JP6604728B2 - Audio processing apparatus and audio processing method - Google Patents

Description

  The present invention relates to a voice processing apparatus and a voice processing method.

  As an apparatus that processes an audio signal, an imaging apparatus that records an image signal and an audio signal is known. Some imaging devices record a sound signal input from a microphone, and at that time, some include a limiter that limits a recording level in case an excessive sound signal is input. Since the limiter limits the recording level by reducing the excessive amplitude of the input signal, harmonics and aliasing distortion occur during operation. For this reason, in order to avoid distortion, a technique is known that limits the bandwidth of an input signal of a limiter (see Patent Document 1).

JP 2010-237294 A

  However, performing band limitation on the input signal limits the band of the recording signal, and there is a problem that the wideband frequency characteristics desired by the user cannot be realized.

An object of the present invention is to provide an audio processing apparatus and an audio processing method capable of preventing aliasing noise caused by a limiter unit without limiting the band of an audio signal.

An audio processing apparatus according to the present invention receives a first audio signal, and outputs an audio signal in a first frequency band and an audio signal in a second frequency band higher than the first frequency band; First limiter means for performing a limiter process on the first frequency band audio signal output from the output means; the second frequency band audio signal output from the output means; possess adding means for adding the output signal from the first limiter means, the output means performs low-pass filtering process on the first audio signal, the audio signal of the first frequency band a low-pass filter means for outputting said audio signal of the first frequency band is subtracted from the first audio signal, characterized by chromatic and subtracting means for outputting an audio signal of the second frequency band .

By performing limiter processing on the audio signal in the first frequency band, aliasing noise by the first limiter means can be prevented without limiting the band of the audio signal.

It is a block diagram showing an example of composition of an imaging device of a 1st embodiment. It is a block diagram which shows the structural example of an audio | voice processing part. It is a figure which shows the signal amplitude of the input / output of an audio | voice processing part. It is a figure which shows the output waveform of an audio | voice processing part. It is a block diagram which shows the structural example of the audio | voice processing part of 1st Embodiment. It is a block diagram which shows the structural example of the audio | voice processing part of 2nd Embodiment.

(First embodiment)
FIG. 1 is a block diagram illustrating a configuration example of an imaging apparatus 100 according to the first embodiment of the present invention. The imaging apparatus 100 includes an audio processing unit (audio processing apparatus) 103 that can process an audio signal. The imaging apparatus 100 includes an imaging unit 101, an audio input unit 102, an audio processing unit 103, a memory 104, a display control unit 105, a display unit 106, and an encoding processing unit 107. Furthermore, the imaging apparatus 100 includes a recording / playback unit 108, a recording medium 109, a control unit 110, an operation unit 111, an audio output unit 112, a speaker 113, an external output unit 114, and a data bus 115.

  The imaging unit 101 converts an optical image of a subject formed by the photographing lens into an image signal by an imaging element, performs analog-digital conversion, image adjustment processing, and the like, and generates image data. The audio input unit 102 collects audio around the imaging device 100 by a plurality of microphones built in or connected via audio terminals, performs analog-digital conversion, audio processing, and the like to generate audio data. The audio processing unit 103 performs audio signal processing on the audio data generated by the audio input unit 102. The memory 104 temporarily stores the image data generated by the imaging unit 101 and the audio data processed by the audio processing unit 104. The display control unit 105 displays the video based on the image data generated by the imaging unit 101, the operation screen of the imaging device 100, the menu screen, and the like on the external display via the display unit 106 and the video terminal. The encoding processing unit 107 reads out image data and audio data temporarily stored in the memory 104, performs predetermined encoding, and generates compressed image data, compressed audio data, and the like. The recording / reproducing unit 108 records the compressed image data and the compressed audio data generated by the encoding processing unit 107 on the recording medium 109, or the compressed image data, the compressed audio data recorded on the recording medium 109, Read various data and programs. Here, the recording medium 109 includes all types of recording media such as a magnetic disk, an optical disk, and a semiconductor memory as long as compressed image data, compressed audio data, and the like can be recorded.

  The control unit 110 can control each block of the imaging apparatus 100 by outputting a control signal to each block of the imaging apparatus 100, and includes a CPU, a memory, and the like for performing various controls. The operation unit 111 includes a button, a dial, and the like, and outputs an instruction signal to the control unit 110 according to a user operation. The encoding processing unit 107 decodes the compressed audio data read by the recording / reproducing unit 108 and generates audio data. The audio output unit 112 outputs the audio data decoded by the encoding processing unit 107 and the audio data output by the control unit 110 to the speaker 113 and the audio terminal. The external output unit 114 outputs the compressed image data and the compressed audio data read by the recording / reproducing unit 108 to an external device. The data bus 115 supplies various data such as audio data and image data and various control signals to each block of the imaging apparatus 100.

  Next, a normal operation of the imaging apparatus 100 according to the present embodiment will be described. The imaging apparatus 100 according to the present embodiment supplies power to each block of the imaging apparatus 100 by the power supply unit in response to the instruction signal for turning on the power by operating the operation unit 111 by the user. When the power is supplied, the control unit 110 instructs the operation unit 111 to indicate which mode, for example, the shooting mode, the playback mode, the moving image recording mode, etc. Check by signal. In the moving image recording mode, the imaging apparatus 100 can record the image data generated by the imaging unit 101 and the audio data generated by the audio input unit 102 on the recording medium 109 as one file. In the reproduction mode, the imaging apparatus 100 can read the compressed image data recorded on the recording medium 109 by the recording / reproducing unit 108, decode it by the encoding processing unit 107, and display it on the display unit 106.

  In the moving image recording mode, first, the control unit 110 outputs a control signal to each block of the imaging apparatus 100 so as to shift to the shooting standby state, and performs the following operation. The imaging unit 101 converts an optical image of a subject imaged by a photographing lens into an image signal by an imaging element, performs analog-digital conversion and image adjustment processing, generates image data, and controls display of the generated image data Output to the unit 105. The display control unit 105 causes the display unit 106 to display the input image data. The user prepares for shooting while viewing the image displayed on the display unit 106.

  The audio input unit 102 converts analog audio signals generated by a plurality of microphones into digital audio signals, and generates a plurality of digital audio signals. The audio processing unit 103 performs arbitrary signal processing on the generated digital audio signal, generates multi-channel audio data, and outputs the generated audio data to the audio output unit 112. The audio output unit 112 outputs the sound to the speaker 113 and the earphone. The user can adjust the manual volume to determine the recording volume while listening to the sound output in this way.

  Next, when a shooting start instruction signal is output to the control unit 110 by the user operating the recording button of the operation unit 111, the control unit 110 outputs a shooting start instruction signal to each block of the imaging apparatus 100. Then, the following operation is performed. The imaging unit 101 converts an optical image of a subject imaged by a photographing lens into an image signal by an imaging element, performs analog-digital conversion and image adjustment processing, generates image data, and controls display of the generated image data Output to the unit 105. The display control unit 105 causes the display unit 106 to display the input image data. Further, the imaging unit 101 stores the generated image data in the memory 104.

  The audio input unit 102 converts analog audio signals generated by a plurality of microphones into digital audio signals, and generates a plurality of digital audio signals. The audio processing unit 103 performs arbitrary signal processing on the generated digital audio signal, generates multi-channel audio data, and stores the generated audio data in the memory 104.

  The encoding processing unit 107 reads out image data and audio data temporarily stored in the memory 104, performs predetermined encoding, and generates compressed image data, compressed audio data, and the like. Then, the control unit 110 synthesizes the compressed image data and the compressed audio data, forms a data stream, and outputs the data stream to the recording / reproducing unit 108. The recording / playback unit 108 writes the data stream to the recording medium 109 as one moving image file under the management of a file system such as UDF or FAT.

  The above operation is continued during shooting. When the user operates the recording button of the operation unit 111 to output a shooting end instruction signal to the control unit 110, the control unit 110 outputs a shooting end instruction signal to each block of the imaging apparatus 100. The following operations are performed. The imaging unit 101 and the audio input unit 102 stop generating image data and audio data, respectively. The encoding processing unit 107 reads the remaining image data and audio data stored in the memory 104, performs predetermined encoding, and stops operation when generation of compressed image data and compressed audio data is completed.

  Then, the control unit 110 combines these final compressed image data and compressed audio data, forms a data stream, and outputs the data stream to the recording / reproducing unit 108. The recording / playback unit 108 writes the data stream to the recording medium 108 as one moving image file under the management of a file system such as UDF or FAT. Then, when the supply of the data stream is stopped, the recording / playback unit 108 completes the moving image file and stops the recording operation. When the recording operation stops, the control unit 110 outputs a control signal to each block of the imaging apparatus 100 so as to shift to the shooting standby state, and returns to the shooting standby state.

  Next, in the reproduction mode, the control unit 110 outputs a control signal to each block of the imaging apparatus 100 so as to shift to the reproduction state, and performs the following operation. The recording / playback unit 108 reads a moving image file composed of compressed image data and compressed audio data recorded on the recording medium 109, and outputs the read compressed image data and compressed audio data to the encoding processing unit 107. The encoding processing unit 107 decodes the compressed image data and the compressed audio data, and outputs them to the display control unit 105 and the audio processing unit 103, respectively. The audio processing unit 103 performs arbitrary signal processing on the generated digital audio signal and outputs audio data to the audio output unit 112. The display control unit 105 causes the display unit 106 to display the decoded image data. The audio output unit 112 outputs the decoded audio data from an external speaker built in or attached.

  As described above, the imaging apparatus 100 of the present embodiment can perform recording and reproduction of images and sounds. By the way, the audio processing unit 103 according to the present embodiment executes limiter processing for limiting the recording level for a plurality of digital audio signals corresponding to the plurality of analog audio signals generated by the microphone.

  FIG. 2 is a block diagram illustrating a configuration example of the audio processing unit 103. Hereinafter, the limiter process of the audio processing unit 103 will be described. The audio processing unit 103 includes a variable gain limiter 201 and a non-linear limiter 202. The gain variable limiter 201 includes an amplification unit 203, a detection unit 204, and an amplification control unit 205. The audio processing unit 103 receives a plurality of input audio signals IN, performs limiter processing, and outputs a plurality of output audio signals OUT. The plurality of input audio signals IN are, for example, a right channel audio signal and a left channel audio signal. The gain variable limiter 201 receives a plurality of input audio signals (second audio signals) IN, performs a limiter process on each of the plurality of input audio signals IN with a variable gain, and outputs a plurality of audio signals (first audio signals). ) Output A1. The detection unit 204 detects the level of the input audio signal IN and outputs the level of the input audio signal IN to the amplification control unit 205. The amplification control unit 205 controls the gain of the amplification unit 203 according to the level detected by the detection unit 204. The amplifying unit 203 amplifies the input audio signal IN with the variable gain controlled by the amplification control unit 205, and outputs the audio signal A1 subjected to limiter processing. The non-linear limiter 202 multiplies the output signal A of the amplifier 203 by a non-linear coefficient and outputs an audio signal OUT.

  FIG. 3 is a diagram illustrating the amplitudes of the output audio signals A1 and OUT with respect to the amplitude of the input audio signal IN. The horizontal axis represents the input audio signal IN, and the vertical axis represents the output audio signals A1 and OUT. The amplitudes of the input audio signal IN and the output audio signals A1, OUT are normalized by 0 dBFS by 1, and the input audio signal IN of +6 dBFS is limited to the output audio signals A1, OUT of 0 dBFS. When the input audio signal IN is larger than −6 dBFS, the non-linear limiter 202 corrects it with a quadratic function and outputs the output audio signal OUT.

  The amplification control unit 205 controls the gain of the amplification unit 203 to be 1 when the level of the input audio signal IN is smaller than the first threshold (normalized value is 1). In this case, the amplifying unit 203 has a gain of 1, does not perform limiter processing, and outputs an output audio signal A1 having the same amplitude as the input audio signal IN. On the other hand, when the level of the input audio signal IN is higher than the first threshold value (normalized value is 1), the amplification control unit 205 sets the output audio signal A1 to a constant value (a limiter value with a normalized value of 1). ), The gain of the amplification unit 203 is controlled. In this case, the amplifying unit 203 performs a limiter process with a gain of less than 1, and limits the amplitude of the output audio signal A1 to a constant value (limiter value).

  When the amplitude of the output audio signal A1 of the amplification unit 203 is smaller than the second threshold (normalized value is 0.6), the non-linear limiter 202 directly uses the output audio signal A1 of the amplification unit 203 as the output audio signal OUT. Output. Alternatively, in this case, the non-linear limiter 202 may output the output audio signal OUT by multiplying the output audio signal A1 of the amplifying unit 203 by the coefficient “1”. On the other hand, when the amplitude of the output audio signal A1 of the amplifying unit 203 is larger than the second threshold (normalized value is 0.6), the non-linear limiter 202 adds a second order to the output audio signal A1 of the amplifying unit 203. The output audio signal OUT is output by multiplying the coefficient of the function.

  FIG. 4 is a diagram showing the waveforms of the output audio signals A1 and OUT. The output audio signal A1 has an acute angle at the portion where the amplitude is clipped at the maximum value, and has a very large number of high frequency components, so the audibility is very poor. On the other hand, the output audio signal OUT has rounded corners where the amplitude is clipped at the maximum value, and the high frequency component is reduced, so that the audibility is improved. This effect is mainly conspicuous with respect to an input audio signal IN having a low frequency of 1 kHz or less. When the frequency of the input audio signal IN exceeds 1 kHz, the harmonic component becomes higher, so that it is audible. Less effective. The cycle in which the gain variable limiter 201 lowers the gain is the sampling frequency of the input audio signal IN, and the gain reduction range is about 0.1 dB per step. If the gain reduction range exceeds 0.1 dB, a discontinuous portion of the output audio signal A1 generated when the gain is changed is heard. Therefore, when the input audio signal IN greatly exceeds the first threshold value, the gain variable limiter 201 may not be able to reduce the gain in time, and the output audio signal A1 may exceed 0 dBFS. Therefore, a non-linear limiter 202 is provided after the variable gain limiter 201. The non-linear limiter 202 limits the audio signal A1 exceeding 0 dBFS to 0 dBFS or less, and outputs the output audio signal OUT. However, the non-linear limiter 202 limits the amplitude by distorting the audio signal A1 exceeding -6 dBFS. Therefore, when the audio signal A1 exceeds 5 kHz, the output audio signal OUT of the non-linear limiter 202 has a problem that harmonics of the audio signal A1 are generated as aliasing noise. Therefore, a low-pass filter is provided in front of the non-linear limiter 202 and the band of the audio signal A1 is limited to suppress the generation of higher harmonics, or a low-pass filter is provided in the subsequent stage of the non-linear limiter 202 to suppress the occurrence of aliasing noise. A method is conceivable. However, in the case of the above method, since the low-pass filter is applied to the audio signal to be recorded, there is a problem that the band of the audio signal to be recorded is limited. Hereinafter, the configuration of the voice processing unit 103 for solving the above-described problem will be described.

  FIG. 5 is a block diagram illustrating a configuration example of the audio processing unit 103 according to the present embodiment. Hereinafter, the sound processing method (limiter process) of the sound processing unit 103 will be described. The audio processing unit 103 includes a gain variable limiter 201, a non-linear limiter 202, a low pass filter (LPF) 503, a delay unit 504, subtracters 505 and 506, and adders 507 and 508. The gain variable limiter 201 includes an amplification unit 203, a detection unit 204, and an amplification control unit 205, as in FIG. The audio processing unit 103 according to the present embodiment bypasses the non-linear limiter 202 for a signal in a band in which aliasing noise is generated by the non-linear limiter 202. The gain variable limiter 201 and the non-linear limiter 202 are the same as those in FIG.

  The low-pass filter 503 performs low-pass filtering processing (band limitation processing) on each of the plurality of output audio signals A1 from the amplification unit 203, and outputs a plurality of low-frequency band signals, respectively. For example, the low-pass filter 503 uses a finite impulse response filter (FIR filter) whose phase characteristics do not change depending on the frequency of the input signal. The low-pass filter 503 outputs a signal having a frequency lower than a predetermined frequency in the output audio signal A1 of the amplification unit 203. The delay unit 504 delays the plurality of output audio signals A1 from the amplification unit 203 by a delay time, and outputs the plurality of delayed signals. The delay time of the delay unit 504 is a delay time equivalent to the processing time of the low-pass filter 503. That is, the delay unit 504 is a timing adjustment unit for aligning the timings of the output signal of the delay unit 504 and the output signal of the low-pass filter 503.

  Subtractors 505 and 506 subtract a plurality of output signals (low frequency band signals) of low-pass filter 503 from a plurality of output signals of delay unit 504, respectively, and output a plurality of high frequency band signals to adders 507 and 508, respectively. To do. As in FIG. 2, the nonlinear limiter 202 multiplies a plurality of output signals (low frequency band signals) of the low-pass filter 503 by nonlinear coefficients, and outputs the plurality of signals to adders 507 and 508, respectively. For example, similar to the output audio signal OUT of FIG. 3, the non-linear limiter 202 determines that the low-pass filter 503 has an amplitude when the amplitude of the output signal of the low-pass filter 503 is greater than the second threshold (normalized value is 0.6). Multiply the output signal by the coefficient of the quadratic function. Adders 507 and 508 add the plurality of output signals (low frequency band signals) of the non-linear limiter 202 to the output signals (high frequency band signals) of the subtractors 505 and 506, respectively, and output the plurality of output audio signals OUT. Output each.

  As described above, in the nonlinear limiter 202, when the input signal exceeds 5 kHz, the harmonics of the input signal are generated as aliasing noise. Therefore, the low-pass filter 503 attenuates a frequency greater than 5 kHz in the output audio signal A1 of the amplification unit 203 and outputs a signal in a low frequency band of 5 kHz or less. Since the non-linear limiter 202 inputs a signal in a low frequency band of 5 kHz or less from the low-pass filter 503, no aliasing noise is generated and a signal without aliasing noise can be output. Since the subtracters 505 and 506 subtract the output signal (low frequency band signal of 5 kHz or less) of the low pass filter 503 from the output signal of the delay unit 504, the high frequency band signal higher than 5 kHz is output. The adders 507 and 508 add the output signals (high frequency band signals) of the subtracters 505 and 506 and the output signal (low frequency band signals) of the non-linear limiter 202, and output the output audio signal OUT. As a result, the output audio signal OUT becomes a high-quality audio signal without aliasing noise.

  The low-pass filter 503, the delay unit 504, and the subtractors 505 and 506 are division units, and divide the audio signal A1 into an audio signal in the first frequency band and an audio signal in the second frequency band. The low pass filter 503 outputs the audio signal in the first frequency band to the non-linear limiter 202. The subtracters 505 and 506 output the audio signal in the second frequency band to the adders 507 and 508. The second frequency band is a higher frequency band than the first frequency band. The first frequency band is a frequency band in which aliasing noise due to the non-linear limiter 202 does not occur, and the second frequency band is a frequency band in which aliasing noise due to the non-linear limiter 202 occurs. The non-linear limiter 202 is a first limiter that performs nonlinear limiter processing on an audio signal in the first frequency band. Adders 507 and 508 add the audio signal in the second frequency band and the output signal of nonlinear limiter 202.

(Second Embodiment)
FIG. 6 is a block diagram illustrating a configuration example of the audio processing unit 103 according to the second embodiment of the present invention. Hereinafter, a voice processing method (limiter process) of the voice processing unit 103 will be described. The voice processing unit 103 (FIG. 6) of the present embodiment is different from the voice processing unit 103 (FIG. 5) of the first embodiment in that a high pass filter (HPF) 604 is used instead of the delay unit 504 and the subtracters 505 and 506. Is provided. Hereinafter, the points of this embodiment different from the first embodiment will be described.

  The high-pass filter 604 performs high-pass filtering processing (band limitation processing) on each of the plurality of output audio signals A1 from the amplification unit 203, and outputs a plurality of high-frequency band signals. For example, the high pass filter 604 attenuates a frequency band of 5 kHz or less in the output audio signal A1 of the amplifying unit 203 and outputs a signal in a high frequency band higher than 5 kHz. The cut-off frequencies of the low-pass filter 503 and the high-pass filter 604 are both equivalent frequencies, for example, 5 kHz. For example, the high-pass filter 604 uses an FIR filter whose phase characteristics do not change depending on the frequency of the input signal. The adders 507 and 508 add the output signal (high frequency band signal) of the high pass filter 604 and the output signal (low frequency band signal) of the non-linear limiter 202, and output the output audio signal OUT. As a result, the output audio signal OUT becomes a high-quality audio signal without aliasing noise.

  The low-pass filter 503 and the high-pass filter 604 are division units, and divide the audio signal A1 into an audio signal in the first frequency band and an audio signal in the second frequency band. The low pass filter 503 outputs the audio signal in the first frequency band to the non-linear limiter 202. The high pass filter 604 outputs the audio signal in the second frequency band to the adders 507 and 508. The second frequency band is a higher frequency band than the first frequency band. The non-linear limiter 202 performs nonlinear limiter processing on the audio signal in the first frequency band. Adders 507 and 508 add the audio signal in the second frequency band and the output signal of nonlinear limiter 202.

  The above-described embodiments are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

201 Gain variable limiter, 202 Non-linear limiter, 203 Amplification unit, 204 Detection unit, 205 Amplification control unit, 503 Low pass filter, 504 Delay unit, 505, 506 Subtractor, 507, 508 Adder, 604 High pass filter

Claims (7)

Output means for inputting a first audio signal and outputting an audio signal in a first frequency band and an audio signal in a second frequency band higher than the first frequency band;
First limiter means for performing a limiter process on the audio signal of the first frequency band output from the output means;
Possess a sound signal of the second frequency band outputted from the output means, and adding means for adding the output signal from said first limiter means,
The output means includes
Low-pass filtering means for performing low-pass filtering on the first audio signal and outputting the audio signal in the first frequency band;
Speech processing apparatus characterized by chromatic and subtracting means for said first subtracts the audio signal of the first frequency band from the audio signal, and outputs the audio signal of the second frequency band.   2. The sound processing apparatus according to claim 1, wherein the first limiter means is non-linear limiter means for performing nonlinear limiter processing.   3. The audio according to claim 1, further comprising: a gain variable limiter that performs a limiter process on the second audio signal with a variable gain and outputs the first audio signal to the output unit. Processing equipment. The gain variable limiter means includes
Amplifying means for amplifying the second audio signal with a variable gain and outputting the first audio signal to the output means;
Detecting means for detecting a level of the second audio signal;
4. The audio processing apparatus according to claim 3, further comprising: an amplification control unit that controls a gain of the amplification unit according to a level detected by the detection unit. The output means includes delay means for outputting a signal obtained by delaying the first audio signal;
The subtracting means subtracts the audio signal of the first frequency band from the output signal of the delay means, and outputs the audio signal of the second frequency band . The speech processing apparatus according to item 1 . The first frequency band is a frequency band in which aliasing noise is not generated by the first limiter means,
It said second frequency band, the sound processing apparatus according to any one of claims 1 to 5, wherein the aliasing noise by the first limiter means is a frequency band generated. An output step of outputting an audio signal in a first frequency band and an audio signal in a second frequency band higher than the first frequency band by an output means to which the first audio signal is input;
A first limiter processing step for performing a limiter process on the audio signal of the first frequency band output from the output means by a first limiter;
The addition means, have a, an addition step for adding the audio signals the limit processing an audio signal of the outputted second frequency band from said output means,
The output step includes
A low-pass filter step of performing a low-pass filtering process on the first audio signal and outputting the audio signal of the first frequency band;
Audio processing method characterized by chromatic and subtraction steps of the first subtracting the audio signal of the first frequency band from the audio signal, and outputs the audio signal of the second frequency band.

Images