JP2003009278A - Microphone system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microphone system especially with directivity that is miniaturized more than a conventional microphone system so as to ensure sharp directivity. SOLUTION: The microphone system delays a main sound signal SM obtained from a main microphone 2 by a prescribed time, generates a subtraction signal between the delayed main sound signal and a sub sound signal SS obtained from a sub microphone 3 and applies adaptive processing to the main sound signal by using the subtraction signal as a reference input.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microphone device, and is particularly applicable to a microphone device having directivity. The present invention delays the main audio signal obtained from the main microphone by a predetermined time, and then generates a subtraction signal with the sub audio signal obtained from the sub microphone, and uses this subtraction signal as a reference input. By adaptively processing the main audio signal, it is possible to make the shape smaller and secure a sharp directivity as compared with the conventional one.

[0002]

2. Description of the Related Art Conventionally, in a super-directional microphone represented by a so-called gun microphone, an extremely sharp directivity is ensured by effectively utilizing the phase difference of sound waves propagating in the air.

That is, in this type of microphone, a microphone unit for converting air vibration into an electric signal is arranged at one end of a cylindrical member, and a sound wave obtained from a sound source is transmitted to the microphone unit through an opening at the other end of the cylindrical member. Lead. Openings are formed at predetermined intervals on the side surface of the tubular member, and the intervals of the openings are set so as to emphasize the amplitude of sound waves coming from a predetermined direction. As a result, in this type of microphone, the sound waves coming from the predetermined direction are emphasized in amplitude and converted into a sound signal by the microphone unit, and the sound waves coming from other directions are suppressed in amplitude and converted into a sound signal. However, an extremely sharp directivity is ensured.

[0004]

However, according to such a principle of operation, in the conventional superdirective microphone, if the directivity is sharpened, the length of the tubular member must be lengthened accordingly. After all, there is a problem that the entire shape becomes large.

If such a sharp directivity can be ensured by a compact shape, it is considered convenient because portability is improved accordingly.

The present invention has been made in consideration of the above points, and an object thereof is to propose a microphone device having a sharp directivity which can be downsized in comparison with the conventional one.

[0007]

In order to solve such a problem, in the invention of claim 1, the main microphone for outputting the main audio signal and the main microphone are arranged apart from each other by a predetermined distance. A sub microphone that outputs a sub audio signal, a delay circuit that delays and outputs the main audio signal for a predetermined delay time, and an output signal of the delay circuit and a subtraction signal of the main audio signal. A subtraction circuit,
A filter circuit for flattening the frequency characteristic of the subtracted signal and an adaptive processing circuit for adaptively processing the main audio signal using the output signal of the filter circuit are provided.

According to the first aspect of the invention, the main microphone that outputs the main audio signal and the sub microphone that outputs the sub audio signal are separated by a predetermined distance. The main and sub audio signals have a phase difference according to this predetermined distance and the arrival direction of the sound wave. Also, by providing a delay circuit that delays and outputs the main audio signal for a predetermined delay time and a subtraction circuit that outputs a subtraction signal of the output signal of the delay circuit and the main audio signal, According to the delay time of the delay circuit, the sound waves arriving from the predetermined direction can have the same phase between the input signals of the subtraction circuit. Accordingly, if a filter circuit for flattening the frequency characteristic of the subtraction signal and an adaptive processing circuit for adaptively processing the main audio signal by using the output signal of the filter circuit are provided, between the input signals of the subtraction circuit. Then, the main voice signal is adaptively processed by the signal component that becomes the noise component with respect to the signal component that has the same phase, so that the sharp directivity can be secured due to the small size.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings as appropriate.

(1) First Embodiment (1-1) Configuration of the First Embodiment FIG. 1 is a block diagram showing a microphone device according to the first embodiment of the present invention. This microphone device 1
In, the main microphone 2 and the sub microphone 3
Is an omnidirectional microphone having substantially the same sensitivity characteristics, which are arranged in a straight line at a predetermined distance d and convert air vibrations into electrical signals to obtain main and sub audio signals SM and SS, respectively. Is output.

The amplifier circuits 4 and 5 are set so as to have substantially the same frequency characteristics, and the main and sub audio signals SM and SS output from the main microphone 2 and the sub microphone 3 respectively with almost the same gain. Is amplified and output.

Analog-to-digital conversion circuit (A / D) 6
And 7 are configured identically, and amplifying circuits 4 and 5 respectively
The analog-to-digital conversion processing is performed on the output signal of 1 to output the main and sub audio data.

The delay circuits (τ) 8A to 8N are connected in series and delay the main audio data input to one end by a predetermined time and output the delayed main audio data. Here, in this embodiment, after the sound wave S coming from the main microphone 2 side reaches the main microphone 2 on a straight line formed by arranging the main microphone 2 and the sub microphone 3, the sub microphone The time T until reaching 2 is these delay circuits 8A
The delay time is set to 8N. That is, such a time T is represented by T = d / c, where the speed of sound is c, while the delay circuit 8A
The delay time of the series circuit of 8N is 8A to 8N.
Assuming that the number of N is n and each delay time is τ, nτ
It is represented by. As a result, in this embodiment, the number n of the delay circuits 8A to 8N is set to d / cτ.

When set in this way, the delay circuit 8A
The main audio data output from the series circuit of 8N and the sub audio data output from the analog-digital conversion circuit 7 are mainly on a straight line formed by arranging the main microphone 2 and the sub microphone 3. The sound wave S arriving from the microphone 2 side has the same phase. On the other hand, a sound wave (which becomes noise in this embodiment) N coming from directions other than this direction has a phase difference according to the direction of arrival and the wavelength.

The subtraction circuit 9 subtracts the sub audio data from the main audio data to remove the in-phase component from the main and sub audio data and outputs the result. As a result, the subtraction circuit 9 extracts audio data (hereinafter referred to as noise data) that is a noise component for the sound wave S coming from the main microphone 2 side on the straight line formed by arranging the microphones 2 and 3. Output.

The amplifier circuit 10 amplifies this noise data with a predetermined gain and outputs it, and a low-pass filter (LPF) 11
Outputs the frequency characteristics of the noise data output from the amplifier circuit 10 with the frequency characteristics of −6 [dB / oct] being flattened.

The adaptive processing circuit 12 receives the noise data output from the low-pass filter 11 as a reference input, and uses the noise data to adaptively process the main voice data output from the delay circuits 8A to 8N. Due to
The noise component contained in the main voice data is removed.

Here, in the adaptive processing circuit 12, the adaptive filter 13 has a least mean square (LMS: Least Mean).
Square (Fourier) algorithm is used to switch the tap coefficient in accordance with the output data of the adaptive processing circuit 12.
nite Impulse Response) filter, and corrects and outputs the output data of the low-pass filter 11.

The delay circuit 14 has delay circuits 8A to 8N so as to correspond to the delay time in the adaptive filter 13.
The main audio data output from is delayed and output.
The subtraction circuit 15 subtracts the output data of the adaptive filter 13 from the output data of the delay circuit 14, thereby outputting sound data having a strong directivity with respect to the sound wave S coming from the direction of the microphone 2 toward the microphone 3. To do. A digital-analog conversion circuit (D / A) 16 performs digital-analog conversion processing on this voice data and outputs a voice signal from this microphone device 1.

(1-2) Operation of the First Embodiment In the above-described configuration, in the microphone device 1, the main and sub microphones 2 and 3 are arranged with a predetermined distance d between them. With respect to the arrangement direction of the sub microphones 2 and 3, and the sound wave S arriving from the main microphone 2 side, in the main and sub audio signals SS and SM obtained from the microphones 2 and 3, the sound wave S has the distance d The phase difference becomes equal to the time required for propagation. On the other hand, in the sound wave N arriving from other than this direction, the main and sub audio signals SS and SM are obtained by the phase difference according to the distance d and the arrival direction.

In the microphone device 1, the delay circuit 8A corresponds to the time required for the sound wave S to propagate through the distance d.
8N delays audio data obtained by analog-to-digital conversion processing of the main audio signal SS, whereby the main audio data has an arrangement direction of the microphones 2 and 3 with respect to the corresponding auxiliary audio data. The sound wave S arriving from the microphone 2 side has the same phase, while the sound wave N arriving from a direction other than this direction is
It will have a phase difference.

In the microphone device 1, subtraction data is generated in the subtraction circuit 9 between the main and sub audio data, whereby the arrangement directions of the microphones 2 and 3 are
A signal component, which is a noise component, is extracted from the sound wave S coming from the main microphone 2 side. Further, in the adaptive processing circuit 12, the main voice data is adaptively processed by using the signal component which becomes the noise component as a reference input, whereby components having a high correlation with the noise component are removed from the main voice data, and by these, the microphone. The device 1 has a sufficient sensitivity to the arrangement direction of the microphones 2 and 3 and the sound wave S coming from the main microphone 2 side, and sufficiently suppresses the sensitivity to sound waves coming from other directions. Can be secured. As a result, in this microphone device 1, the two microphones 2 and 3 are
It is possible to electrically process the output signal of 1 to secure sharp directivity, and to miniaturize the overall shape to secure superdirectivity.

(1-3) Effects of the First Embodiment According to the above configuration, the main audio signal obtained from the main microphone is delayed by a predetermined time, and then the sub audio obtained from the sub microphone. By generating a subtraction signal from the audio signal and adaptively processing the main audio signal using the subtraction signal as a reference input, it is possible to reduce the shape and secure sharp directivity as compared with the conventional art.

(2) Second Embodiment In this embodiment, a tap is provided in the series circuit of the delay circuits 8A to 8N in the first embodiment, and the tap output is selectively subtracted by the subtraction circuit. 9 can be input. The microphone device according to the second embodiment is the same as the microphone device according to the first embodiment except that the delay circuits 8A to 8N and the subtraction circuit 9 have different configurations. As a result, in this embodiment, the substantial number of stages n by the series circuit of the delay circuits 8A to 8N is set to n ≦ d / cτ.

As a result, in this embodiment, the arrival direction of the main audio data having the same phase as that of the sub audio data input to the subtraction circuit 9 can be switched variously. As a whole, the directivity of the whole can be switched variously.

According to the above configuration, in the configuration of the first embodiment, the delay time by the delay circuits 8A to 8N can be varied, so that in addition to the effect of the first embodiment, the directivity can be variously changed. Can be changed.

(3) Third Embodiment In this embodiment, in the configuration according to the first embodiment, it is obtained by adding main and sub voice data instead of main voice data. The added data is input to the delay circuit 14.

Even if the addition data obtained by adding the main and sub voice data is input to the delay circuit 14 and adaptively processed instead of the main voice data as in this embodiment. The same effect as that of the first embodiment can be obtained.

(4) Other Embodiments In the above-mentioned embodiments, the case where the microphone device is constituted by the non-directional microphones 2 and 3 has been described, but the present invention is not limited to this, and the directivity is not limited thereto. You may make it comprise a microphone apparatus with the microphone which has. In this case, in FIGS. 2A and 2B, the directivity of each microphone is shown by the polar pattern of sensitivity, and the microphones 2 and 3 are arranged so as to correspond to the directivity secured by the microphone device. By setting the orientation, the overall directivity can be made even sharper. Incidentally, FIG. 2A shows a case where directivity is ensured for a sound wave coming from the microphone 2 side on a straight line connecting the microphones 2 and 3.
(B) is a case where directivity is ensured for a sound wave that arrives at an angle of 45 degrees obliquely upward in the figure.

In the above embodiment, the LMS
The case where the tap coefficient of the adaptive filter is switched by the algorithm has been described, but the present invention is not limited to this, and various algorithms can be applied as necessary.

In the above embodiment, the case where the directivity is ensured by processing the main and sub audio signals obtained from the two microphones has been described, but the present invention is not limited to this and is necessary. According to the above, two or more microphones can be arranged linearly, in a matrix, and three-dimensionally, and can be widely applied when securing a desired directivity.

In the above embodiment, the case where the main and sub microphones 2 and 3 are simply arranged has been described, but the present invention is not limited to this, and these microphones 2 are provided so as to secure a desired directivity. A cylindrical member similar to that of the related art may be disposed in each of Nos. 3 and 3.

[0033]

As described above, according to the present invention, after the main audio signal obtained from the main microphone is delayed by a predetermined time, a subtraction signal is subtracted from the sub audio signal obtained from the sub microphone. Is generated and the main speech signal is adaptively processed using the subtraction signal as a reference input, the shape can be made smaller and sharp directivity can be secured as compared with the conventional case.

[Brief description of drawings]

FIG. 1 is a block diagram showing a microphone device according to an embodiment of the present invention.

FIG. 2 is a plan view showing the arrangement of microphones according to another embodiment.

[Explanation of symbols]

1 ... Microphone device, 2 ... Main microphone, 3
...... Sub microphone, 8A to 8N, 14 ... Delay circuit, 9, 15 ... Subtraction circuit, 11 ... Low-pass filter, 12 ... Adaptive processing circuit, 13 ... Adaptive filter

Claims (4)

[Claims] 1. A main microphone that outputs a main audio signal, a sub microphone that is arranged to be separated from the main microphone by a predetermined distance, and outputs a sub audio signal, and a predetermined delay. A delay circuit that delays and outputs the main audio signal for a time; a subtraction circuit that outputs a subtraction signal of the output signal of the delay circuit and the main audio signal; and a flattening frequency characteristic of the subtraction signal. A microphone device comprising: a filter circuit; and an adaptive processing circuit that adaptively processes the main audio signal using an output signal of the filter circuit. 2. The adaptive processing circuit, wherein an adaptive filter that corrects the output signal of the filter circuit by switching a tap coefficient based on the output signal by a predetermined algorithm, and an adaptive filter of the main audio signal is used. The microphone device according to claim 1, further comprising a subtraction circuit that subtracts an output signal. 3. The microphone device according to claim 2, wherein the predetermined algorithm is a least mean square algorithm. 4. The microphone device according to claim 1, wherein the delay circuit is formed so that the delay time can be varied.