JPH11187478A - Microphone system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microphone system by summing output signals from each omnidirectional microphone, while delaying their phases respectively so as to reduce noises inside the system and wind noises, without inverting the phase of a low frequency component thereby picking up sound with a high S/N ratio. SOLUTION: A second omnidirectional microphone 2 is placed at a position behind a first omnidirectional microphone 1 by 12 mm. A phase shifter 3 for providing a phase delay angle of 90-degree at a frequency of 338 Hz delays the phase of an output signal of the first omnidirectional microphone 1. A phase shifter 4 for providing a phase delay angle of 90-degree at a frequency of 10.6 kHz delays a phase of an output signal of the second omnidirectional microphone 2. An adder 5 sums output signals of the phase shifters 3, 4 in-phase. An equalizer 6 corrects the frequency characteristic of an output signal of the adder 5 and provides an output of the corrected result.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microphone device incorporated in a device having a noise source therein, and more particularly to a microphone device incorporated in a video integrated camera or the like.

[0002]

2. Description of the Related Art Japanese Patent Laid-Open Publication No. HEI 9 (1999) discloses a microphone device with a built-in main body capable of reducing the influence of noise and vibration generated by a mechanical system in a video-integrated camera main body and wind noise and capable of collecting sound having a high S / N. It is proposed in JP-A-4-322598.

FIG. 5 is a block diagram of a conventional microphone device proposed in the above publication. The conventional microphone device removes low-frequency components of output signals of the first and second omnidirectional microphones 11 and 12 and the first omnidirectional microphone 11 that are arranged on a straight line with an interval therebetween. A high-pass filter (HPF) 13, a phase shifter 14 for delaying the phase of the output signal of the second omnidirectional microphone 12, and an output of the phase shifter 14 mixed with the output of the high-pass filter (HPF) 13 in opposite phases. It is composed of a subtractor 15 and an equalizer (EQU) 16 for correcting the frequency characteristics of the output signal of the subtractor 15.

In a conventional microphone device, a low-frequency component of an output signal of a first omnidirectional microphone 11 is removed by a high-pass filter (HPF) 13 and a phase of an output signal of a second omnidirectional microphone 12 is shifted. The output signal of the high-pass filter (HPF) 13 is delayed by the phase shifter 14, the output signal of the phase shifter 14 is added in reverse phase to the output signal of the high-pass filter (HPF) 13, and the frequency characteristic is corrected by the equalizer (EQU) 16 and output.

[0005]

In the conventional microphone device, a signal whose phase has been delayed by the phase shifter 14 is added to the signal from which the low-frequency component has been removed by the high-pass filter (HPF) 13 in reverse phase. The signal in the frequency range is inverted. Therefore, when the output signal of the conventional microphone device is mixed with the output signal of another sound collection device, the signal level in the low frequency range may be reduced, or in the worst case, the audio output may not be obtained. There is.

[0006] Even if wind noise whose frequency components are concentrated in the low frequency region is collected by the omnidirectional microphones 11 and 12,
A low-frequency component related to wind noise collected by the first omnidirectional microphone 11 is a high-pass filter (HPF) 13.
As a result, the wind noise collected by the second directional microphone 12 out of the two omnidirectional microphones 11 and 12 is output. For this reason, the wind noise can be set to the same level as the omnidirectional microphone, but this does not reduce the wind noise.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and delays and adds the phase shifts of the output signals of the omnidirectional microphones to add noise and wind noise from the inside of the device to a low frequency band. It is an object of the present invention to provide a microphone device capable of reducing a phase of a frequency component without inverting the same and collecting sound with a high S / N.

[0008]

In order to solve the above-mentioned problems, a microphone device according to the present invention comprises a first and a second omnidirectional microphones arranged linearly at an interval from each other, and a first microphone. , A first phase shifter for delaying the phase of the output signal of the second microphone, a second phase shifter for delaying the phase of the output signal of the second microphone, and an addition for in-phase addition of the outputs of the first and second phase shifters And a container.

In the microphone device according to the present invention, the output signal of each microphone is phase-shifted by each phase shifter, and each signal whose phase is delayed by each phase shifter is added by an adder. Therefore, the phase of the signal in the low frequency range is not inverted.
Therefore, when the output signal obtained by collecting the same sound source by the microphone device according to the present invention and the output signal obtained by collecting the sound by another sound collection device are mixed, the signal level in the low frequency range becomes low. Mixing can be performed satisfactorily without problems such as lowering.

[0010] By delaying the phase of each output signal of each omnidirectional microphone arranged at a predetermined interval on a straight line and then adding the signals in phase, the omnidirectional characteristics at low frequencies are reduced, and the characteristics of middle and high frequencies are reduced. In this case, a unidirectional characteristic having a low response in the 180-degree direction can be obtained.
Therefore, when the microphone device according to the present invention is applied to a video-integrated camera, it is possible to reduce the effects of harsh and high-frequency band noise generated from a mechanical system in the video-integrated camera.

By performing the in-phase addition at the low frequency band, wind noise distributed in a low frequency band of 200 Hz or less having low correlation between the outputs of the non-directional microphones can be averaged. Therefore, the influence of wind noise can be reduced.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram of a microphone device according to the present invention. The microphone device according to the present invention includes a first and a second omnidirectional microphones 1 and 2 which are arranged on a straight line at an interval from each other, and a second device which delays a phase of an output signal of the first omnidirectional microphone 1. 1 phase shifter 3, a second phase shifter 4 that delays the phase of the output signal of the second omnidirectional microphone 2, and an adder 5 that adds the output signals of the phase shifters 3 and 4 in-phase. And an equalizer (EQ) for correcting the frequency characteristic of the output signal of the adder 5.
U) 6.

A second omnidirectional microphone 2 is arranged behind the first omnidirectional microphone 1. A predetermined distance d between the first and second omnidirectional microphones 1 and 2
(For example, 12 mm). The microphones 1 and 2 are directed in the direction between the microphones in the imaging direction of the video-integrated camera (the front direction of the video-integrated camera), with the microphone 1 forward and the microphone 2 backward.
Is arranged. In a stereo recording type video-integrated camera having a different mounting form from the above, two sets of microphone devices according to the present invention are provided on the left and right, and the microphones are arranged so that the direction between the microphones is the front direction of the video-integrated camera. I do. In addition, each microphone of the left channel is arranged so that the direction between the microphones is directed more leftward than the front direction of the video-integrated camera, and each microphone of the right channel is positioned such that the direction between the microphones is more than the front direction of the video-integrated camera. May be arranged so as to be directed rightward.

The microphone device according to the present invention has a first
The phase of the output signal of the omnidirectional microphone 1 is delayed by the first phase shifter 3, and the second omnidirectional microphone 2
Is delayed by a second phase shifter 4, the output signals of the phase shifters 3 and 4 are added in phase by an adder 5, and the signal obtained by the in-phase addition is frequency-converted by an equalizer (EQU) 6. Correct the characteristics and output.

The sensitivity of the first omnidirectional microphone 1 is A, the sensitivity of the second omnidirectional microphone 2 is B, the phase characteristic of the first phase shifter 3 is ψa (ω), and the second phase shift is位相 b (ω), the angle between the direction between the microphones and the sound source (not shown) is θ, the distance between the microphones is d,
Assuming that the sound speed is C, the combined output P output from the adder 5
Is represented by Equation 1. Note that ω represents each frequency (ω = 2π
f).

[0016]

(Equation 1)

When the sensitivity A of the first omnidirectional microphone 1 is equal to the sensitivity B of the second omnidirectional microphone 2, the combined output P is simplified to the following equation (2).

[0018]

(Equation 2)

Further, the directivity pattern D (θ) is expressed by Expression 3.

[0020]

(Equation 3)

FIG. 2 is a graph showing the phase characteristics of the phase shifter. The vertical axis represents the phase angle in radians, and the horizontal axis represents the normalized angular frequency (ω / ω0).

Here, the first and second phase shifters 3 and 4
In addition, at the reference angular frequency ω0 shown in FIG.
Using a phase shifter with a characteristic of 2 radians (90 degrees),
The reference angular frequency ωa0 at which the characteristic of the phase shifter 3 is −π / 2 radians (−90 degrees) is 338 Hz (Hertz), and the characteristic of the second phase shifter 4 is −π / 2 (−90 degrees). When the reference angular frequency ωb0 is 10.6 KHz (kilohertz), the distance d between the non-directional microphones 1 and 2 is 12 mm (millimeter), and the sound speed C is 344 m / s (meter / second), FIG. 3 shows the frequency-response characteristics at the output of the adder using the angle θ formed with the sound source as a parameter, and FIG. 4 shows the directional characteristics at 4 KHz (kilohertz).

As shown in FIGS. 3 and 4, the microphone device according to the present invention has a low frequency (300 Hz or less).
, A non-directional characteristic can be obtained, and a unidirectional characteristic having a low response in the 180-degree direction can be obtained at middle and high frequency bands.

[0024]

As described above, in the microphone device according to the present invention, the output signal of each omnidirectional microphone is phase-shifted by each phase shifter, and each signal whose phase is delayed by each phase shifter is added to the adder. , The phase of the signal in the low frequency range is not inverted. Therefore, when the output signal obtained by collecting the same sound source by the microphone device according to the present invention and the output signal obtained by collecting the sound by another sound collection device are mixed, the signal level in the low frequency range becomes low. Mixing can be performed satisfactorily without problems such as lowering.

According to the present invention, the microphone device is configured to delay the phase of each output signal of each omnidirectional microphone arranged at a predetermined interval on a straight line, and then to add in-phase signals. Characteristic can be obtained, and a unidirectional characteristic having a low response in the 180-degree direction can be obtained at middle and high frequencies. Therefore, when the microphone device according to the present invention is applied to a video-integrated camera, it is possible to reduce the effects of harsh and high-frequency band noise generated from a mechanical system in the video-integrated camera.

By performing the in-phase addition at the low frequency band, it is possible to average the wind noise distributed in the low frequency band of 200 Hz or less where the correlation between the outputs of the omnidirectional microphones is low. Therefore, the influence of wind noise can be reduced.

[Brief description of the drawings]

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

FIG. 2 is a graph showing phase characteristics of a phase shifter.

FIG. 3 is a graph showing a frequency response characteristic of the microphone device according to the present invention.

FIG. 4 shows a 4 KHz microphone device according to the present invention.
Graph showing directional characteristics in kilohertz

FIG. 5 is a block diagram of a conventional microphone device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... 1st omnidirectional microphone, 2 ... 1st omnidirectional microphone, 3 ... 1st phase shifter, 4 ... 2nd phase shifter,
5 ... Adder, 6 ... Equalizer.

Claims (1)

[Claims] A first phase shifter that delays a phase of an output signal of the first microphone; a first phase shifter that delays a phase of an output signal of the first microphone; A microphone device comprising: a second phase shifter that delays the phase of an output signal of the second microphone; and an adder that adds the outputs of the first and second phase shifters in phase.