JP5036283B2 - Auto gain control device, audio signal recording device, video / audio signal recording device, and communication device - Google Patents

Description

  The present invention relates to an automatic gain control device, an audio recording device such as an IC recorder, a video / audio recording device such as a video camera, and a communication device such as a mobile phone.

  In an IC recorder, a video camera, and a mobile phone, since the position of the speaker and the volume of the voice vary, it is effective to automatically adjust the level of the signal received by the microphone to a certain level. Such processing is generally called auto gain control.

  FIG. 7 shows a conventional example of an auto gain control circuit (see Japanese Patent Application Laid-Open No. 8-297923).

  The signals L and R received by the left and right microphones are sent to the multiplication unit 1. The multiplier 1 multiplies each of the signals L and R by a gain control amount g1 given from the gain control amount calculation unit 3. The signals L and R whose gains have been adjusted by the multiplier 1 are sent to the A / D converters 2L and 2R, respectively, and converted into digital signals. The gain control amount calculation unit 3 calculates the gain control amount g1 based on the output signals of the A / D conversion units 2L and 2R, and gives the calculated gain control amount g1 to the multiplication unit 1.

  In the conventional auto gain control method, the input audio signal level is controlled according to a predetermined rule. However, the ideal method for correcting the input audio signal level differs depending on the acoustic environment.

  For example, when the target sound is conversation, it is preferable that gain control is instantly applied and a sound level that is always easy to hear is maintained. On the other hand, in the case of music at a performance, if a sound of an instrument for taking a rhythm such as a drum is included, a loud sound is generated periodically. In such an acoustic environment, if gain control is applied instantaneously in the same way as during conversation, vocal sounds other than drums will increase or decrease periodically, making the sound very uncomfortable. turn into. Therefore, when the sound source has a strong periodicity such as music, the adaptive speed of gain control should be slow.

Further, when wind noise is included in the input sound signal, by performing gain control, the level of the sound signal that is originally required changes according to the wind noise signal, and it becomes difficult to hear.
JP-A-8-297923 JP-A-5-7392 JP 2000-99069 A

  An object of the present invention is to provide an auto gain control device, an audio recording device, a video / audio recording device, and a communication device that enable auto gain control suitable for an acoustic environment.

The invention according to claim 1 is a determining means for determining an acoustic environment, a gain control amount determining means for determining a gain control amount based on a determination result by the determining means, and a gain control determined by the gain control amount determining means. Gain control means for performing gain control of the input acoustic signal based on the amount, the determination means determines the degree of periodicity of the input acoustic signal, and the gain control amount determination means includes: When the degree of periodicity of the input acoustic signal is high, the gain control amount is determined so that the response speed of gain control becomes slow .

According to a second aspect of the invention, in the audio signal recording apparatus, characterized in that it comprises an automatic gain control device of the mounting serial to claim 1.

According to a third aspect of the invention, the video and audio signal recording apparatus, characterized in that it comprises an automatic gain control device of the mounting serial to claim 1.

The invention described in claim 4 is the communication device, characterized in that it comprises an automatic gain control device of the mounting serial to claim 1.

  According to the present invention, it is possible to perform auto gain control suitable for an acoustic environment.

  Embodiments of the present invention applied to an audio signal processing circuit provided in a video camera will be described below with reference to the drawings. The acoustic environment refers to a part or all of a plurality of sound generation sources input to the apparatus.

  FIG. 1 shows the configuration of an audio signal processing circuit.

  The audio signal processing circuit includes a gain control unit 10, an acoustic environment determination unit 20, and a gain control amount determination unit 30.

  The gain control unit 10 includes a multiplication unit 11 and an A / D conversion unit 12. The acoustic environment determination unit 20 includes a gain correction unit 21 and an autocorrelation calculation unit 22.

An audio input signal from the microphone is sent to the multiplication unit 11 in the gain control unit 10. The multiplier 11 multiplies the audio input signal by the gain control amount g1 _t given by the gain control amount determination unit 30. The signal whose gain is adjusted by the multiplier 11 is sent to the A / D converter 12 and converted into a digital signal. The digital signal IN_H _t obtained by the A / D conversion unit 12 is output as an audio output signal and is sent to the acoustic environment determination unit 20 and the gain control amount determination unit 30.

The digital signal IN_H _t obtained by the A / D conversion unit 12 is input to the gain correction unit 21 in the acoustic environment determination unit 20. The gain control unit g1 _t calculated by the gain control amount determination unit 30 is also given to the gain correction unit 21. Gain correction unit 21 performs the calculation of IN_H _t / g1 _t, obtaining a signal IN _t before the gain control by the gain control section 10 is performed. The signal IN _t obtained by the gain correction unit 21 is sent to the autocorrelation calculation unit 22 in the acoustic environment determination unit 20.

Autocorrelation calculating unit 22, as shown in FIG. 2, on the basis of the signal IN _t sent from the gain correction unit 21, a predetermined number of samples consisting interval (evaluation value (512 * 1024 in this example) calculation interval D ) To calculate an autocorrelation evaluation value (total sum of autocorrelation of power values) for evaluating the autocorrelation of the voice band signal. The evaluation value calculation section D corresponds to about 12 seconds if the sampling frequency of the input signal is 44.1 kHz. When calculating the autocorrelation evaluation value for each evaluation value calculation section D, a sample in the section D and a predetermined number of samples (256 * 1024 in this example) immediately before the section D are used.

A method for calculating an autocorrelation evaluation value in an arbitrary evaluation value calculation section will be described. Each sample used to calculate an autocorrelation evaluation value in a certain evaluation value calculation section is expressed as IN _t (t = −M, − (M−1),..., −1, 0, 1, 2,. It will be expressed as IN ₀ represents the head sample of the evaluation value calculation section.

First, an autocorrelation evaluation value HS_AV _j (j = 0 to 255) is calculated based on the following equation (1).

The autocorrelation evaluation value HS_AV _j is a large value if the signal IN _t has periodicity. That is, if the voice has a rhythmic sense, the autocorrelation evaluation value HS_AV _j is a large value.

Next, the range of j> 10, the value HS_AV _j is maximized and HS_AVmax, when the HS_AV _j when it is j = 0 and HS_AV _0, the following equation (2), and calculates an autocorrelation value S . The _j> 10 HS_AV j in the range of was HS_AVmax a value that is a maximum in the range of j ≦ 10, there is a possibility that HS_AV _j increases even without periodicity.

S = HS_AVmax / HS_AV ₀ (2)

  S has a value close to 1.0 when the autocorrelation is strong.

  The autocorrelation value S calculated by the autocorrelation calculation unit 22 is given to the gain control amount determination unit 30.

Gain control amount determining unit 30, the autocorrelation value given from the autocorrelation calculating unit 22 S, A / D conversion section given from 12 signals IN_H _t, preset gain control target amplitude level Gtg, and preset based on the upper limit g_th _H and the lower limit value g_th _L of the gain control amount, by performing the calculation of the following equation (3), calculates a gain control amount gl _t.

T is a time constant that defines the response speed of the gain control control. The larger T is, the slower the response speed of the gain control control is. Further, IN_g _t is the weighted root mean square of the signal IN_H _t.

T = 10 * S + 1.0
_{IN_ g t = IN_ g t-} 1 × exp- (1 / T) + IN_ H t 2
g1 _t = Gtg * (1.5-S) / (IN _ g _t ) ^1/2
if g1 _t > g _TH _H * (1.5-S), then g1 _t = g _TH _H * (1.5-S)
if g1 _t <g _TH _L * (1.5-S), then g1 _t = g _TH _L * (1.5-S) (3)

  That is, when the autocorrelation value S of the input sound signal is large, it is determined that the input sound signal is a sound signal with strong periodicity, the time constant T is increased, and the response speed of the gain control control is decreased. Therefore, when the input sound is highly periodic music, or when the input sound is periodically mixed with loud or unnecessary sounds, the response speed of the gain control control can be slowed down. Therefore, it is possible to prevent the generation of a strange sound. In addition, since the gain control target amplitude level Gtg is multiplied by (1.5-S), the response speed becomes slow because the gain control target amplitude level is lowered for an audio signal with strong periodicity. The occurrence of an overrange of the signal level due to this can be suppressed.

  Conversely, when the autocorrelation value S of the input audio signal is small, the time constant T is reduced, and the response speed of gain control control is increased. Therefore, when a voice with low periodicity is input as in conversation or the like, the response speed of the gain control control can be increased, so that a voice level that is easy to hear is maintained by the gain control control. In addition, since the gain control target amplitude level Gtg is multiplied by (1.5-S), the gain control target amplitude level is increased for an audio signal having a low periodicity. It is possible to make effective use of the dynamic range of digital signals.

  FIG. 3 shows the configuration of the audio signal processing circuit.

  The audio signal processing circuit includes a gain control unit 110, an acoustic environment determination unit 120, and a gain control amount determination unit 130.

  The gain control unit 110 includes A / D conversion units 111L and 111R and a multiplication unit 112. The acoustic environment determination unit 120 includes a low-pass filter 121 and a wind noise mixture ratio determination unit 122. The gain control amount determination unit 130 includes an addition unit 131, a high-pass filter 132 with variable filter characteristics, a filter characteristic control unit 133, and a gain control amount calculation unit 134.

Audio input signals IN_L _t and IN_R _t from Lch and Rch microphones (not shown) are respectively sent to A / D converters 111L and 111R in the gain controller 110 and converted into digital signals. In this example, the sampling frequency of the A / D converters 111L and 111R is 48 kHz. The Lch and Rch digital signals output from the A / D converters 111L and 111R are sent to the multiplier 112. The multiplier 112 multiplies the Lch and Rch digital signals by the gain control amount g1 _t given by the gain control amount determination unit 130. The Lch and Rch signals IN_HL _t and IN_HR _t whose gains have been adjusted by the multiplier 112 are output as audio output signals OUT_L _t and OUT_R _t , and are also sent to the acoustic environment determination unit 120 and the gain control amount determination unit 130. .

The signals IN_HL _t and IN_HR _t input to the acoustic environment determination unit 120 are sent to the low-pass filter 121. Low-pass filter 121, the input signal IN_HL _t, against IN_HR _t, cut-off frequency by performing low-pass filtering 300 Hz, to obtain signal L_low _t, the R_low _t. The signals L_low _t and R_low _t that have passed through the low-pass filter 121 are sent to the wind noise mixture ratio determination unit 122.

First, the wind noise mixture ratio determination unit 122 calculates a correlation Wind_Lev _t between the signal L_low _t and the signal R_low _t based on the following equation (4).

Usually, in a video camera, since two microphones are arranged close to each other, the signal L_low _t and the signal R_low _t are substantially the same for a normal audio signal in a low frequency band. For this reason, Wind_Lev _t is almost zero. On the other hand, since wind noise is not a sound due to sound propagation, unlike signal L_low _t and signal R_low _t , Wind_Lev _t is close to 1.0 because the correlation is low.

That is, Wind_Lev _t is 0 when wind noise is not included, and Wind_Lev _t is 1.0 when all wind noise is present. Therefore, the wind noise mixing ratio is estimated by the above equation (4). Is possible.

Wind_Lev _t calculated by the wind noise mixture ratio determination unit 122 is sent to the filter characteristic control unit 133 in the gain control amount determination unit 130. On the other hand, the signals IN_HL _t and IN_HR _t input to the gain control amount determining unit 130 are added by the adding unit 131 and then sent to the high-pass filter 132.

The filter characteristic control unit 133 adaptively controls the characteristics of the high-pass filter 132 as shown in FIG. 4 according to Wind_Lev _t . That is, the characteristic of the high-pass filter 132 is changed so that the degree of reduction of the low frequency signal of 300 Hz or less increases as the mixing ratio of wind noise increases (wind_lev _t increases). As a result, the high-pass filter 132 reduces the low-frequency signal including wind noise from the signal (IN_HL _t + IN_HR _t ) obtained by the adder 131.

The signal IN_H2 _{t that} has passed through the high-pass filter 132 is sent to the gain control amount calculation unit 134. The gain control amount calculation unit 134 includes the signal IN_H2 _t that has passed through the high-pass filter 132, a preset time constant T, a preset gain control target amplitude level Gtg, and a preset gain control amount upper limit value g_TH. based on _H, by performing the calculation of the following expression (5), calculates a gain control amount gl _t. Incidentally, IN_g _t is the weighted root mean square of the signal IN_H2 _t.

_{IN_ g t = IN_ g t-} 1 × exp- (1 / T) + IN_ H2 t 2
_{g1 t = Gtg / (IN_ g} t) 1/2
if g1 _t > g _TH _H , then g1 _t = g _TH _H (5)

  In the above embodiment, since the gain control amount is calculated based on the audio signal from which the wind noise is adaptively removed according to the wind noise mixing ratio, the gain control amount changes due to sudden wind noise. Therefore, the target sound level can be suitably controlled.

  In the above-described first and second embodiments, the case where the present invention is applied to an audio signal processing circuit of a video camera has been described. It is possible to apply to a communication device such as. That is, the audio signal processing circuit according to the first and second embodiments is a voice signal processing circuit of a voice recording device such as an IC recorder provided with a microphone for voice input and a circuit for recording voice input from the microphone. Can be used as Also, the audio signal processing circuits described in the first and second embodiments are used as an audio signal processing circuit of a telephone device such as a portable telephone provided with a microphone for inputting voice and a circuit for transmitting voice input from the microphone. be able to.

  FIG. 5 shows the configuration of the audio signal processing circuit.

  The audio signal processing circuit includes a passband / gain control unit 210 and an acoustic environment determination unit 220.

The passband / gain control unit 210 includes an input signal processing unit 211 that performs filter processing or multiplication processing, a gain control amount calculation unit 212 that calculates a gain control amount gl _t based on the output signal IN_H _t of the input signal processing unit 211, and and a control unit 213 for controlling the input signal processing section 211 based on the determination signal and the gain control value gl _t from the acoustic environment determining unit 220. The input signal processing unit 211 includes a band filter with variable filter characteristics and a multiplication unit.

  A video signal (video input signal) taken by a video camera is input to the acoustic environment determination unit 220. The acoustic environment determination unit 220 determines whether or not a person mainly exists in the captured video based on the video input signal. If there is a person, it is determined whether or not there is a moving object that generates a loud sound such as an automobile in the background.

  The determination of whether or not a person is present is performed using, for example, face recognition technology. Whether or not there is a moving object is determined using, for example, a moving object detection technique.

  When the acoustic environment determination unit 220 detects both a person and a moving body, for example, the acoustic environment determination unit 220 outputs a first determination signal, and when at least one of the person and the moving body cannot be detected. The second determination signal is output. The determination signal output from the acoustic environment determination unit 220 is sent to the control unit 213 in the passband / gain control unit 210.

The audio input signal is input to the input signal processing unit 211 in the passband / gain control unit 210. The input signal processing unit 211 performs filter processing or multiplication processing described later. Output signal IN_H _t of the input signal processing unit 211 is output as an audio output signal, also sent to the gain control amount calculating section 212 of the pass-band gain control section 210.

The gain control amount calculation unit 212 outputs the output signal IN_H _t of the input signal processing unit 211, a preset time constant T, a preset gain control target amplitude level Gtg, and a preset gain control amount upper limit value g_TH _H. based on, by performing the calculation of the following expression (6), calculates a gain control amount gl _t. Incidentally, IN_g _t is the weighted root mean square of the signal IN_H _t.

_{IN_ g t = IN_ g t-} 1 × exp- (1 / T) + IN_ H t 2
_{g1 t = Gtg / (IN_ g} t) 1/2
if g1 _t > g _TH _H , then g1 _t = g _TH _H (6)

Gain control value gl _t calculated by the gain control amount calculator 212 is sent to the control unit 213. Control unit 213, based on the gain control value gl _t sent from the determination signal and the gain control amount calculating section 212 sent from the acoustic environment determining unit 220 performs the following control.

(1) When the determination signal is the first determination signal When the determination signal sent from the acoustic environment determination unit 220 is the first determination signal, the input signal processing unit 211 performs filtering processing. At this time, it controls based on the characteristics of the bandpass filter in the input signal processing unit 211 to the gain control amount gl _t. As the band filter in the input signal processing unit 211, a band filter whose characteristics are variable based on a band filter having cutoff frequencies of 100 Hz and 300 Hz is used.

(1-1) When gl _t = 1.0 When gl _t = 1.0, the characteristics of the band-pass filter are made flat as shown in FIG. Leave as it is.

(1-2) When gl _t > 1.0 When gl _t > 1.0, the cutoff frequency is set to 100 Hz and 300 Hz as shown in FIG. 6B. the characteristics of the bandpass filter having, and the amplitude of the passband and gl _t. That is, when the determination signal is the first determination signal, there is a high possibility that noise has occurred. Therefore, a signal of 100 Hz to 300 Hz, which is a band mainly including voice, is amplified, and a signal other than the voice band is not amplified. Like that.

(1-3) When gl _t <1.0 When gl _t <1.0, the cutoff frequency is set to 100 Hz and 300 Hz as shown in FIG. It is assumed that the band-pass filter has a characteristic, and the amplitude of the pass band is gl _t / 2. That is, when the determination signal is the first determination signal, there is a high possibility that noise has occurred. Therefore, the attenuation amount of the signal of 100 Hz to 300 Hz, which is a band mainly including sound, is reduced, and the signal other than the sound band Is greatly attenuated.

(2) When the determination signal is the second determination signal When the determination signal sent from the acoustic environment determination unit 220 is the second determination signal, the input signal processing unit 211 is given a gain control amount g1 _t . Then, a multiplication process using the gain control amount g1 _t as a multiplication coefficient is performed.

The input signal processing unit 211 performs the following processing based on control by the control unit 213. That is, when the determination signal from the acoustic environment determination unit 220 is the first determination signal, the input signal processing unit 211 inputs the input audio signal to the bandpass filter whose filter characteristics are controlled by the control unit 213, and inputs Amplify or attenuate audio signals. When the determination signal from the acoustic environment determination unit 220 is the second determination signal, the input signal processing unit 211 multiplies the input audio signal by the gain control amount g1 _t given from the control unit 213.

  By the way, when a person is photographed with a video camera, temporarily generated environmental noise prevents the recording of the sound produced by the person. Therefore, in this embodiment, it is determined whether both the person and the moving object are present in the photographed video based on the photographed video, and when both the person and the moving object are present in the photographed video. Makes it easy to hear the target sound by emphasizing the audio signal in the audio band and attenuating the audio signal in the other band.

It is a block diagram which shows the structure of the audio | voice signal processing circuit which is 1st Example. It is a schematic diagram which shows that the autocorrelation calculation part 22 calculates an autocorrelation evaluation value for every area D which consists of a predetermined number of samples. It is a block diagram which shows the structure of the audio | voice signal processing circuit which is 2nd Example. 5 is a graph showing an example of control of characteristics of a high-pass filter 132. It is a block diagram which shows the structure of the audio | voice signal processing circuit which is 3rd Example. 5 is a graph showing an example of control of characteristics of a band filter in an input signal processing unit 211. It is a block diagram which shows the prior art example of an auto gain control circuit.

Explanation of symbols

10, 110 Gain control unit 20, 120 Acoustic environment determination unit 30, 130 Gain control amount determination unit 11 Multiplication unit 12 A / D conversion unit 21 Gain correction unit 22 Autocorrelation calculation unit 111L, 111R A / D conversion unit 112 Multiplication Unit 121 low-pass filter 122 wind noise mixing ratio determination unit 131 addition unit 132 high-pass filter 133 filter characteristic control unit 134 gain control amount calculation unit

Claims (4)

A determination means for determining an acoustic environment;
Gain control amount determining means for determining a gain control amount based on a determination result by the determining means;
And gain control means for performing gain control of the input acoustic signal based on the gain control amount determined by the gain control amount determination means ,
The determination means determines the degree of periodicity of the input acoustic signal,
The gain control amount determination means determines the gain control amount so that the response speed of the gain control becomes slow when the degree of periodicity of the input acoustic signal is high. Control device. An acoustic signal recording apparatus comprising the auto gain control apparatus according to claim 1. A video / audio signal recording apparatus comprising the auto gain control apparatus according to claim 1. A call device comprising the auto gain control device according to claim 1.

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