JP2000278786A - Microphone system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a gain of a microphone from being decreased down to a degree causing difficulty in listening to voice due to a noise such as a breathing noise and to reduce fluctuation in a recording level and a loudspeaking level due to the fluctuation in the relative position between a talker and the microphone. SOLUTION: An analog voice signal from a microphone unit 110 is converted into a digital voice signal, which is given to a frequency band split filter section 130. The frequency band split filter section 130 uses a plurality of frequency band pass filters to divide the digital voice signal into a plurality of frequency bands. A level conversion circuit 140 receives each frequency band signal, applies level conversion to each frequency band signal for each band, synthesizes the band signals and provides an output. A control section 160 nonlinearly converts levels of each of the frequency band signals in the level conversion circuit 140 to decrease an amplification factor of the frequency band component with a higher input level and to increase an amplification factor of the frequency band component with a lower input level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microphone device used in the fields of, for example, loudspeakers, telephones, and voice communications, and more particularly to an improvement in a signal processing circuit in the microphone device.

[0002]

2. Description of the Related Art Conventionally, in a microphone device of this type, when transmitting and reproducing sound, when the dynamic range of a transmission system and a reproduction system is not sufficiently wide, the amplification factor of a low-level sound is increased and increased. An automatic gain control device (AGC) is used to control the gain of the level sound to be small.

[0003]

However, the above-mentioned conventional automatic gain control device has the following problems in setting and operation stability. (1) After breathing into the microphone, wind noise, or the impact sound of striking the microphone, etc., the gain may become small and the sound may not be heard. (2) When the direction of the speaker's face changes and voice enters from a direction deviating from the directional characteristics of the microphone, the sound radiation directional characteristics are sharper at higher frequencies than at lower frequencies. May be relatively low, and the sound may be unclear. (3) When listening to a voice that is louder in a noisy environment, small-level components such as consonants may be masked by noise, making it difficult to hear words.

It is an object of the present invention to prevent the gain of an automatic level control recorder or loudspeaker connected downstream of a microphone from becoming low until it becomes difficult to hear the sound due to noise such as breath noise, and Another object of the present invention is to provide a microphone device capable of reducing fluctuations in a recording level and a loud sound level due to fluctuations in a relative position between a speaker and a microphone.

[0005]

In order to achieve the above object, according to the present invention, there is provided a band dividing means for dividing a frequency band of an audio signal inputted from a microphone unit, and a signal inputted from the band dividing means for each band. Level conversion means for level-converting and outputting the signals, synthesizing means for adding and synthesizing the signals from the level conversion means for each band, and setting the input / output characteristics of the level conversion means for each band, thereby providing a specific band. Setting means for relatively suppressing the transmission of the component.

In the microphone device of the present invention, the component components of the input audio signal are divided into frequency bands, and the level is nonlinearly converted for each frequency band. For example, the level conversion is performed so that the amplification factor of the frequency band component having a large input level is small and the amplification factor of the frequency band component having a small input level is large, thereby suppressing the transmission of the component of the specific band. As a result, the main components of the sound can be put within the dynamic range of the microphone amplifier, power amplifier, loudspeaker, etc. at the subsequent stage, so that clear speech, transmission, recording, etc. can be performed without any special operation. It can be carried out.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a microphone device according to the present invention will be described. FIG. 1A is a block diagram schematically showing a configuration example of a microphone device according to the present invention. A digital signal processor (DS) having a built-in A / D and D / A converter for low-voltage operation is provided.
P) is shown. This microphone device includes a microphone unit 110 and an A / D converter 12.
0, a frequency band division filter section 130, a level conversion section 140, a D / A conversion section 150, and a control section 160, and includes a section from the A / D conversion section 120 to the D / A conversion section 150. The configuration is constituted by a DSP. Further, a power supply voltage of 1.5 V is supplied to each of the above units.

[0008] The microphone unit 110 has a microphone 112 and an amplifier 114.
2 is amplified by the amplifier 114 and output to the A / D converter 120. A / D converter 120
Converts an analog audio signal from the microphone unit 110 into a digital audio signal and outputs the digital audio signal to the frequency band division filter unit 130. Frequency band division filter unit 13
In the case of 0, the digital audio signal is divided into a plurality of frequency bands by a plurality of frequency band filters, and each frequency band signal is output to the level conversion circuit 140.

The level conversion circuit 140 performs level conversion on each frequency band signal for each band, synthesizes each band signal,
Output to D / A conversion section 150. D / A converter 150
Converts the digital signal of each band from the level conversion circuit 140 into an analog signal and outputs the analog signal. Control unit 160
Sets the input / output characteristics (level conversion rate) of the level conversion circuit 140. At this time, the utterance sound pressure level in the vicinity of a person is set to a reference input of a circuit connected to the subsequent stage of the microphone unit. Convert based on level.

That is, the control section 160 non-linearly converts the level of each frequency band signal in the level conversion circuit 140, reduces the amplification factor of the frequency band component having a large input level, and amplifies the signal in the frequency band having a small input level. By increasing the rate, the main components of the sound were placed within the dynamic range of the microphone amplifier, power amplifier, and loudspeaker in the subsequent stage, thereby suppressing breath noise and shock noise without any special operation. In this state, it is possible to clearly transmit the main components of the voice, and to perform clear loudspeaking, transmission, recording, and the like.

FIG. 1B is a block diagram showing in principle the processing elements of the frequency band division filter section 130 and the level conversion section 140 described above. As shown, in this device, the input audio signal S51 is divided into three frequency bands by three band-pass filters 54L, 54M, 54H, and the level conversion processing units 50L, 50M, 5
Level conversion is performed by 0H. Then, the output signals of the level conversion processing units 50L, 50M, 50H are added to the addition circuit 55.
And output. The processing of the frequency band division filter unit 130 described above is performed by the bandpass filters 54L and 54L.
M, 54H, and the processing of the level conversion unit 140 corresponds to the processing of the level conversion processing units 50L, 50M, 50H and the addition circuit 55.

Next, a method of controlling the level of the microphone device having the above configuration will be described. FIG.
FIGS. 2A and 2B are explanatory diagrams showing examples of a frequency component distribution and a time waveform of a voice at a mouth. In FIG. 2A, the vertical axis represents level (dB), and the horizontal axis represents frequency (kHz). 2B, the vertical axis represents level (V), and the horizontal axis represents time (m).
sec). FIGS. 3A and 3B are explanatory diagrams showing an example of a frequency component distribution and a time waveform of breath noise when a breath is blown on a microphone.
In FIG. 3A, the vertical axis indicates level (dB) and the horizontal axis indicates frequency (kHz). In FIG. 3B, the vertical axis indicates level (V) and the horizontal axis indicates time (msec). FIGS. 4A and 4B are explanatory diagrams showing examples of frequency component distribution and time waveform of an impact sound when an object hits the microphone. In FIG. 4A, the vertical axis represents the level (dB). ),
The horizontal axis indicates frequency (kHz), and in FIG. 4B, the vertical axis indicates level (V), and the horizontal axis indicates time (msec).

[0013] Breathing noise and the like have a higher level component in the low frequency band than the frequency component distribution of the voice. When the gain control of the entire signal is performed at the signal level of this component, the AGC circuit becomes Since it works so as to reduce the gain, the high-frequency components become small, making it difficult to hear. Therefore, in this example, the input voice is divided into frequency bands, and level conversion is independently performed for each band to perform gain control.

FIG. 5 is an explanatory diagram showing a specific example of frequency band division and gain control in the microphone device of the present embodiment. In this example, as the frequency band, the pitch and the band of the first formant component, the band of the second formant component,
It is divided into three bands of a third formant component and a consonant component. The boundary frequency of each band may be fixed or variable. In the case of a fixed boundary frequency, for example, 1.2
The frequency is divided into three at kHz and 3.2 kHz. Then, as shown in the figure, the lower the band, the smaller the amplification factor of the output level with respect to the larger input level, thereby suppressing the transmission of the frequency component of the low band. In this way, the gain of other frequency components does not decrease due to a large-level low-frequency component due to breath noise or the like.

By the way, the actual value of the gain control of each band when the frequency band is divided in this way is determined by the sound pressure-voltage conversion sensitivity of the microphone unit, the gain of the microphone amplifier, the transmission line at the subsequent stage, the recorder, the loudspeaker, etc. And so on. Therefore, in the following description, the gain control method for the audio signal for each frequency band will be described by replacing the input sound pressure level-output sound pressure level characteristic diagram. Normally, the close-talking microphone is used in such a manner as to approach the mouth and pick up sound. The speech sound level at the mouth is about 95 dB. This level may be considered as the center of the input level, and the input level may be converted to the output level.

FIG. 8 is an explanatory diagram showing an example of level conversion when a relative position change between the head of the user of the close-talking microphone and the close-talking microphone and a change in voice volume are considered.
The sound pressure level of a normal voice at the mouth is about 95 dB, about 115 dB for a loud voice, and about 75 dB for a small voice. In the example of FIG. 8, the level is converted around 65 dB, which is a sound pressure level (comfortable listening level) that is usually easy to hear. Note that the absolute value of the level after conversion differs depending on the device using the microphone device of the present example. For example, when the microphone device is connected to a loudspeaker that inputs a line level, the output level of 65 dB in FIG. 8 is made to correspond to the reference input level of the loudspeaker at the subsequent stage.

FIG. 6 is an explanatory diagram showing two examples of general input level-output level conversion characteristics. As shown by the broken line in FIG. 6A, the smaller the slope of the characteristic diagram, the greater the degree of level compression, and as shown by the broken line in FIG. This means that the degree of amplification is large. As shown in FIG. 6A, when looking at the characteristic diagram of the level compression setting with respect to the input level, the amplification factor is higher when the input level is lower than when the input level is higher. Also,
In order to change the nonlinear level conversion operation depending on the input level range, a bending point such as point A in FIG. 7 may be provided. Usually, this point A is called "knee point"
Call.

In the case shown in FIG. 6, at an input level larger than the point A, the dynamic range is compressed and converted, and at an input level smaller than the point A, the dynamic range is expanded and converted. In addition to the point A, the point B for limiting the maximum output level of the level conversion characteristic is called an “output restriction point”, and the point C for determining the level conversion characteristic at a low input level is referred to as “background noise”. We call it the "suppression point." Note that P
When a signal from a microphone is amplified, output from a speaker, and forms a feedback loop to be input again to the microphone as in the device A, an oscillation phenomenon commonly called howling occurs. Therefore, in order to prevent oscillation due to this loop, an amplification gain limit as shown by a dashed line in FIG. 7 is provided to limit the moving range of the knee point. In the microphone device of this example, the output sound pressure level after the level conversion is controlled so as to be about 65 dB, which is an ideal comfortable listening level, while taking the above conditions into consideration.

As described above, in the microphone device of the present embodiment, by performing level conversion for each audio signal divided into frequency bands, when picking up sound with the close-talking microphone, excessively large frequency components are suppressed, and inversely. Level conversion to increase the small frequency components. Therefore, when the relative position between the speaker's mouth and the microphone cannot be stably maintained, even if the positional relationship between the mouth and the microphone is displaced, it is not necessary to perform level correction by volume control. In addition, even when the microphone is used in a situation where wind noise or impact sound is likely to enter the microphone or when the listening environment is noisy, there is no need to correct the level or frequency characteristics corresponding to the wind noise or impact sound entering the microphone. Further, it is possible to obtain a clear voice sound.

The above-described level compression / amplification operation may be performed on an instantaneous level. However, since the output waveform is greatly distorted, a large level is often input with respect to the immediately preceding level. In such a case, it has been proposed that the operation of suppressing the amplification factor is performed instantaneously, and conversely, when a level smaller than the immediately preceding level is input, the operation of increasing the amplification factor is performed with a time delay. See, for example, Japanese Patent Application No. 10-183829. Therefore, it is also possible to combine a circuit in which such a level compression amplification operation has a time difference in accordance with a change in input level with a level conversion processing function by frequency band division according to the present invention.

FIG. 9 is a block diagram showing in principle the configuration of a circuit for performing a level compression / amplification operation including a delay operation in accordance with a change in the input level. This circuit is, for example, shown in FIG.
Level conversion processing units 50L, 50M, 50 shown in (B)
H. In FIG. 9, the input audio signal divided in the frequency band as described above is supplied to a gain control amplifier 52 through an input terminal 51, the level is converted in the gain control amplifier 52, and then output to an output terminal 53.

The audio signal from the input terminal 51 is supplied to a level detection circuit 61 comprising a rectifier circuit 611 and a low-pass filter 612, and a signal indicating the envelope of the input audio signal, that is, the instantaneous level of the input audio signal Is detected. Then, this detection signal is supplied to the control signal forming circuit 63 and the delay circuit 62. The delay circuit 62 outputs a delay signal corresponding to the detection signal to the control signal forming circuit 63, and the control signal forming circuit 63 outputs a control signal to the gain control amplifier 52 based on the detection signal and the delay signal. The control signal from the control signal forming circuit 63 is determined based on the above-described gain setting value for each frequency division band.

With such a configuration, when a level higher than the immediately preceding level is input, the operation of reducing the amplification factor is performed instantaneously, and when a level smaller than the immediately preceding level is input, the amplification is performed. The operation of increasing the rate can be performed with a delay. In an actual device, the main elements of the circuit shown in FIG. 9 are the DS shown in FIG.
It is assumed that it is constituted by P.

[0024]

As described above, in the microphone device of the present invention, the audio signal input from the microphone unit is divided into frequency bands, and the level is converted based on the input / output characteristics set for each band. By synthesizing and outputting the level conversion signals for each, the transmission of the specific band component is relatively suppressed.

Therefore, when voice is picked up by the microphone, it is possible to perform level conversion for suppressing the excessively large frequency components and increasing the small frequency components, and connecting the microphone to the subsequent stage due to noise such as breath noise. To prevent the gain of the automatic level control recorder or loudspeaker from lowering until it becomes difficult to hear the sound, and to reduce the fluctuation of the recording level and the loudspeaker sound level due to the fluctuation of the relative position between the speaker and the microphone. can do.

Therefore, for example, when the relative position between the mouth of the speaker and the microphone cannot be stably maintained, even if the positional relationship between the mouth and the microphone is displaced, it is not necessary to correct the level by operating the sound volume. In addition, even when the microphone is used in a situation where wind noise or impact sound is likely to enter the microphone or when the listening environment is noisy, there is no need to correct the level or frequency characteristics corresponding to the wind noise or impact sound entering the microphone. Further, it is possible to obtain a clear voice sound.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram showing an example of a frequency component distribution and a time waveform of a voice at a mouth.

FIG. 3 is an explanatory diagram illustrating an example of a frequency component distribution and a time waveform of breath noise when a breath is blown on a microphone.

FIG. 4 is an explanatory diagram showing an example of a frequency component distribution and a time waveform of an impact sound when an object hits a microphone.

5 is an explanatory diagram showing a specific example of frequency band division and gain control in the microphone device shown in FIG.

FIG. 6 shows a general input level-output level conversion characteristic 2
It is explanatory drawing which shows two examples.

FIG. 7 is an explanatory diagram showing an example of an input level-output level conversion characteristic provided with a knee point and the like.

FIG. 8 is an explanatory diagram showing an example of an input level-output level conversion characteristic used in the microphone device shown in FIG.

FIG. 9 is a block diagram illustrating a configuration example of a level conversion processing unit of a microphone device according to an application example of the present invention.

[Explanation of symbols]

110 microphone unit, 120 A / D conversion unit, 130 frequency band division filter unit, 140
... Level conversion unit, 150 D / A conversion unit, 160
Control unit.

Claims (7)

[Claims] 1. Band dividing means for dividing a frequency band of an audio signal input from a microphone unit, level converting means for level converting a signal input from the band dividing means for each band, and outputting the same. Synthesizing means for adding and synthesizing signals from each level converting means, and setting means for relatively suppressing transmission of components in a specific band by setting input / output characteristics of the level converting means for each band, A microphone device comprising: 2. The method according to claim 1, wherein the specific band is a frequency band having a large input level, and the setting unit increases a gain of a frequency band component having a large input level and increases a gain in a frequency band having a small input level. 2. The microphone device according to claim 1, wherein: 3. The microphone device according to claim 1, wherein the specific band is a frequency band lower than a frequency for transmitting a main component of a voice. 4. The input / output characteristic of the level conversion means, such that the output sound pressure level after the level conversion by the level conversion means becomes a reference input level of a circuit connected to a subsequent stage of the microphone. The microphone device according to claim 1, wherein the microphone device is set. 5. The apparatus according to claim 1, wherein said setting means sets the input / output characteristics of said level converting means so that the dynamic range of the audio signal of each frequency band is compressed by said band dividing means. Microphone device. 6. The operation of the level conversion means is performed instantaneously when a level higher than the immediately preceding level is input, and is performed with a certain delay when a level lower than the immediately preceding level is input. The microphone device according to claim 1, wherein 7. The apparatus according to claim 1, wherein said band dividing means, said level converting means, said synthesizing means, and said setting means include an A / A
The microphone device according to claim 1, further comprising a digital signal processor having a D / A conversion unit and a D / A conversion unit at an output unit.