JP2010072629A - Sequence data output device, voice processing system, and electronic musical instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sequence data output device and a voice processing system, superimposing information which indicates timing for embedding sequence data with high accuracy, without depending on content of an audio signal. <P>SOLUTION: A reference clock creation section 17 obtains, for example, tempo information according to a performance tempo (a set tempo), and generate a reference clock. A timing calculation section 18 obtains performance information from a performance information acquiring section 12, and obtains the reference clock from the reference clock generation section 17. The timing calculation section 18 calculates time difference between performance start timing and performance information acquiring timing by difference from the reference clock, and outputs it to a data superimposing section 15 as an offset value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sequence data output device that outputs a control signal generated by a player's operation input together with an audio signal at an accurate timing.

  Conventionally, techniques for embedding various data in an audio signal have been proposed. For example, Patent Document 1 proposes a technique for embedding data in an audio signal using a digital watermark for the purpose of copyright protection.

  Patent Document 2 proposes a technique for embedding a control signal in an audio signal in time series using a digital watermark.

JP 2006-251676 A JP 2006-323161 A

  However, in the method of Patent Document 1, no consideration is given to the timing of embedding information. Therefore, for example, when there is a silent part, there is a problem in that information cannot be superimposed, and information is superimposed with a large deviation from the timing to be actually embedded.

  On the other hand, in Patent Document 2, the time difference from the head of the audio signal is embedded, and in order to use the control signal at the time of reproduction, it is necessary to always read from the head. Further, the method described in Patent Document 2 requires that a table (code list) showing the relationship between the timing of the control signal and the timing of performance be prepared in advance, so that the performer can randomly (in real time) ) It cannot be used when performing performance operations. Furthermore, the method of Patent Document 2 embeds control signals in units of frames and cannot be used when high resolution (for example, several msec or less) is required as in musical instrument performance.

  Accordingly, an object of the present invention is to provide a sequence data output apparatus and a sound processing system that superimpose information indicating the timing of embedding sequence data with high accuracy without depending on the content of an audio signal.

  The sequence data output device according to the present invention comprises output means for outputting an audio signal generated in response to a performance operation of the performer. In the audio signal, the reference clock and sequence data (performance information and control information of the external device) operated by the performer are superimposed on a band higher than the frequency component of the audio signal. When tempo information is used as a reference clock, the tempo information is superimposed as beat information (tempo clock) such as a MIDI clock. This beat information is always output by, for example, an automatic performance system (sequencer). Furthermore, information related to the time difference between the sequence data superimposition timing and the reference clock is also superimposed on the audio signal in a band higher than the frequency component of the audio signal.

  Therefore, the sequence data output device can include (output with one line) information relating to the reference clock, sequence data, and time difference included in the audio signal. Further, since the output audio signal can be handled in the same manner as a normal audio signal, it can be recorded by a recorder or the like and used as general-purpose audio data. Also, when tempo information is used as the reference clock, the time difference between the tempo clock and the timing at which the sequence data is superimposed is embedded in the audio signal, so that the sequence data is MIDI data (performance information). Thus, synchronization with an existing automatic performance device is possible. Further, by correcting the time difference from the reference clock, it is possible to correct performance information generation delay, mechanical delay until musical tone generation, and the like in real time.

  In the present invention, since the time difference from the reference clock generated at regular intervals is superimposed, it is not necessary to read from the head of the audio signal, and information about the time difference can be embedded with high resolution. For example, when the information regarding the time difference is expressed as a difference (offset value) from the immediately preceding reference clock, the reference clock having a period of about 740 msec, which is a period when the M-sequence signal of 2047 points is oversampled 16 times at a sampling frequency of 44.1 kHz. On the other hand, if the offset value is 8 bits, a resolution of about 3 msec can be obtained, and it can be used for a musical instrument performance requiring a high resolution.

  The sequence data output device superimposes and outputs the information so as to include a modulation component of information to be superimposed on a band higher than the frequency component of the audio signal generated according to the performance operation (for example, information on the time difference). . For example, it is possible to encode the M-sequence pseudo noise (PN code) by phase-modulating the information regarding the time difference. The frequency band for superimposing the information on the time difference is desirably a non-audible range of 20 kHz or more. However, in the case where the non-audible range cannot be used due to D / A conversion or encoding of compressed audio, for example, a high frequency of 15 kHz or more. Superimpose information on time difference in the band to reduce the effect on hearing. For the sequence data and tempo information, the same superposition method as that for the information regarding the time difference can be used.

  In the above invention, the sequence data may be generated in accordance with a player's operation input. In this case, the difference between the operation input timing (for example, musical sound generation timing) and the sequence data superimposition timing is superimposed.

  Note that the sequence data output device is an aspect built in an electronic musical instrument such as an electronic piano, an aspect in which an audio signal is input from an existing musical instrument, an aspect in which an acoustic signal or singing sound is collected by a microphone and an audio signal is input. , Etc.

  In addition, an aspect in which the speech data processing system further includes a decoding device that decodes the sequence data using the sequence data output device according to claim 1 or 2 is also possible.

  In this case, the decoding apparatus buffers the audio signal or previously decodes various information from the audio signal, and synchronizes the audio signal and the sequence data based on the decoded reference clock and offset value.

  The superimposing means of the sequence data output device superimposes the reference clock by superimposing pseudo noise on the audio signal at a timing based on the reference clock. As the pseudo noise, a signal having high autocorrelation such as a PN code is used. When tempo information is used as the reference clock, the sequence data output device generates a signal with high autocorrelation at a timing based on the performance tempo (for example, for each beat) and superimposes it on the audio signal. Therefore, even if sound is output as an analog audio signal, the superimposed tempo information is not lost.

  The decoding device includes input means for inputting the audio signal and decoding means for decoding the reference clock. The decoding unit obtains a correlation between the audio signal input to the input unit and the pseudo noise, and decodes the reference clock based on the peak generation timing of the correlation. Since the pseudo noise superimposed on the audio signal is a signal having a very high autocorrelation, when a correlation between the audio signal and the pseudo noise is obtained by the decoding device, a correlation peak of a certain period is extracted. Therefore, the correlation peak generation timing indicates the reference clock.

  Pseudo noise with high autocorrelation such as PN code can extract the peak of correlation even at low level, so it is highly accurate even though it is sound that is not uncomfortable on hearing (sound that is difficult to hear). Tempo information can be superimposed and decoded. Further, if pseudo noise is superimposed only on a high frequency band of 20 kHz or higher, it is possible to make it more difficult to hear.

  According to the present invention, it is possible to superimpose information indicating the timing of embedding sequence data with high accuracy without depending on the content of the audio signal.

It is a figure which shows the structure of the speech processing system which concerns on embodiment of this invention. It is a figure which shows the structure of a data superimposition part and a timing extraction part. It is the figure which showed the example of the data superimposed on an audio signal, and the relationship between a reference clock and an offset value. It is the figure which showed the other example of the data superimposed on an audio signal. It is a figure which shows an example in case performance start timing is later than performance information recording timing.

  FIG. 1 is a diagram showing a configuration of a speech processing system according to an embodiment of the present invention. The voice processing system includes a sequence data output device and a decoding device. FIG. 1A shows an example in which an electronic musical instrument (electronic piano) also serves as a device that outputs tempo information serving as a reference clock. In the present embodiment, an example in which performance information is superimposed on an audio signal as sequence data will be described.

  1A includes a control unit 11, a performance information acquisition unit 12, a musical tone generation unit 13, a reference clock superimposition unit 14, a data superposition unit 15, an output interface (I / F) 16, and a reference clock generation. A unit 17 and a timing calculation unit 18 are provided.

  The performance information acquisition unit 12 acquires performance information according to the performance operation of the performer. The acquired performance information is output to the tone generator 13 and the timing calculator 18. The performance information includes, for example, information on the pressed keyboard (note number), timing of key pressing (note on, note off), speed of pressing the keyboard (velocity), and the like. Which performance information is output (which music information is used to generate a musical sound) is instructed by the control unit 11.

  The musical sound generator 13 has a built-in sound source, and generates musical sounds (audio signals) by inputting performance information from the performance information acquisition unit 12 in accordance with an instruction (setting of a volume or the like) from the control unit 11. The audio signal of the present invention is not limited to an analog signal, and may be a digital signal.

  The reference clock generation unit 17 generates a reference clock corresponding to the set tempo. When the tempo clock is used as the reference clock, the tempo clock is, for example, a clock that conforms to a MIDI clock (24 clocks per quad note) and is always output. The reference clock generation unit 17 outputs the generated reference clock to the reference clock superimposition unit 14 and the timing calculation unit 18.

  Note that a metronome sound generating section that generates a metronome sound according to the tempo clock may be provided, and the metronome sound may be mixed with a musical sound by performance and output from a headphone I / F or the like. In this case, the performer can perform while listening to the metronome sound (tempo) heard from the headphones.

  The electronic piano 1 is provided with an operator dedicated to inputting tempo information (a tap switch or the like, a tempo information input unit indicated by a broken line in the figure), and a beat engraved by the performer is input as a reference tempo signal to extract tempo information. It is also possible to configure.

  The reference clock superimposing unit 14 superimposes the reference clock on the audio signal input from the musical sound generating unit 13. The superimposing method uses a technique that makes it difficult to hear the superimposed signal. For example, pseudo noise such as a PN code (M series) is superimposed at a weak level that does not cause a sense of discomfort. At this time, the band on which the pseudo noise is superimposed may be limited to a band outside the audible range (20 kHz or more). In the case of a configuration in which a non-audible range cannot be used due to D / A conversion, compressed audio encoding, or the like, the audible influence can be reduced even in a high frequency band of 15 kHz or higher, for example. Since pseudo-noise such as M-sequence has very high autocorrelation, the reference clock can be extracted by obtaining the correlation between the audio signal and the same code as the pseudo-noise superimposed on the decoding side. it can. In addition, you may use other random numbers, such as not only M series but Gold series.

  The reference clock extraction process on the decoding side will be described with reference to FIG. 1B and FIG. The decoding device 2 shown in FIG. 2B has a function as a recorder that records an audio signal, a function as a player that reproduces the audio signal, and a decoder that decodes a reference clock superimposed on the audio signal. As a function. Here, the function of decoding the reference clock superimposed on the audio signal will be mainly described with respect to the decoding device 2 shown in FIG.

  1B, the decoding device 2 includes an input I / F 21, a control unit 22, a storage unit 23, a reference clock extraction unit 24, and a timing extraction unit 25. The control unit 22 records the audio signal input from the input I / F 21 and records it as general-purpose audio data in the storage unit 23. In addition, the control unit 22 reads the audio data recorded in the storage unit 23 and outputs it to the reference clock extraction unit 24.

  The reference clock extraction unit 24 generates the same pseudo noise as the pseudo noise generated by the reference clock superimposing unit 14 of the electronic piano 1 and obtains a correlation with the reproduced audio signal. Since the pseudo noise superimposed on the audio signal is a signal having a very high autocorrelation, when the correlation between the audio signal and the pseudo noise is obtained, as shown in FIG. Peaks are extracted. This correlation peak generation timing indicates the reference clock.

  When tempo information is used as the reference clock, the beat timing and the bar timing can be distinguished on the decoding side by superimposing a plurality of different pseudo noises at the beat timing and the bar timing. In this case, it is preferable to provide a plurality of tempo clock extraction units for beat timing extraction and measure timing extraction. By superimposing different patterns of pseudo-noise at beat timing and measure timing, the beat timing and measure timing can be superimposed and decoded separately with high accuracy without interfering with each other's pseudo-noise.

  The reference clock extracted as described above can be used for automatic performance by a sequencer as long as it conforms to tempo information such as MIDI clock. For example, an automatic performance reflecting its own performance tempo can be realized by a sequencer.

  In FIG. 1A, the reference clock superimposing unit 14 generates a pseudo-noise of a predetermined length and superimposes it on the audio signal every time the reference clock is input from the reference clock generating unit 17 and outputs it to the data superimposing unit 15. To do. The timing calculation unit 18 acquires performance information from the performance information acquisition unit 12 and outputs the performance information to the data superimposition unit 15.

  The data superimposing unit 15 superimposes performance information on the audio signal input from the reference clock superimposing unit 14. At this time, the timing calculation unit 18 calculates a time difference between the reference clock and the performance information superimposition timing in the data superimposition unit 15, and outputs information related to the time difference to the data superimposition unit 15 together with the performance information. Information regarding the time difference is represented by a difference (offset value) from the reference clock. The timing calculation unit 18 converts the data into a predetermined data format and outputs the data to the data superimposition unit 15 so that the performance information and the offset value can be superimposed on the audio signal (see FIG. 3A). ).

  The data superimposing unit 15 superimposes the performance information and the offset value input from the timing calculating unit 18 on the audio signal. In the superimposing method, a high frequency carrier signal is phase-modulated with performance information or an offset value (a data code string of 0, 1) so that a modulation component is in a band different from the frequency component (acoustic signal component) of the audio signal. To be included. It is also possible to use the following spread spectrum.

  FIG. 2A is a block diagram illustrating an example of the configuration of the data superimposing unit 15 when using spread spectrum. In the figure, all digital signal processing is described, but the signal output to the outside may be an analog signal (signal after analog conversion).

  In this example, the multiplier 155 multiplies the M-sequence pseudo noise code (PN code) output from the spread code generator 154 by the performance information and the offset value (which is a data code string of 0 and 1). Spread spectrum of the data code string. The spread data code string is input to the XOR circuit 156. The XOR circuit 156 outputs an exclusive OR of the code input from the multiplier 155 and the output code one sample before input via the delay unit 157, and differentially encodes the spread data code string. The signal after differential encoding is binarized by -1,1. By outputting the differential code binarized to −1 and 1, the decoding side can extract the data code string after spreading by multiplying the differential code of two consecutive samples.

  The differentially encoded data code string is band-limited within the baseband by an LPF (Nyquist filter) 158 and input to the multiplier 160. Multiplier 160 multiplies the carrier signal output from carrier signal generator 159 (carrier signal higher in frequency than the acoustic signal component) and the output signal of LPF 158, and frequency-shifts the data code string after differential encoding to the passband. To do. The data code string after differential encoding may be frequency shifted after up-sampling. The data code string after the frequency shift is gain-adjusted by the gain adjuster 161, mixed with the audio signal by the adder 153, and output to the output I / F 16.

  The audio signal output from the reference clock superimposing unit 14 is cut in the passband band by the LPF 151 and gain-adjusted by the gain adjuster 152 and then input to the adder 153. However, the LPF 151 is not essential. It is not necessary to completely divide the band of the acoustic signal component and the modulation signal component (the frequency component of the superimposed data code string). For example, if the carrier signal is set to about 20 to 25 kHz, even if the acoustic signal component and the modulated signal component are slightly overlapped, the SN ratio is such that the listener can hardly hear the modulated signal and can decode the data code string. Can be secured. Note that the frequency band for superimposing the data code string is desirably a non-audible range of 20 kHz or more. However, in the case where the non-audible range cannot be used by D / A conversion, compression audio encoding, or the like, for example, a frequency band of 15 kHz or more is used. By superimposing the data code string on the high frequency band, the influence on hearing can be reduced.

  As described above, the audio signal on which the data code string (performance information and offset value) and the reference clock are superimposed is output from the output I / F 16 which is an audio output terminal.

  In the decoding device 2, the reference clock extraction unit 24 decodes the reference clock as described above, and the timing extraction unit 25 decodes the performance information and the offset value superimposed on the audio signal. When the above-described spread spectrum is used, it is performed as follows.

  FIG. 2B is a block diagram illustrating an example of the configuration of the timing extraction unit 25. The audio signal input to the timing extraction unit 25 is input to the HPF 251. The HPF 251 is a filter for removing acoustic signal components. The output signal of the HPF 251 is input to the delay unit 252 and the multiplier 253. The delay amount of the delay unit 252 is set to a time corresponding to one sample of the differential code. When the differential code is upsampled, it is set to the time for one sample after the upsampling. The multiplier 253 multiplies the signal input from the HPF 251 by the signal one sample before output from the delay unit 252 and performs delay detection processing. The differentially encoded signal is binarized to −1 and 1, and indicates the phase change from the code one sample before. Therefore, by multiplying the signal one sample before, the difference is obtained. The performance information before dynamic coding and the offset value (spread code) are extracted.

  The output signal of the multiplier 253 is extracted as a baseband signal through the LPF 254 that is a Nyquist filter, and is input to the correlator 255. The correlator 255 obtains the correlation with the input signal using the same spreading code as the spreading code output from the spreading code generator 254. Since the spreading code uses a PN code with high autocorrelation, the correlation value output from the correlator 255 is extracted by the peak detector 256 with positive and negative peak components in the spreading code period (data code period). The The code determination unit 257 decodes each peak component as performance information and a data code (0, 1) of an offset value. In this way, the performance information and the offset value superimposed on the audio signal are decoded. Note that the superposition-side differential encoding process and the decoding-side delay detection process are not essential. Also, the reference clock can be superimposed on the audio signal by phase-modulating the spreading code with the reference clock.

  Next, FIG. 3 is a diagram illustrating an example of data superimposed on an audio signal and a relationship between a reference clock and an offset value. First, FIG. 3A shows an example in which the actual performance start timing (musical sound generation timing) matches the performance information recording timing. In this case, the timing calculation unit 18 detects a difference from the immediately preceding reference clock, calculates a time difference (offset value) from the generation of the musical sound, and generates data as shown in FIG.

  As shown in FIG. 3B, the data superimposed on the audio signal includes an offset value and performance information. The offset value represents the time difference (msec) between the performance information recording timing (performance start timing) and the immediately preceding reference clock.

  In the example shown in FIGS. 6A and 6B, the time difference between the performance start timing and the reference clock is 200 msec, so that the offset value = 200. Therefore, the timing calculation unit 18 outputs data including “offset value = 200” information and performance information to the data superimposing unit 15.

  Thus, since the electronic piano 1 outputs the offset value with respect to the reference clock superimposed on the audio signal, information regarding the time difference can be embedded with high resolution. For example, an offset value of 8 bits with respect to a reference clock having a period of about 740 msec, which is a period when an M-sequence signal of 2047 points is oversampled 16 times at a sampling frequency of 44.1 kHz, a high resolution of about 3 msec can be obtained. It is done. Further, since the offset value with respect to the reference clock is recorded as information relating to the time difference, there is no need to read the audio signal from the head on the playback side.

  Next, FIG. 4 is a diagram showing another example of data superimposed on the audio signal. FIG. 4A shows an example in which the data superimposing unit 15 superimposes data with a delay of 7 beats from the performance start timing. The delay from the generation of the musical sound to the data superimposition occurs, for example, when there is a silent section and various information cannot be superimposed or when the delay until the performance information acquisition is large. The timing calculation unit 18 detects the silent section and calculates the time difference from the generation of the musical sound, and generates data as shown in FIG.

  As shown in FIG. 4B, in this example, a reference clock offset value and an in-clock offset value are defined as offset values. The reference clock offset value represents the difference (number of clocks) between the reference clock immediately before the performance information recording timing and the reference clock immediately before the actual performance start timing. The in-clock offset value represents the time difference (msec) between the performance start timing and the reference clock immediately before it.

  In the example shown in FIGS. 6A and 6B, there are 7 clock differences from the reference clock immediately before the performance start timing to the reference clock immediately before the performance information recording timing, so the reference clock offset value = 7. It becomes. Further, since the time difference between the performance start timing and the immediately preceding reference clock is 200 msec, the in-clock offset value = 200. Therefore, the timing calculation unit 18 outputs data including “reference clock offset value = 7, in-clock offset value = 200” information and performance information to the data superimposing unit 15.

  If the delay time from the start of performance to the generation of musical tone is constant, the timing calculation unit 18 may calculate the offset value by always subtracting a constant value from the timing at which the performance information is acquired.

  Further, if the reference clock offset value is 0, information regarding the reference clock offset value is not necessary, and therefore, the example is the same as the example shown in FIGS. 3A and 3B. In actual use, when there are many situations shown in FIGS. 3A and 3B, the presence / absence of the reference clock offset value is defined as a 1-bit flag as follows to reduce the data capacity. It may be.

  That is, as shown in FIG. 4C, a flag indicating the presence / absence of the reference clock offset value is defined at the beginning of the data. When the flag is 0, since the reference clock offset value is 0, only the in-clock offset value as shown in FIG. When the flag is 1, since the reference clock offset value is 1 or more (or -1 or less as will be described later), the reference clock offset value, the in-clock offset value, and the performance information as shown in FIG. Is included.

  Further, as shown in FIG. 5, even when the performance start timing is later than the performance information recording timing (when a future time is designated), the offset value can be calculated and superimposed. In this case, the reference clock offset value may be a negative value (for example, reference clock offset value = −3). For example, it is suitable for a case where a long mechanical delay occurs until an actual musical tone is generated from an instruction to start performance, such as an automatic performance piano. In addition, when the sequence data to be superimposed on the audio signal is control information for controlling an external device (effector, lighting, etc.), when the performer inputs an operation so that the operation starts several seconds ahead And so on.

  Next, how to use the reference clock and the offset value will be described. In FIG. 1B, the audio signal output from the output I / F 16 is input to the decoding device 2. Since the audio signal output from the electronic piano 1 can be handled in the same manner as a normal audio signal, it can be recorded with another general recording device. Further, since the recorded audio data is general-purpose audio data, it can be reproduced by a general audio player.

  The control unit 22 reads the audio data recorded in the storage unit 23 and outputs it to the timing extraction unit 25. The timing extraction unit 25 decodes the offset value and performance information superimposed on the audio signal and inputs them to the control unit 22. Based on the reference clock input from the reference clock extraction unit 24 and the offset value, the control unit 22 synchronizes and outputs the audio signal and performance information to the outside. If a tempo clock is used as the reference clock, the tempo clock may also be output at this time.

  The output audio signal and performance information are used for musical score display and the like. For example, a musical score can be displayed on a monitor based on a note number included in performance information and a musical sound can be emitted to be used as an educational material for practice. It is also possible to perform an automatic performance that is output to a sequencer or the like and synchronized with an audio signal. As described above, since a negative value can be applied as the reference clock offset value, a synchronized performance can be accurately performed even when the performance start timing is later than the performance information recording timing.

  It is desirable that the control unit 22 buffers a certain amount of audio data in a built-in RAM (not shown) and reproduces it, or decodes it in advance and reads out performance information and an offset value in advance. .

  Note that the sequence data output device of the present invention is not limited to a mode built in an electronic musical instrument, and can be attached to an existing musical instrument later. In this case, an audio signal input terminal is provided, and the control signal is superimposed on the audio signal input from the input terminal. For example, you can get an audio signal by connecting an electric guitar with a line output terminal or connecting a normal microphone, or you can get performance information by attaching a sensor circuit on the back. Is possible. Accordingly, the sequence data output device of the present invention can be used even for an acoustic instrument.

1-electronic piano 11-control unit 12-performance information acquisition unit 13-music sound generation unit 14-reference clock superimposition unit 15-data superposition unit 16-output I / F
17-reference clock generator 18-timing calculator

Claims (7)

A reference clock generating means for generating a reference clock at regular intervals;
A reference clock superimposing means for superimposing the reference clock on an audio signal generated in accordance with the performance operation of the performer;
Data superimposing means for superimposing the audio signal sequence data;
A time difference detecting means for detecting a time difference between the sequence data superimposition timing and the reference clock;
An output means for outputting an audio signal on which the reference clock and the sequence data are superimposed by the reference clock superimposing means and the data superimposing means;
With
The data superimposing means superimposes information on the time difference together with the sequence data on the audio signal,
A sequence data output apparatus, wherein a modulation component of information to be superimposed is included in a band higher than a frequency component of the audio signal. Operation input means for inputting a player's operation;
Data generation means for generating the sequence data in response to an operation input of the operation input means,
The time difference detecting means detects a time difference between the operation input timing and the sequence data superimposition timing by a difference from the reference clock, and represents information related to the time difference by the difference. Item 4. The sequence data output device according to Item 1. The data superimposing means includes a spreading code generating unit that generates a spreading code having a predetermined period;
A modulation unit that phase-modulates the spreading code for each period based on superimposition information;
A synthesis unit that synthesizes a modulation signal generated based on the phase-modulated spreading code with the audio signal in a frequency band higher than the frequency of the audio signal, and outputs the synthesized signal;
The sequence data output device according to claim 1 or 2, further comprising: A speech processing system comprising: the sequence data output device according to any one of claims 1 to 3; and a decoding device that decodes information superimposed on the audio signal.
The decoding device includes a synchronization unit that inputs the audio signal in advance and synchronizes the audio signal and the sequence data based on the reference clock and the time difference information decoded from the audio signal. Processing system. The reference clock superimposing means of the sequence data output device superimposes the reference clock by superimposing pseudo noise on the audio signal at a timing based on the reference clock,
The audio processing system according to claim 4, wherein the decoding device includes a decoding unit that obtains a correlation between the audio signal and the pseudo noise and decodes the reference clock based on a peak generation timing of the correlation.   6. The sequence data output device according to claim 1, wherein tempo information reflecting a performance tempo of a performer is used as the reference clock.   An electronic musical instrument incorporating the sequence data output device according to claim 1.

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