JPH05188972A - Noise reduction device - Google Patents

Abstract

(57) [Summary] [Purpose] Cancels noise components. With respect to the removal of noise components, a windshield is not used, which can contribute to downsizing of equipment and prevent deterioration of sound collection quality. Good sound collection quality can be achieved with a single processing system. While using a pair of omnidirectional microphones, it is possible to obtain stereophonic sound output. [Configuration] Noise component n of the outputs of the microphones 1 and 2
Is removed by the adaptive noise canceller 6, and the low-pass filter 11 extracts the omnidirectional audio signal component S in the low frequency range. The signal component output from the adder 22 can have a unidirectional characteristic, and the high pass filter 23 extracts a high frequency signal component. The adder 12 forms an audio signal output having omnidirectional characteristics in the low frequency range and unidirectional characteristics in the high frequency range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reducing device, and more particularly to a noise reducing device capable of reducing a noise component of a microphone output and obtaining a stereophonic voice output by using an omnidirectional microphone. ..

[0002]

2. Description of the Related Art Many microphones have a structure in which a change in sound pressure of sound waves is converted into mechanical vibration of a diaphragm and an electroacoustic conversion system is operated based on the vibration. Therefore, when the sound is picked up by the microphone, noise is generated if the diaphragm is affected by some factor.

If the above-mentioned factor is wind, noise due to wind [hereinafter, referred to as wind noise] is generated, and if the above-mentioned factor is vibration externally applied, noise due to vibration [hereinafter, referred to as noise due to vibration]. This is called vibration noise.

Examples of conventional techniques for reducing the above-mentioned wind noise are as follows. (1) Use of windscreen (windshield) (2) Use of electrical / acoustic high-pass filter (3) Adoption of configuration showing omnidirectionality in bass range

Further, as a conventional technique for reducing the above-mentioned vibration noise, there is, for example, the following one. (1) Adoption of anti-vibration mechanism (2) Adoption of omnidirectional microphone element (3) Analog noise cancellation method

[0006]

The conventional techniques for reducing the wind noise described above have the following problems, respectively. Against (1) ... Contrary to miniaturization of equipment. Generally, the larger the outer size of the windshield and the larger the distance between the microphone and the inner wall of the windshield, the smaller the wind noise.

With respect to (2) ... The sound collection quality deteriorates. Since the wind noise is mainly composed of low frequency components, it is effective to cut the low frequency components. However, in this case, not only the wind noise but also the low frequency components of the voice are cut.

In contrast to (3) ... The level at which wind noise is reduced is insufficient. Wind noise levels are lower in omnidirectional microphones than in directional microphones. However,
Actually, due to the influence of the housing around the microphone,
Just by adopting "a configuration showing omnidirectionality in the low range",
It will not be low enough.

Therefore, in the present situation where a device equipped with a microphone is further miniaturized and higher sound collecting quality is desired, wind noise can be further reduced only by the above-mentioned conventional technique. Is getting harder.
This applies to vibration noise as well.

By the way, conventionally, it has been impossible to obtain a stereoscopic sound output using only an omnidirectional microphone.

Therefore, a first object of the present invention is to provide a noise reduction device which can be miniaturized and can reliably remove noise. A second object of the present invention is to provide a noise reduction device that can obtain a stereophonic sound output by using an omnidirectional microphone.

[0012]

According to a first aspect of the present invention, a pair of microphones arranged close to each other so that a phase difference occurs between inputs, and one of the outputs of the pair of microphones. A means for forming a first difference signal by subtracting the output of the other microphone from the output, and the output of one of the microphones of the pair of microphones is used as a main input, and the first difference signal is referred to. Means for adaptively processing the main input and the reference input as the input,
A means for shifting the phase of the output of the other microphone among the outputs of the pair of microphones, and a means for subtracting the output of the means for shifting the phase from the output of the one microphone to form a second difference signal, From the output of the means for adaptively processing the first
And a means for separating the second signal component from the second difference signal and synthesizing the first and second signal components.

According to a second aspect of the present invention, two systems of the noise reducing device according to the first aspect are provided, one system is used as the output of the L channel microphone, and the other system is used as the output of the R channel microphone. It is configured.

[0014]

The operation of the noise reduction device according to claim 1 will be described. The outputs of the one and the other microphones include a voice signal component and a noise component. A first difference signal is formed by subtracting the output of one microphone from the output of the other microphone. This first difference signal has only a noise component, and the noise component is separated.

As a result, the output from one microphone contains a voice signal component and a noise component, and the output from the other microphone contains only a noise component. The output containing the above-mentioned voice signal component and noise component is the main input, and the output containing only the noise component is the reference input.

The reference input is adaptively processed to be equal to the noise component of the main input. By subtracting the adaptively processed reference input from the main input, only the noise component of the main input is minimized, that is, the voice signal component is maximized. Then, the first signal component, that is, the omnidirectional audio signal component in the low frequency band is separated from this audio signal.

The pair of microphones are constructed so that a phase difference is generated between the two inputs, and the output of the other microphone of the pair of microphones is phase-shifted.

By subtracting the output of the other phase-shifted microphone from the output [main input] of the one microphone, a directional second difference signal is formed. Then, from this second difference signal, a second signal component,
That is, the directional and middle-range and high-range signal components are separated.

The first and second signal components are combined into an output audio signal. As a result, the output obtained from the noise reduction device is unidirectional.

The operation of the noise reduction device according to claim 2 will be described. Two systems of the noise reduction device described in claim 1 are provided. Of the two systems, one system is used as the output of the L channel microphone, and the other system is used as the output of the R channel microphone. This makes it possible to obtain a stereophonic sound output.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the configuration of FIG. 1, the pair of microphones 1 and 2 arranged close to each other collects ambient sound, converts it into an electric signal, and outputs the electric signal. The microphones 1 and 2 are microphones of the same type, and
As shown in (1), since they are arranged close to each other, the same voice and noise are converted into an electric signal and output.

The arrangement of the microphones 1 and 2 is shown in FIG. The main axes of the microphones 1 and 2 are on the same straight line, and the sound receiving surfaces 1a of the microphones 1 and 2 are
2a are arranged facing each other with a distance d therebetween with a separator 20 in between.

When the microphones 1 and 2 are arranged in the state as shown in the figure, a predetermined phase difference occurs between the audio signals input to the microphones 1 and 2, and the microphones 1 and 2 have a low phase difference. It is known that among the outputs in the range, the voice signal components have almost the same phase, the wind noise components have substantially no correlation, and the vibration noise components have mutually opposite phases.

In FIG. 1, the electric signal output from the microphone 1 is supplied to the A / D conversion circuit 3, and the electric signal output from the microphone 2 is supplied to the A / D conversion circuit 4.

In the A / D conversion circuits 3 and 4, the electric signals supplied from the microphones 1 and 2 are converted into digital signals. The digital signal converted by the A / D conversion circuit 3 is the main input represented by (S + n). Also, A /
The digital signal converted by the D conversion circuit 4 is (S + (n
*)).

In the description of this embodiment, S represents a voice signal component, and n and (n *) represent a noise component composed of a vibration noise component and a wind noise component. The noise components n and (n *) have additivity, and the noise component (n *) has a correlation with the noise component n of the main input (S + n).

The above-mentioned main input (S + n) is the adder 5,
A delay circuit 7 provided in the adaptive noise canceller 6,
Further, it is supplied to the adder 22. Further, the output of the A / D conversion circuit 4 is supplied to the phase shift circuit 21, and the signal output from the A / D conversion circuit 4 and having a negative sign is supplied to the adder 5.

In the adder 5, a negative sign is added to A /
Output of D conversion circuit 4, that is, [-(S + (n *))]
Is added to the above-mentioned main input (S + n). As a result of this addition, the voice signal component S is removed and (n- (n *))
A reference input represented by is formed. The reference input (n
-(N *)) is supplied to the adaptive filter 9 of the adaptive noise canceller 6.

In the delay circuit 7 of the adaptive noise canceller 6, the main input (S + n) is delayed for a predetermined time and then output, and supplied to the adder 8. This delay is
It corresponds to the time delay required for the calculation for the adaptive processing or the time delay in the adaptive filter 9 and can be set appropriately according to the system configuration.

In the adder 8, the output from the delay circuit 7 and
The signal Y output from the adaptive filter 9 and having a negative sign is added. The signal Y is a component similar to the noise component n in the main input (S + n), as described later.

Therefore, in the adder 8, the main input (S +
The noise component n is subtracted from n) to maximize the voice signal component S. In other words, the noise component n of the main input (S + n) is minimized and virtually cancelled. The audio signal component S is fed back to the adaptive filter 9 and is also supplied to the low-pass filter 11.

The low-pass filter 11 extracts a low-frequency and omnidirectional voice signal component S from the output of the adaptive noise canceller 6 and supplies it to the adder 12.

On the other hand, in the phase shift circuit 21, in order to make the characteristic of the circuit block 26 having the configuration shown in FIG. 1 a unidirectional characteristic, specifically, a cardioid shape characteristic, the A / D conversion circuit 4 A predetermined amount of phase shift is applied to the output of.

FIG. 4 shows an example of the case where the phase shift circuit 21 is configured in an analog manner. This phase shift circuit 21
Is a low-pass filter including a resistor Ro and a capacitor Co. In this low pass filter, the resistance Ro
Is large, omnidirectional characteristics are exhibited, and when the resistance Ro is small, bidirectional characteristics, that is, a so-called "8-shaped" characteristic is exhibited. With this low-pass filter, the A / D conversion circuit 4
A predetermined amount of phase θ2 is given to the output from. The phase-shifted signal is supplied to the adder 22.

In the adder 22, the main input (S + n),
A signal [-(S + (n
*))] Is added. As described above, the microphones 1 and 2 are arranged so that a predetermined phase difference θ1 is generated at the time of input, and in the phase shift circuit 15, the above-mentioned signal [-
(S + (n *))] is given a predetermined amount of phase θ2.

Therefore, the phase of the signal output from the adder 22 is within the range of [θ2 ± θ1]. The phase difference [± θ1] exists in the output between the microphones 1 and 2
This is due to the relative position of the sound source with respect to the microphones 1 and 2.

Then, for example, when θ2 = θ1,
[Θ2 + θ1 = 2 × θ2], and [θ2-θ1 = 0]
Becomes On the characteristic diagram, although not shown, the above [θ2 +
θ1 = 0] corresponds to the rear end portion of the cardioid, that is, the 0 ° direction on the characteristic diagram. Then, the level also changes in accordance with the value of [θ2 ± θ1] described above, whereby a unidirectional characteristic is obtained. The output of the adder 22 is supplied to the high pass filter 17.

The high-pass filter 17 separates the high frequency signal component from the output of the adder 22. Then, the high frequency signal component is supplied to the adder 12.

The adder 12 adds the high-frequency signal component supplied from the high-pass filter 17 to the low-frequency audio signal component S supplied from the low-pass filter 11. As a result, the audio signal component S over the entire predetermined band from the low band to the high band is synthesized. As a result, omnidirectional signal components in the low frequency range and unidirectional signal components in the middle and high frequency ranges can be obtained. The signal component is supplied to the D / A conversion circuit 13.

The D / A conversion circuit 13 converts the audio signal component S represented by a digital signal into an analog signal, and the analog signal is taken out from the terminal 14.

The operation of the adaptive filter 9 of the adaptive noise canceller 6 will be described below. In the adaptive filter 9,
A signal Y is formed as a component similar to the noise component n of the main input (S + n). That is, the adaptive noise canceller 6
The filter characteristics are sequentially self-adjusted so that the output of ∘ is similar to the audio signal component S of the main input (S + n).

As the adaptive filter 9, an FIR filter type adaptive linear combiner having the configuration shown in FIG. 2 is used. In the configuration of FIG. 2, DL1 to DLL represent delay circuits, and MP0 to MPL represent coefficient multipliers. Further, 16 is an adder, and 15 and 17 are terminals, respectively.

[Z ^-1 ] in the above delay circuits DL1 to DLL represents the delay of the unit sampling time, and W _nk supplied to the coefficient multipliers MP0 to MPL represents the weighting coefficient. Normal FIR if the weighting factor W _nk is fixed
It is a digital filter.

Here, an algorithm for adaptively operating the adaptive filter 9 will be described. Various algorithms can be used as the calculation algorithm in the adaptive filter 9, but a practical and frequently used LMS (least mean square) algorithm, which requires a relatively small amount of calculation, will be described below.

If the input vector Xk is expressed as X _k = [X _k X _k-1 X _k-2 ... X _kL ], the output Y _k of the adaptive filter 9 is Given in.

Assuming that the output of the delay circuit 7 is d _k , the differential output [residual output] ε _k is ε _k = d ^T _KO −X _k W _k . In the above equation, "d ^T _KO " represents the high frequency signal of "d _k ". In the LMS (least mean square) method, the weight vector is updated according to the following formula. W _{k + 1} = W _k +2 με _k X _{k In the} above formula, μ is a gain factor that determines the speed and stability of adaptation, a so-called step gain.

By updating the weighting vector as described above, an action is taken to minimize the output power of the system. Hereinafter, this operation will be described by formulating. For simplicity, when the delay circuit 7 is ignored, the differential output ε from the adder 8 is ε = S + n−Y.

The expected value of the square of (ε) is expressed by the following equation. E [ε ² ] = E [S ² ] + E [(n−Y) ² ] + 2E
[S (n−Y)] Here, since S has no correlation with n and Y, in the above equation, E [S (n−Y)] = 0. Therefore, the expected value E [ε ² ] of the square of (ε) is expressed by the following equation. E [ε ² ] = E [S ² ] + E [(n−Y) ² ]

The adaptive filter 9 is adjusted so that E [ε ² ] is minimized, but since E [S ² ] is not affected, the following equation is obtained. Emin [ε ² ] = E [S ² ] + Emin [(n−Y) ² ]

Since E [S ² ] is not affected, E
Minimizing [ε ² ] means minimizing E [(n−Y) ² ]. Therefore, the output Y of the adaptive filter 9 is the best least squares estimation value of [n].

When E [(n−Y) ² ] is minimized,
Since [ε-S = n−Y], E [(ε−
S) ² ] is also minimized. Therefore, adjusting the adaptive filter 9 to minimize the total output power is equivalent to the difference output ε being the best least-squares estimated value of the voice signal component S.

The difference output ε is generally the voice signal component S with some noise component added, but the noise component to be output is given by (n−Y), so E [(n−Y) )
² ] is equivalent to maximizing the output signal-to-noise ratio.

In this embodiment, the circuit block 26 having the configuration shown in FIG. 1 is provided in two systems as shown in FIG. 5, so that even the omnidirectional microphones 1 and 2 can output a stereo sound. You are able to get it.

In FIG. 5, since each of the L and R channel circuit blocks 26 and 27 has a unidirectional characteristic,
By taking out the audio output from the circuit blocks 26 and 27 of the L and R channels from the terminals 14e and 14f, it is possible to give the audio output a stereo feeling.

The connection states of the circuit blocks 26 and 27 and the microphones 1 and 2 are not limited to the illustrated example. For example, as shown in FIG. 6, the microphones 1 and 2 may be commonly used, and the outputs of the microphones 1 and 2 may be supplied to the circuit blocks 26 and 27, respectively.

In this case, the channels connected to the microphones 1 and 2 are opposite to each other in the circuit blocks 26 and 27. That is, in the L-channel circuit block 26, the microphones 1 and 2 and the A / D conversion circuits 3 and 4 are shown in FIG.
In the R channel circuit block 27, the microphone 1 and the A / D conversion circuit 4 are connected, and the microphone 2 and the A / D conversion circuit 3 are connected.

In FIG. 5 and FIG. 6, for the low frequency band, for example, the output of the L channel circuit block 26 can be used.

FIG. 7 shows a first modification of the embodiment. This first modified example is different from the above-described one embodiment in that an adder 41 is arranged between the input side of the A / D conversion circuit 3 and the adaptive noise canceller 6, and the A / D conversion is performed.
That is, the adder 42 is arranged between the conversion circuit 4 and the input side of the adaptive noise canceller 6.

In this case, in the adder 41, both digital signals supplied from the A / D conversion circuits 3 and 4 are given a plus sign. However, in the adder 42, the digital signal supplied from the A / D conversion circuit 3 is given a positive sign, and the digital signal supplied from the A / D conversion circuit 4 is given a negative sign. There is.

Therefore, at the output of the adder 41, the voice signal component S doubled in level and the noise component (n + (n
*)) Is included and these added values, that is, [2S
+ (N + (n *))] is the main input. The main input [2S + (n + (n *))] is taken out from the terminal 43.

The output of the adder 42 is removed because the voice signal component S has the same phase, and the noise component (n- (n
*)) Only, and the noise component (n- (n *)) is used as a reference input. The reference input (n- (n *)) is the terminal 44.
Taken from. Further, among the noise components, the vibration noise components have opposite phases to each other and are therefore canceled, and as a result, almost only the wind noise components are included. This makes it possible to further enhance the noise reduction effect.

When this first modification is used, A /
The output extracted from the point PA on the output side of the D conversion circuit 3 is supplied to the adder 22 shown in the embodiment, and the output extracted from the point PB on the output side of the A / D conversion circuit 4. Is supplied to the phase shift circuit 21 shown in one embodiment. The contents of other configurations, actions, effects, etc. are the same as those in the above-mentioned one embodiment.
The same parts as those in the first embodiment are designated by the same reference numerals, and overlapping description will be omitted.

FIG. 8 shows a second modification of the embodiment. This second modified example is different from the above-described first embodiment in that only the processing of the adaptive noise canceller 6 is performed with a digital signal, and other signal processing is performed with an analog signal. Therefore, the adders 5, 12, 22 shown in the embodiment are changed to analog adders 36, 39, 37, and the phase shift circuit 21 is changed to the analog phase shift circuit 3.
It has been changed to 5.

Further, by providing analog low-pass filters 31 and 32 on the output sides of the microphones 1 and 2, respectively, only low-frequency signal components are supplied to subsequent circuit blocks. Then, the above-mentioned low-pass filter 31,
Both the input and output signal components of 32 are extracted and adders 33, 3
That is, the high-frequency signal component is extracted by calculating the difference in 4, and the high-frequency signal component is supplied to the adder 37, the phase shift circuit 35, and the like. In addition, other configurations, actions,
The contents of the effects and the like are the same as those in the above-described first embodiment, and therefore, the portions common to the first embodiment are denoted by the same reference numerals, and the duplicated description will be omitted.

According to this embodiment, the microphone 1,
Since the two main axes are on the same straight line and the sound receiving surfaces 1a and 2a are arranged facing each other with the distance d interposed therebetween, a phase difference occurs between the input audio signals. Main input (S + n) at adaptive noise canceller 6
From which the noise component n is subtracted and the voice signal component S is maximized. In other words, the noise component n of the main input (S + n) is minimized and substantially canceled, and the audio signal component S
Only the low frequency and omnidirectional audio signal component S is extracted by the low pass filter 11.

The main input (S + n) and the phase shift circuit 2
The output of the microphone 2 that is phase-shifted by 1 [-(S +
(N *))] is added by the adder 22 so that the signal component output from the adder 22 can have a directional characteristic, in this case, a unidirectional characteristic. From the output of the adder 22 having this unidirectional characteristic, a high-pass filter 23 extracts a high-frequency signal component.

In the adder 12, the low frequency audio signal component S and the high frequency signal component are added. As a result, an audio signal output having an omnidirectional characteristic in the low frequency range and a unidirectional characteristic in the high frequency range is formed.

Therefore, the normal pair of microphones 1, 2
By using, the noise component can be canceled. Regarding the removal of this noise component, the windshield is not used, and since the microphones 1 and 2 are arranged close to each other, it is possible to contribute to the miniaturization of the device, and it is necessary to use an electrical / acoustic high-pass filter or the like. Since there is no noise, it is possible to prevent the sound quality from being degraded.

Further, the vibration noise component can be removed by using the pair of normal microphones 1 and 2. The circuit block having the configuration shown in FIG. 1 has two channels, that is, L and R channel circuit blocks 26 and 2.
7. By providing, omnidirectional microphone 1,
While using 2, it is possible to obtain a voice output with a stereo feeling.

Since the adaptive noise canceller 6 is used, the characteristic of the adaptive filter 9 is automatically updated even if the characteristic of wind noise and / or vibration noise [for example, level or spectral distribution] changes. The wind noise component can be stably reduced.

Further, good sound collection quality can be realized by a single processing system without preparing a processing system for each type of noise.

According to the second modification of this embodiment, the output from the microphone 1 through the A / D conversion circuit 3 is supplied to the adders 41 and 42, and the microphone 2 performs A / D conversion. The output formed via the circuit 4 is supplied to the adder 41, and the signal formed by adding a negative sign to the output of the A / D conversion circuit 4 is supplied to the adder 43. Therefore,
In addition to the effect similar to that of the above-described embodiment, the sound signal component S
Can be doubled as compared with the above-mentioned embodiment.

The noise reduction device shown in this embodiment can be applied to a sound collecting system in various fields. For example, it can be applied to a small portable video camera device or a single microphone. The pair of microphones 1 and 2 shown in this embodiment can be used with or without directivity.

[0074]

According to the invention of claim 1, there is an effect that a noise component can be canceled. Regarding removal of noise components, a windshield is not used and a pair of microphones are placed close to each other, which contributes to downsizing of the device, and there is no need to use an electrical / acoustic high-pass filter or the like. There is an effect that it is possible to prevent deterioration of the sound collection quality. Further, there is an effect that good sound collection quality can be realized by a single processing system without preparing a processing system for each type of noise.

Further, according to the embodiment, since the adaptive noise canceller is used, the characteristic of noise [wind noise component + vibration noise component] [eg level or spectrum distribution]
Even if is changed, the characteristics of the adaptive filter are automatically updated, and the wind noise component can be stably reduced.

According to the invention of claim 2, in addition to the effect of claim 1, there is an effect that it is possible to obtain a stereo sound output while using a pair of omnidirectional microphones.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an adaptive filter.

FIG. 3 is a diagram showing an example of arrangement of a pair of microphones.

FIG. 4 is a circuit diagram showing an example of an analog phase shift circuit.

FIG. 5 is a block diagram showing a configuration for obtaining a stereo output.

FIG. 6 is a block diagram showing a configuration in which the outputs of a pair of microphones are used in the L and R channel circuit blocks when obtaining a stereo output.

FIG. 7 is a block diagram showing a first modification example of the embodiment.

FIG. 8 is a block diagram showing a second modification of the embodiment.

[Explanation of symbols]

 1, 2 Microphones 1a, 2a Sound receiving surface 5, 12, 22, 36, 37, 41, 42 Adder 6 Adaptive noise canceller 11 Low pass filter 20 Separator 21 Phase shift circuit 23 High pass filter 26 L channel circuit block 27 R channel Circuit block d distance

Claims (2)

[Claims] 1. A pair of microphones arranged close to each other so that a phase difference occurs between inputs, and an output of one of the outputs of the pair of microphones is subtracted from an output of the other microphone. A means for forming a first difference signal, and an output of one of the pair of microphones as a main input, and the first difference signal as a reference input, and the main input and the reference input A means for adaptively processing, a means for shifting the phase of the output of the other microphone of the outputs of the pair of microphones, and a subtraction of the output of the means for phase shifting from the output of the one microphone. , Separating the first signal component from the output of the means for forming the second difference signal and the means for adaptively processing, and separating the second signal component from the second difference signal, Noise reduction apparatus characterized by comprising a means for combining the first and second signal components. 2. A noise reduction device comprising two systems of the noise reduction device according to claim 1, one system being an output of an L channel microphone and the other system being an output of an R channel microphone. apparatus.