser C 3  is not discharged by the diode D 2  connected in the reverse direction, the transistor TR 1  becomes conductive. 
     As a result, the charge voltage of the condenser C 3  is discharged through the transistor TR 1  and the resistor R 3 , so that a high potential signal, that is, a noise elimination drive signal, is output from the node  3  N 3  for a predetermined period corresponding to a discharge time-constant period, and the high-potential noise elimination drive signal makes the transistor TR 2  conductive through the diode D 3 , therefore pop noises generated while the power Vcc is cut off are eliminated. 
     Meanwhile, when a mode or source is switched, high-potential switching signal is applied for a predetermined period via the switching signal input terminal of the switching signal unit  102 . 
     The node  4  N 4  is at a high state for the predetermined period and the transistor TR 2  becomes conductive, so that the audio output device AO is grounded for the predetermined period, therefore pop noises generated while a mode or source is switched are eliminated. 
     The conventional pop noise elimination apparatus has both the problem of having a large system size, and the problem of the degradation of trustworthiness of a digital amplifier due to the repetition of high-speed switching. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an apparatus and method for efficiently eliminating pop noises. 
     In order to accomplish the above object, the present invention provides an audio processing method, including the steps of determining whether a playing mode that abruptly changes the level of audio being played has been input; and processing data of the audio so as to mitigate the abrupt change in the level of the audio if the playing mode has been input. 
     In order to accomplish the above object, the present invention provides an audio processing apparatus, including a signal processing unit for performing signal processing on audio data; a digital-analog converter for converting the processed audio data into analog signals and outputting the analog signals; and a control unit for determining whether a playing mode that abruptly changes the level of audio being played has been input, and controlling the signal processing unit so as to mitigate the abrupt change in the level of the audio if the playing mode has been input. 
     Preferably, the playing mode may be a track skip mode or an audio file change mode that causes a jump from a current track of the audio being played to another track, and the audio data may be divided by a specific exponential function before the jump to the another track is completed. 
     Preferably, the playing mode may be a playing mode that rapidly moves a playing position to another location on the same track, and the audio data may be divided by an exponential function of 4, and may be multiplied by the exponential function of 4 after the playing mode has been completed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates the construction of a circuit for eliminating pop noises in conventional audio equipment; 
         FIG. 2  is a block diagram illustrating an apparatus for eliminating pop noises according to an embodiment of the present invention; 
         FIG. 3  illustrates an embodiment of the present invention in which the PCM data of audio is differently processed according to the selected playing mode so as to eliminate pop noises; and 
         FIG. 4  is a flowchart illustrating the operation of a method of eliminating pop noises according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference now should be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components. 
     Preferred embodiments of an apparatus and method for eliminating pop noises according to the present invention are described in detail with reference to the accompanying drawings. 
     When playing conditions or a playing mode is changed by a user during the playing of audio, the level of the audio being played abruptly changes, so that a noise called a pop noise may be generated. For example, this is the case where the manipulation of skipping to a subsequent track (track skip), the manipulation of changing the file being played, or the manipulation of rapidly moving a playing position to another location on the same track (seek mode) is performed by the user while audio is played on a specific track. 
     Accordingly, the change of playing conditions, which may cause a pop noise, during the playing of audio can be detected, and the abrupt change of the level of the PCM data of the audio, that is, the pop noise, can be prevented. 
       FIG. 2  is a block diagram illustrating an apparatus for eliminating pop noises according to an embodiment of the present invention. 
     The pop noise elimination apparatus includes a control unit  208  for controlling the operation of the entire apparatus and predicting pop noises, a decoding unit  200  for preventing pop noises from being generated in the PCM data of audio using a prediction signal transmitted from the control unit  208 , and a Digital-Analog Converter (DAC)  210  for converting pop noise-free PCM data, which is output from the decoding unit  200 , into analog signals and outputting the analog signals. 
     The decoding unit  200  includes a first buffer  202  for storing the PCM data of audio being played, a data processing unit  204  for receiving a pop noise prediction signal from the control unit  208  and eliminating pop noises from the PCM data stored in the first buffer  202 , and a second buffer  206  for storing and outputting pop noise-free PCM data output from the data processing unit  204 . 
     The control unit  208  transmits a prediction signal providing notification of the generation of pop noises to the decoding unit  200  as the user changes playing conditions or selects a playing mode. 
     The decoding unit  200  receives a prediction signal from the control unit  208 , eliminates pop noises from the PCM data using a predetermined method, and outputs pop noise-free PCM data. 
     The first buffer  202  of the decoding unit  200  stores the PCM data of input audio, and transmits the PCM data to the data processing unit  204 . The data processing unit  204  eliminates pop noises by decreasing and/or increasing the PCM data stored in the first buffer  202  using a predetermined method based on the pop noise prediction signal transmitted from the control unit  208 , and transmits pop noise-free PCM data to the second buffer  206 . The second buffer  206  stores the pop noise-free PCM data transmitted from the data processing unit  204 . 
     The DAC  210  converts the PCM data, which is stored in the second buffer  206 , into analog signals, and outputs the analog signals. 
     The operation of the pop noise elimination apparatus according to the present invention, which is illustrated in  FIG. 2 , is described below. 
     When the user selects a certain playing mode during the playing of audio, the level of the PCM data of audio being played abruptly changes, therefore a pop noise may occur. The control unit  208  realizes the selected playing mode and, at the same time, transmits a prediction signal predicting the occurrence of a pop noise to the decoding unit  200  as the user selects the playing mode. 
     In this case, as the playing mode is selected, the level of neighboring data is abruptly changed, so that PCM data including the pop noise can be stored in the first buffer  202  of the decoding unit  200 . 
     Furthermore, the data processing unit  204  eliminates the pop noise by dividing the PCM data including the pop noise, which is stored in the first buffer  202 , by an exponential function and, thus, decreasing the level when receiving the prediction signal from the control unit  208 , and transmitting pop noise-free PCM data to the second buffer  206 . 
     The second buffer  206  stores the pop noise-free PCM data transmitted from the data processing unit  204 , and the DAC  210  converts the PCM data, which is stored in the second buffer  206 , into analog signals and outputs the analog signals. 
     In the meantime, if playing conditions or a playing mode has not been changed during the playing of audio, the decoding unit  200  stores the PCM data of input audio in the second buffer  206  without the operation for eliminating pop noises. 
     The PCM data of audio stored in the first buffer  202  of the decoding unit  200  is processed by the data processing unit  204  using a predetermined method, and is transmitted to the second buffer  206 . 
       FIG. 3  illustrates an embodiment of the present invention in which the PCM data of audio is differently processed according to the selected playing mode so as to eliminate pop noises. 
     As illustrated in  FIG. 3 , in the case where a track skip mode or file change mode, which corresponds to a file skip mode, is selected by the user during the playing of a certain audio file (see (a)), the data processing unit  204  eliminates a pop noise (a 1 ) attributable to the level difference of the PCM data by dividing the PCM data by, for example, the exponential function of 2 and, thus, making the level approach 0 (see (a 2 )), and performing playing while gradually increasing the level of the PCM data, which has been made to approach 0, when detecting the start bit of a new audio file stream. 
     Meanwhile, in the case where a seek mode, which rapidly moves a playing position to another location on the same track, is selected by the user during the playing of a certain track of the audio (see (b)), the data processing unit  204  makes the level of the PCM data approach 0 by dividing the PCM data by, for example, an exponential function of 4 so as to eliminate a pop noise (b 1 ) attributable to the level difference of the PCM data, and gradually increases the level of the PCM data by multiplying the PCM data by an exponential function of 4 when the user terminates the seek mode (see (b 2 )). 
       FIG. 4  is a flowchart illustrating the operation of a method of eliminating pop noises according to an embodiment of the present invention. 
     If the user has selected a certain playing mode at step S 400 , the control unit  208  determines whether the selected playing mode is a track skip mode or file change mode at step S 402 . 
     If the playing mode selected by the user is a track skip mode or file change mode at step S 402 , the control unit  208  transmits a prediction signal, indicating that pop noises would be generated due to the track skip mode or file change mode, to the data processing unit  204 , and the data processing unit  204  makes the PCM data approach 0 by dividing the PCM data of audio including the pop noises, which is stored in the first buffer  202 , by an exponential function of 2 at step S 404 . 
     The data processing unit  204  detects a start bit included in the frame of a new audio file, gradually increases the level of the PCM data made to approach 0, and outputs normal PCM data at step S 406 . 
     Furthermore, if the playing mode selected by the user at step  402  is not a track skip mode or file change mode, the control unit  208  determines whether the playing mode selected by the user is a seek mode at step S 408 . 
     If the playing mode selected by the user is a seek mode, the control unit  208  transmits a prediction signal, indicating that pop noises would be generated due to the seek mode, to the data processing unit  204 . 
     The data processing unit  204  receives a pop noise prediction signal according to the seek mode from the control unit  208 , and makes the PCM data of the audio, including the pop noises, which has been stored in the first buffer  202 , approach 0 by dividing the PCM data by an exponential function of 4 at step S 410 . 
     The control unit  208  detects the termination of the seek mode by the user, and transmits information about the termination of the seek mode to the data processing unit  204 . Accordingly, the data processing unit  204  performs output while increasing the level of the PCM data by multiplying the PCM data, which has been stored in the first buffer  202 , by the exponential function of 4 at step S 412 . 
     The DAC  210  converts the PCM data, from which the pop noise has been eliminated at step S 406  or S 412  and stored in the second buffer  206 , into analog signals, and outputs the analog signals at step S 414 . 
     The present invention may be applied to audio players, such as Compact Disc/Digital Versatile Disc (CD/DVD) players, Moving Picture Experts Group-1/2 Audio Layer-3 (MP3) players and Portable Multimedia Players (PMPs), that are capable of playing audio media, such as CDs and DVDs and/or audio files, such as MP3 files, Ogg files and WMA files. 
     According to the present invention, pop noise causing discomfort can be efficiently eliminated, and the problems with the prior art, that is, the large volume of a system and the repetition of high-speed switching, can be solved. 
     Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.