JP2008129107A - Automatic gain control device, audio recording device, video/audio recording device and telephone call device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic gain control device capable of preventing that an audio signal level is fluctuated by wind noise, and also preventing that a signal after gain adjustment exceeds a range of an A/D converter by influence of the wind noise. <P>SOLUTION: The automatic gain control device comprises: an automatic gain control means for controlling a gain so that a whole frequency band signal level of an input audio signal may become a fixed level; a low sound removal means for removing a low frequency band signal from an output signal of the automatic gain control means; and an automatic gain correction means for controlling the gain so that an output signal level may become a fixed level, after gain control by the automatic gain control means is negated for the output signal of the low sound removal means. <P>COPYRIGHT: (C)2008,JPO&INPIT

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. 4 shows a first 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 gain control unit 101. The gain control unit 101 multiplies each of the signals L and R by the gain control amount g1 given from the gain control amount calculation unit 103. The signals L and R whose gains have been adjusted by the gain control unit 101 are sent to A / D converters 102L and 102R, respectively, and converted into digital signals. The gain control amount calculation unit 103 calculates the gain control amount g1 based on the output signals of the A / D converters 102L and 102R, and gives the calculated gain control amount g1 to the gain control unit 101.

  By the way, when an IC recorder, a video camera, or a mobile phone is used outdoors, a signal received by a microphone may contain wind noise. Wind noise is a sound having a large spectrum in a frequency band of 200 Hz or less, and is a sound generated by wind turbulence or a sound generated by directly applying pressure to a diaphragm of a microphone. Various methods have been proposed for determining and removing the presence of wind noise. When the correlation between Lch and Rch is low, it is determined that wind noise is included, and the most common method is to cut or reduce the low frequency component of the input speech with a high-pass filter or the like (Japanese Patent Laid-Open No. Hei 5-). 7392).

  In the first conventional example shown in FIG. 4, since the gain control amount is calculated based on the power of the input signal, the sound signal level fluctuates due to wind noise, and unnaturalness due to sound fluctuations is conspicuous. .

  FIG. 5 shows a second conventional example of an auto gain control circuit.

In the second conventional example, the gain control amount calculation unit 103 calculates the gain control amount g1 based on signals obtained by cutting the low-frequency components from the output signals of the A / D converters 102L and 102R by the high-pass filters 104L and 104R. ing. For this reason, the problem as in the first conventional example does not occur, but when a large bass such as wind noise is input, the signal after gain adjustment exceeds the range of the A / D converters 102L and 102R. There is a problem that the signal may be crushed. Once the signal is crushed due to the range over, a harmonic signal is generated. Therefore, it is impossible to remove the harmonic signal later.
JP-A-8-297923 JP-A-5-7392

  The present invention can prevent an audio signal level from fluctuating due to wind noise, and can prevent a signal after gain adjustment from exceeding the range of an A / D converter due to the influence of wind noise. An object is to provide an audio recording device, a video / audio recording device, and a communication device.

  According to the first aspect of the present invention, there is provided an auto gain control means for controlling so that the entire frequency band signal level of the input audio signal becomes a constant level, and a bass elimination for removing a low frequency band signal from the output signal of the auto gain control means. And an automatic gain correction means for controlling the output signal level to be a constant level after canceling the gain control by the automatic gain control means for the output signal of the bass removing means. .

  According to a second aspect of the present invention, in the auto gain control device according to the first aspect, the bass sound removing means is a high-pass filter for removing a signal in a low frequency band from the output signal of the auto gain control means. Extraction means for extracting a low frequency band signal from the output signal of the gain control means, estimation means for estimating a ratio of wind noise contained in the low frequency band signal based on the low frequency band signal extracted by the extraction means, and Filter characteristic control means for controlling the characteristics of the high-pass filter based on the ratio of wind noise estimated by the estimation means is provided, and the filter characteristic control means is a ratio of wind noise included in the voice input signal. The filter of the high-pass filter increases so that the degree of reduction of the low frequency band from the output signal of the auto gain control means increases as the Characterized in that it is intended to control the properties.

  According to a third aspect of the present invention, there is provided an auto gain control means for controlling the entire frequency band signal level of the input audio signal to be a constant level, and a signal for removing a low frequency band from the output signal of the auto gain control means. Extraction means for extracting a low frequency band signal from the output signal of the high pass filter, auto gain control means, the ratio of wind noise contained in the low frequency band signal based on the low frequency band signal extracted by the extraction means Based on the gain control amount in the estimation means to be estimated and the auto gain control means, the low-frequency band signal extracted by the extraction means, and the wind noise ratio estimated by the estimation means, Gain correction means is provided to perform gain correction on the output signal of the high-pass filter so that the signal level excluding noise is constant. It is characterized in.

  According to a fourth aspect of the present invention, in the auto gain control apparatus according to the second aspect of the present invention, the auto gain control device further comprises filter characteristic control means for controlling the characteristic of the high-pass filter based on the ratio of wind noise estimated by the estimation means. The filter characteristic control means is configured so that the degree of reduction of the low frequency band from the output signal of the auto gain control means increases as the ratio of wind noise included in the audio input signal increases. The filter characteristic is controlled.

  According to a fifth aspect of the present invention, an audio recording apparatus includes the auto gain control device according to the first to fourth aspects.

  According to a sixth aspect of the present invention, in the video / audio recording apparatus, the automatic gain control device according to the first to fourth aspects is provided.

  According to a seventh aspect of the present invention, in the communication device, the automatic gain control device according to the first to fourth aspects is provided.

  According to the present invention, it is possible to prevent the sound signal level from fluctuating due to wind noise, and to prevent the signal after gain adjustment from exceeding the range of the A / D converter due to the influence of wind noise. .

  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.

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

  The audio signal processing circuit includes an auto gain control unit 10, a bass removal unit 20, and an auto gain correction unit 30.

  The auto gain control unit 10 includes a gain control unit 11, A / D converters 12L and 12R, and a first gain control amount calculation unit 13. The bass removing unit 20 includes low-pass filters 21L and 21R, a wind noise mixture ratio prediction unit 22, and high-pass filters 23L and 23R. The auto gain correction unit 30 includes a gain correction unit 31 and a second gain control amount calculation unit 32.

[1] Description of Auto Gain Control Unit 10 Input signals L and R from Lch and Rch microphones (not shown) are sent to the gain control unit 11. Gain control section 11 is configured to multiply the first gain control amount G1_L _t for Lch provided by the first gain control amount calculating section 13 to the input signal L Lch, the relative input signal R of the Rch 1 multiplying the first gain control amount G1_R _t for Rch provided by the gain control amount calculating section 13. Signals Lch and Rch which is gain adjusted by the first gain control unit 11, respectively A / D converter 12L, sent to 12R, a digital signal IN_L _t, is converted into IN_R _t. The Lch and Rch digital signals IN_L _t and IN_R _t obtained by the A / D converters 12L and 12R are sent to the first gain control amount calculation unit 13 and also to the bass removal unit 20.

The first gain control amount calculation unit 13 uses the Lch and Rch digital signals IN_L _t and IN_R _t output from the A / D converters 12L and 12R to perform calculations as shown in the following equation (1). Accordingly, to calculate the first gain control amount G1_L _t and the first gain control amount G1_R _t for Rch for Lch.

IN_Lg _t = IN_Lg _t-1 × exp-(1 / T) + IN_L _t ²
IN_Rg _t = IN_Rg _t-1 xexp-(1 / T) + IN_R _t ²
_{g1_ L t = Gtg / (IN} _Lg t) 1/2
_{if g1 _ L t> g _TH} , then g1_ L t = g _THg
_{g1_ R t = Gtg / (IN} _Rg t) 1/2
_{if g1 _ R t> g _TH} , then g1_ R t = g _THg ... (1)

In the above formula _{(1), IN_Lg t, IN_Rg} t, T, Gtg, the meaning of g_TH is as follows.

IN_Lg _t: signal IN_L _t weighted mean square IN_Rg _t: signal IN_R _t weighted root mean T: a time constant (response time), the coefficient is set in advance Gtg: Lch, the gain control target amplitude level for Rch signal Yes, preset coefficient g_TH: upper limit of gain control amount for input audio signal, preset coefficient

The first gain control amounts g1_L _t and g1_R _t calculated by the first gain control amount calculation unit 13 are given to the gain control unit 11 and also to the second gain control amount calculation unit 32 in the auto gain correction unit 30. Given.

[2] Digital signal IN_L _t input to described bass removal unit 20 for the bass removal unit 20, IN_R _t are respectively a low-pass filter (LPF) 21L, together sent to 21R, feed a high-pass filter (HPF) 23L, the 23R It is done.

As the LPFs 21L and 21R, low-pass filters having a cutoff frequency of 300 Hz are used. The signals L_low _t and R_low _t that have passed through the LPFs 21L and 21R are sent to the wind noise mixture ratio prediction unit 22.

First, the wind noise mixture ratio prediction unit 22 calculates a correlation Wind_Lev _t between the signal L_low _t and the signal R_low _t based on the following equation (2).

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 (2). Is possible.

The wind noise mixing ratio prediction unit 22 adaptively controls the characteristics of both HPFs 23L and 23R as shown in FIG. 2 according to Wind_Lev _t calculated by the above equation (2). That is, the characteristics of both HPFs 23L and 23R are changed so that the degree of reduction of low frequency signals of 300 Hz or less increases as the mixing ratio of wind noise increases (wind_lev _t increases). Thereby, the low frequency signal containing wind noise is reduced from the input signal to the bass removing unit 20.

Each HPF23L, signals L_hi _t, R_hi _t which has passed through the 23R is sent to the automatic gain correction unit 30.

[3] auto gain correction unit 30 for description each HPF23L, signals passed through the 23R L_hi _t, R_hi _t is input to the gain correction unit 31. Gain correction unit 31, by multiplying the gain control amount G_L _t for Lch given to signal L_hi _t by the second gain control amount calculating section 32, and generates an output signal OUT_L _t of Lch, the signal R_hi _t by the gain control amount G_r _t for Rch provided by the second gain control amount calculating section 32, and generates an output signal OUT_R _t of Rch.

The signals OUT_L _t and OUT_R _{t that} have been gain-adjusted by the gain correction unit 31 are output as output signals and sent to the second gain control amount calculation unit 32.

The second gain control amount calculation unit 32 outputs the Lch and Rch first gain control amounts g1_L _t and g1_R _t calculated by the first gain control amount calculation unit 11 and the output signals OUT_L _t and OUT_R of the gain correction unit 31. with _t, and it performs the calculation of equation (3), calculates a gain control amount G_r _t of the gain control amount for G_L _t and Rch for Lch used in the gain correction unit 31.

OUT _Lg _t = OUT _LG _t-1 × exp- (1 / T) + OUT _L _t ²
OUT _Rg _t = OUT _RG _t-1 × exp- (1 / T) + OUT _R _t ²
_{g2_ L t = Gtg / (OUT_Lg} t) 1/2
_{g2_ R t = Gtg / (OUT_Rg} t) 1/2
_{G _ L t = g2_ L t} / g1 _ L t
_{if G_ L t> g _TH,} then G_ L t = g _TH
_{G _ R t = g2_ R t} / g1 _ R t
_{if G_ R t> g _TH,} then G_ R t = g _TH ... (3)

In the above formula _{(3), OUT_Lg t, OUT_Rg} t, T, g2_L t, g2_R t, Gtg, the meaning of g_TH is as follows.

For signals Lch the wind noise has been removed: OUT_Lg _t: signal OUT_L _t weighted mean square OUT_Rg _t: signal OUT_R _t weighted root mean T: a time constant (response time), the coefficient g2_L are preset _t Gain correction coefficient g2_R _t : Gain correction coefficient for Rch signal from which wind noise has been removed Gtg: Gain control target amplitude level, preset coefficient g_TH: Upper limit value of gain control amount, set in advance Coefficient

  That is, after canceling the gain control in the auto gain control unit 10, the auto gain correction unit 30 performs the auto gain control again on the signal in which the wind noise is adaptively reduced.

  In the above embodiment, the auto gain control unit 10 performs gain control based on a signal from which wind noise has not been removed. Therefore, the signal after gain adjustment is subjected to A / D conversion due to the influence of wind noise or loud bass. It becomes possible to prevent the range of the vessel from being exceeded. In addition, the auto gain correction unit 30 cancels the gain control in the auto gain control unit 10 and then performs auto gain control again on the signal in which the wind noise is adaptively reduced. It is possible to perform natural auto gain control that is adapted only to the audio signal necessary for the operation.

  FIG. 3 shows the configuration of the audio signal processing circuit. In FIG. 3, the same components as those in FIG.

The audio signal processing circuit includes an auto gain control unit 10, a bass removal unit 20, and an auto gain correction unit 40. The auto gain control unit 10 is the same as the auto gain control unit 10 of FIG. The bass removing unit 20 is the same as the bass removing unit 20 of FIG. However, LPF21L in bass removal unit 20, an output signal L_low _t of 21R, and R_low _t, Wind_Lev _t calculated by the wind noise mixing ratio prediction unit 22, the point that is being sent to the automatic gain correction unit 40 1 This is different from the bass removing unit 20. The auto gain correction unit 40 is different from the auto gain correction unit 30 of FIG.

  The auto gain correction unit 40 includes a gain correction unit 41 and a second gain control amount calculation unit 42.

The second gain control amount calculation unit 42 outputs the Lch and Rch first gain control amounts g1_L _t , g1_R _t , LPF 21L, 21R output signals L_low _t , R_low _t calculated by the first gain control amount calculation unit 13. And the Wind_Lev _t calculated by the wind noise mixture ratio prediction unit 22 is used to perform the calculation of the following equation (4), whereby the Lch gain control amount G_L _t and the Rch gain used in the gain correction unit 42 are calculated. to calculate the control amount G_R _t.

_{L _lowg 't = L _lowg'} t-1 × exp- (1 / T) + (Wind _ Lev t × L _ low t) 2
_{R _lowg 't = R _lowg'} t-1 × exp- (1 / T) + (Wind _ Lev t × R _ low t) 2
_{g3_ L t = Gtg / {(} Gtg / g1 _ L t) 2 -L _lowg 't} 1/2
_{g3_ R t = Gtg / {(} Gtg / g1 _ R t) 2 -R _lowg 't} 1/2
_{G _ L t = g3_ L t} / g1 _ L t
_{if G_ L t> g _TH,} then G_ L t = g _TH
_{G _ R t = g3_ R t} / g1 _ R t
_{if G_ R t> g _TH,} then G_ R t = g _TH ... (4)

In the above equation (4), L_lowg ′ _t , R_lowg ′ _t , T, g3_L _t , g3_R _t , Gtg, and g_TH have the following meanings.

L_lowg ' _t : Weighted mean square of wind noise contained in Lch low frequency signal R_lowg' _t : Weighted mean square of wind noise contained in Rch low frequency signal T: Time constant (response time), set in advance and has coefficients g3_L _t: gain correction coefficient for the signal of Lch the wind noise has been removed g3_R _t: gain for the signal Rch which wind noise has been removed correction coefficient g_th: the upper limit value of the gain control amount is set in advance Coefficient Gtg: Gain control target amplitude level, preset coefficient

Gain correction unit 41, by multiplying the gain control amount G_L _t for Lch provided by the second gain control amount calculating section 42 into a signal L_hi _t sent from the bass removal unit 20, Lch output signal OUT_L _t generates the, by the gain control amount G_r _t for Rch given to signal R_hi _t by the second gain control amount calculating section 42, and generates an output signal OUT_R _t of Rch.

The above formula (4) will be described. The gain control amount G_L _t and how the guidance of the gain control amount G_r _t for Rch are the same for Lch, illustrating only the gain control amount G_L _t for Lch.

An input audio signal IN_L _t, considered in isolation the wind noise component IN_L_win _t and other signals IN_L_S _t. The IN_L_Low _t the bass signal including wind noise, when actually the ratio of wind noise contained in the alpha and IN_L_Low _t, the input audio signal IN_L _t is separated into α · IN_L_Low _t and other signals IN_L_other _t can do. Therefore, the following equation (5) is established.

IN_L _t = IN_L_WIN _t + IN_L_S _t
= Α ・ IN_L_low _t + IN_L_other _t (5)

If a temporary range over in the A / D converter 12L is ignored, an ideal gain control amount g1_L_other _t is _expressed by the following equation (6).

IN_Lg_other _t = IN_Lg_other _t-1 xexp- (1 / T) + IN_L_other _t ²
g1_L_other _t = Gtg / (IN_Lg_other _t ) ^1/2 (6)

G1_L _t calculated by the first gain control amount calculation unit 13 is expressed by the following equation (7) from the above equation (1).

IN_Lg _t = IN_Lg _t-1 × exp-(1 / T) + IN_L _t ²
_{g1_ L t = Gtg / (IN} _Lg t) 1/2 ... (7)

IN_Lg _t is a weighted mean square of IN_L _t. Since IN_L _t = α · IN_L_Low _t + IN_L_other _t , IN_Lgt is _expressed by the following equation (8).

IN_Lg _t = IN_Lg _t-1 × exp- (1 / T) + IN_L _t ²
_{= IN_Lg t-1 × exp- (} 1 / T) + (α · IN_ L_ low t + IN_ L_ other t) 2
= IN_Lg _t-1 xexp- (1 / T)
+ (Α · IN_L_low _t ) ²
+2 {(α · IN_L_low _t ) × (IN_L_other _t )}
+ (IN_L_other _t ) ² (8)

IN_Lg_low ′ _t {weighted mean square of wind noise (α · IN_L_Low _t )}, IN_Lg_other _t, and IN_Lg_low & other _t are defined by the following equation (9).

IN_Lg_low ' _t = IN_Lg_low' _t-1 × exp- (1 / T) + (α ・ IN_L_low _t ) ²
IN_Lg_other _t = IN_Lg_other _t-1 xexp- (1 / T) + (IN_L_other _t ) ²
IN_Lg_low & other _t = IN_Lg_low & other _t-1 xexp- (1 / T)
+ (Α ・ IN_L_low _t ) × (IN_L_other _t )
... (9)

IN_Lg_low & other _t & other _t, when approximated to be zero by averaging, the equation (8) may approximated as shown in Equation (10).

_{IN _Lg t = IN_Lg_ low 't} + IN_Lg_ other t + 2 × IN _Lg_low & other t
≒ IN_Lg_ low ' _t + IN_Lg_ other _t (10)

First gain control amount G1_L _t is the formula (7) and from the formula (10) is expressed by the following equation (11).

_{g1_ L t = Gtg / (IN} _Lg t) 1/2
_{= Gtg / (IN_Lg_ low 't} + IN_Lg_ other t) 1/2 ... (11)

From Expression (11), IN_Lg_other _t is expressed by the following Expression (12).

IN_Lg_other _t = (Gtg / g1_L _t ) ² −IN_Lg_low ′ _t (12)

When Expression (12) is substituted into Expression (6), an ideal gain control amount g1_L_other _t is represented by the following Expression (13).

g1_L_other _t = Gtg / (IN_Lg_other _t ) ^1/2
= Gtg / {(Gtg / g1 _ L t) 2 - (IN_Lg_ low 't)} 1/2
... (13)

When α is replaced with Wind_Lev _t calculated by the wind noise mixture ratio prediction unit 22, IN_Lg_low ′ _t in the equation (13) is expressed as L_lowg ′ in the equation representing g3_L _t in the equation (4). _Since it is equal to _t , g3_L _t = g1_L_other _t , and g3_L _t is equal to the ideal gain control amount g1_L_other _t .

Second gain control amount calculating section 42, in order to counteract the effects of the gain control amount g1_ L _t of the auto gain control section 10, the gain control amount G_ L _t in the gain correction unit 41, (g3_ L _t / g1 are _ and L _t).

  In the first and second embodiments described above, the embodiments in the case where the present invention is applied to an audio signal processing circuit of a video camera have 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 includes a microphone for voice input and a voice signal processing circuit of a voice recording device such as an IC recorder provided with a circuit for recording voice input from the microphone. Can be used as Also, the audio signal processing circuit described in the first and second embodiments is used as an audio signal processing circuit of a communication device such as a portable telephone provided with a microphone for voice input and a circuit for transmitting voice input from the microphone. be able to.

It is a block diagram which shows the structure of the audio | voice signal processing circuit which is 1st Example. It is a graph which shows the example of control of the characteristic of the high pass filters 23L and 23R. It is a block diagram which shows the structure of the audio | voice signal processing circuit which is 2nd Example. It is a block diagram which shows the 1st prior art example of an auto gain control circuit. It is a block diagram which shows the 2nd prior art example of an auto gain control circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Auto gain control part 20 Bass removal part 30, 40 Auto gain correction part 11 Gain control part 12L, 12R A / D converter 13 1st gain control amount calculation part 21L, 21R Low pass filter 22 Wind noise mixing ratio prediction part 23L, 23R high-pass filter 31, 41 Gain correction unit 32, 42 Second gain control amount calculation unit

Claims (7)

Auto gain control means for controlling the signal level of the entire frequency band of the input audio signal to be a constant level;
The bass signal removing means for removing the low frequency band signal from the output signal of the auto gain control means, and the output signal level is set to a constant level after canceling the gain control by the auto gain control means for the output signal of the bass sound removing means. Auto gain correction means for controlling
An auto gain control device characterized by comprising: Bass removal means
A high-pass filter for removing signals in the low frequency band from the output signal of the auto gain control means,
Extraction means for extracting a low frequency band signal from the output signal of the auto gain control means;
An estimation means for estimating a ratio of wind noise included in the low frequency band signal based on the low frequency band signal extracted by the extraction means, and the high-pass filter based on the ratio of wind noise estimated by the estimation means Filter characteristic control means for controlling the characteristics of
The filter characteristic control means adjusts the filter characteristic of the high-pass filter so that the degree of reduction of the low frequency band from the output signal of the auto gain control means increases as the ratio of the wind noise contained in the audio input signal increases. The automatic gain control device according to claim 1, wherein the automatic gain control device is controlled. Auto gain control means for controlling the signal level of the entire frequency band of the input audio signal to be a constant level;
A high-pass filter for removing signals in the low frequency band from the output signal of the auto gain control means,
Extraction means for extracting a low frequency band signal from the output signal of the auto gain control means;
Based on the low frequency band signal extracted by the extraction means, the estimation means for estimating the ratio of wind noise included in the low frequency band signal, the gain control amount in the auto gain control means, and the low frequency extracted by the extraction means Based on the frequency band signal and the wind noise ratio estimated by the estimation means, the output signal of the high-pass filter is adjusted so that the level of the signal obtained by removing the wind noise from the input speech signal is constant. Gain correction means for performing gain correction;
An auto gain control device characterized by comprising: Filter characteristic control means for controlling the characteristics of the high-pass filter based on the ratio of wind noise estimated by the estimation means is provided, and the filter characteristic control means is a ratio of wind noise included in the voice input signal. The auto gain according to claim 3, wherein the filter characteristic of the high-pass filter is controlled so that the degree of reduction of the low frequency band from the output signal of the auto gain control means increases as the value of the auto gain control means increases. Control device. An audio recording device comprising the auto gain control device according to claim 1. A video / audio recording apparatus comprising the auto gain control apparatus according to claim 1. 5. A call device comprising the auto gain control device according to claim 1.

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