JPH11150784A - Microphone system composed of plural partial band microphones - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a microphone system with which a high dynamic range can be provided over a wide band. SOLUTION: This system is composed of (n) pieces (n) is an integer >=2} of microphone groups 11-13 for performing electric transformation of sounds in a prescribed partial band and a synthesizing means 700 for synthesizing these A/D converted (n) pieces of outputs, so that digital codes over all the bands are extracted. It is preferable that the system is composed of a ΔΣ modulator for ΔΣ modulation with prescribed band characteristics and a decimation filter for thinning sampling data while limiting bands with the respective prescribed frequency characteristics. The microphone system is provided by improving stability through A/D converting elements 1000, 2000 and 3000 and providing a high dynamic range over wide bands through mutual complementary operations of the microphone groups 11-13 specified on the prescribed band.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microphone device for converting a wideband sound from a low frequency to an ultrasonic wave into an electric signal and further converting the signal into a digital code, and more particularly, to a plurality of partial band microphones and a plurality of AD conversion elements. The present invention relates to a microphone device that realizes high S / N and wideband conversion using the same.

[0002]

2. Description of the Related Art There are various types of microphones. In particular, microphones mainly used for voice and music recording have been developed specifically for a frequency band determined by the characteristics of conventional recording media, and have a frequency range of up to 20 kHz. It has been a general purpose to improve the noise spectrum, dynamic range, and frequency characteristics in the frequency band, and to take into account the taste of the collected sound color. Therefore, with this type of microphone, an output signal in a frequency band of 20 kHz or more was not obtained, or even if it was obtained, it was of low quality.

[0003] Alternatively, some microphones have been developed for the purpose of measuring acoustic energy over the band up to ultrasound. This was used for a sound level meter for measuring noise. In some cases, the frequency response was flattened over the band up to 100 kHz, but in order to convert sound to electrical energy without causing split vibration even in the ultra-high frequency range, the size of the diaphragm must be reduced. was there. However, when the size of the diaphragm is reduced, the conversion efficiency is reduced, so that a sufficient electric signal output cannot be obtained, and the SN ratio and the dynamic range are insufficient.
It was not used for voice or music recordings.

[0004]

However, with the advent of DVDs in recent years, a sampling frequency of 96 kHz and a quantization bit number of 24 bits have been put to practical use in order to make use of the high density to achieve higher sound quality. Further, various attempts to record and reproduce a band up to approximately 100 kHz are being made. In other words, although there is a possibility that the infrastructure as a recording / reproducing medium is ready, there is a problem that the essential sound collection quality is still insufficient. Conventional microphones have not yet achieved sufficient performance to meet their specifications. More specifically, there are the following problems.

[0005] (A) If a wide band is designed so as to cover up to 100 kHz in one way, the output is reduced and the S / N ratio and the dynamic range are reduced. Therefore, a sufficient wide band cannot be achieved and the dynamic range tends to be reduced. become.

(B) If a high output is used in order to obtain a high SN ratio in one way, clipping distortion occurs at a high sound pressure level, so that conversion cannot be performed. Bandwidth. On the other hand, if sufficient headroom is provided to prevent clipping distortion at a large sound pressure level, there is a problem that the signal level intensity with respect to the noise spectrum in a wide band becomes insufficient and the SN ratio decreases.

(C) Some multi-way microphones use a plurality of microphones. However, the characteristics are varied and unstable due to band division and synthesis by an analog amplifier.

(D) In a multi-way microphone using a plurality of microphones, a signal obtained by synthesizing a plurality of signals by an analog amplifier is converted into a digital signal by an A / D converter. Has been difficult to obtain.

An object of the present invention is to solve the above-mentioned problem, and an object of the present invention is to provide a wide-band, high-dynamic-range microphone that can prevent variation, deterioration of stability, and noise.

[0010]

In order to achieve this object, a microphone device according to the present invention comprises a plurality of microphones for converting input acoustic energy into electric signals in a predetermined partial band, and a plurality of microphones for converting digital signals into digital codes. , And a synthesizing means for synthesizing the output of each AD conversion element to extract digital codes of all bands.

Thus, a high dynamic range can be obtained over a wide band.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A microphone device according to a first aspect of the present invention provides a microphone device which receives analog signals input from i (i is an integer of 2 or more) microphones each having characteristics suitable for a predetermined partial band. N (where n is an integer of 2 or more) AD conversion elements for converting to digital codes in the partial band, and n outputs of the AD conversion elements are combined to form m bits (m satisfies 2 ^m ≧ n + 1) Positive integer)
And a synthesizing means for converting the m-bit digital code from the synthesizing means.

Further, the AD converter of the microphone device according to the second aspect of the present invention is a ΔΣ modulator for ΔΣ modulating an input analog signal with a predetermined band characteristic, and the ΔΣ modulator.
A decimation filter that limits the band of each output of the modulator with a predetermined frequency characteristic and thins out sampling data, and the decimation filter passes mainly in a predetermined band of the ΔΣ modulator to be connected, and passes other bands. In addition to the above, the transmission characteristics having the opposite characteristics are convolved in accordance with the frequency characteristic, the phase characteristic, or the group delay characteristic between the i input signals and the variation therebetween. Things.

According to the present invention, as described above, each microphone can obtain an optimum characteristic in each band, and the AD conversion element to be combined is a predetermined clock using a relatively low clock and a low-order feedback filter. , The dynamic range in the divided band can be increased, and stabilization can be achieved. These AD conversion elements are combined with a decimation filter that passes through a predetermined band and blocks out of the band, and removes noise outside a predetermined divided band. Furthermore, by combining the outputs of a plurality of AD conversion elements that obtain predetermined performance in different bands, a wider band and a higher dynamic range can be achieved as a whole. In addition, n ADs
When the outputs of the conversion elements are combined, the rise and fall appearance probabilities of the ΔΣ modulation waveform are substantially balanced, so that an operation of geometrically averaging conversion errors due to jitter occurs, and the effect of reducing noise due to jitter is secondary. Occurs.

Further, it becomes possible to convolve the optimum characteristics individually so as to be suitable for each microphone.

[0016]

Embodiment 1 Embodiment 1 of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic block diagram showing a microphone device according to a first embodiment of the present invention. Here, in consideration of future development, an embodiment according to the present invention of a microphone device which collects an acoustic signal from DC to 100 kHz and converts it into a digital signal is described. Therefore, the output signal is a digital code having a sampling frequency of 192 kHz and 24 bits. In the figure, 11, 12 and 13 are microphones, 101, 102 and 103 are analog input terminals,
1000 is an AD conversion element (a), 2000 is an AD conversion element
(b) 3000 is an AD conversion element (c), 7000 is a synthesizing means, and 710 is a digital output terminal. Note that the number entered without a leader line beside the signal line indicates the number of bits.

The microphone 11 is about 30 kHz from DC.
A microphone used in the band up to z. The microphone 12 is a microphone having excellent characteristics in a band of 20 kHz to 50 kHz. Microphone 13 is 5
The microphone has excellent characteristics in a band of 0 kHz or more. The microphone 11 has a diaphragm having a relatively large diameter, and the microphone 13 has a relatively small diameter. This is because, in the microphone 13 in particular, the resonance point frequency and the anti-resonance point frequency due to the divided vibration of the diaphragm are increased to optimize the characteristics in the ultrasonic band. However, sensitivity tends to decrease due to the small aperture.

An output signal of the microphone 11 is an input signal X1 from an input terminal 101, and an AD conversion element (a) 1000
To supply. Similarly, the signal of the microphone 12 is supplied to the AD conversion element (b) 2000 through the input terminal 102. Similarly, the microphone 13 has an AD conversion element (c) 30
Supply to 00. In each AD conversion element,
AD conversion is performed by the ΔΣ modulators 100, 300, 500 and the decimation filters 200, 400, 600, respectively.
AD converter (a) 1000, AD converter (b) 2000
And the output Wa701, W of the AD conversion element (c) 3000
b702 and Wc703 are supplied to the synthesis means 7000. The combining means 7000 outputs these three inputs Wa, Wb
And Wc are added and synthesized and output as an output signal W from an output terminal 710.

FIG. 2 is an internal block diagram of the AD converter (a) 1000. In the figure, 110 is an adder, 120 is a quantizer, 140 is a subtractor, 150 is a feedback filter, 210
Is the first FIR1 (finite impulse response) filter
(a) and 220 are second FIR2 filters (a). An analog input signal X input from an input terminal 101 is supplied to a quantizer 120 through an adder 110. One-bit quantization is performed at an oversampling frequency of 3072 kHz. The other input signal of the adder 110 is the quantization noise Q supplied from the feedback filter 150. The quantizer 120 quantizes the input analog signal into one bit. The quantized 1-bit signal is transmitted to the decimation filter 200 and input to the subtractor 140. The subtractor 140 outputs a difference signal between the input signal and the output signal of the quantizer 120, that is, a quantization noise Q.
The sampling frequency of 3072 kHz is a value selected in consideration of the current device performance, and if it is higher or lower than this value, the performance such as the dynamic range obtained is reduced. This quantization noise Q is converted in frequency and / or phase characteristics by a feedback filter 150 having a transfer characteristic Ha (z), and is returned to the adder 110. Here, when the signal Ya is represented by an equation, Ya = X + (1-Ha (z)) * Q, and the signal Ya is a component of the input signal X and a component fed back by the transfer characteristic Ha (z) of the quantization noise Q. Is the sum of Therefore, the spectrum conversion of the quantization noise Q can be performed by the transfer characteristic Ha (z). It is preferable to provide a pass characteristic so that the transfer function becomes 1 in a practical low frequency range, and to provide an attenuation characteristic in a high frequency range outside the practical band.
For example, LPF corresponds to this. The quantization noise Q can be driven to a high band outside the practical band by the ΔΣ modulation by the feedback loop. The 1-bit signal subjected to the predetermined spectrum conversion in this manner is output from the output terminal 710 to the output signal Y.
It is output to the decimation filter 200 of the next stage as a.

In the decimation filter 200,
A 1-bit 3072 kHz signal is converted to an FIR1 filter 21.
Decimates to 1/4 at 0 and 768kHz at 24 bits
Down-sampling and multi-bit,
The data is further decimated to 1/4 by the FIR2 filter 220 and converted into a 24-bit output 192 kHz Wa.

The internal configuration and operation of AD converter (b) 2000 and AD converter (c) 3000 in FIG. 1 are the same as those of AD converter (a) 1000 described in FIG. The differences are that the noise shape characteristics of the ΔΣ modulator, more specifically, the transfer functions of the feedback filters are different from each other, and that the band characteristics of the decimation filter are different. Hereinafter, these characteristics will be described.

FIG. 3 is a diagram for explaining a signal spectrum and a noise spectrum of the ΔΣ modulator. FIG. 3A shows ΔΣ
The output Ya of the modulator 100, FIG.
3C and the output Yb of the ΔΣ modulator 500 are shown in FIG.
The characteristic of c is shown. Note that the horizontal axis is the frequency axis, which is logarithmically shown for viewing a wide range.

In FIG. 3 (a), S1 is the signal spectrum of the input signal X1, and Na is the noise spectrum of the quantization noise driven to a higher frequency by Δ 域 modulation. 3072 of 16fs with sampling frequency 192kHz as fs
Oversampling is performed at kHz, and ΔΣ modulation is performed by a feedback loop to drive the quantization noise Q to a high band outside the signal band. Therefore, the noise spectrum becomes a mountain shape having a peak around the Nyquist frequency of 1536 kHz (8 fs). The value of oversampling ratio 16 is not enough to obtain a dynamic range of 24-bit accuracy over the entire signal band.
ΣModulation causes fatal defects such as deterioration of stability and oscillation. Therefore, in the present embodiment, a second-order or fourth-order low-order feedback filter is employed so as to always operate stably. Instead, the band for obtaining a dynamic range with 24-bit accuracy is narrowed. In FIG. 3A, a dynamic range of 24-bit accuracy is obtained in a band up to 24 kHz, and even within the band, the dynamic range is from 24 kHz to 96 kHz.
The dynamic range in the range is somewhat bad.

Next, FIG. 3B will be described. FIG. 3 (b)
3 also controls the quantization noise in the same manner as in FIG. The difference from FIG. 3A is that the feedback filter has a frequency of 24 kHz to 48 kHz.
The point is that a bandpass filter that passes Hz and blocks other bands is used. A band-pass filter can be obtained, for example, by optimally distributing the poles and zeros of the transfer characteristic Hb (z) of the feedback filter at frequencies other than DC. These make the noise spectrum Nb
Becomes The signal spectrum S0 is flat. In this manner, a dynamic range of 24-bit accuracy is obtained at 24-48 kHz.

FIG. 3C is the same as FIGS. 3A and 3B.
In FIG. 3C, a dynamic range with a 24-bit accuracy is obtained in a frequency band of 48 to 96 kHz.

These three signals, Ya, Yb and Yc
Are flat in the band up to 96 kHz for the input signal X, but are output to the next stage as signals containing different noise spectra. Ya is supplied to the decimation filter 200, Yb is supplied to the decimation filter 400, and Yc is supplied to the decimation filter 600, and thinning and filtering are respectively performed. Decimation is performed using an FIR filter having no group delay distortion, and aliasing distortion due to downsampling is 100%.
Sufficient characteristics are provided to prevent mixing in the kHz band.

FIG. 4 shows the characteristics of the decimation filter and also shows the noise spectra included in the signals Ya, Yb and Yc. In the figure, Fa is the frequency characteristic of the decimation filter 200, Fb is the frequency characteristic of the decimation filter 400, and Fc is the frequency characteristic of the decimation filter 400. In addition, Na is a noise spectrum included in the signal Ya, and Nb and Nc are noise spectra included in the signal Yb and the signal Yc, respectively. As shown in FIG. 4, the characteristics of the decimation filter do not merely remove out-of-band components that cause aliasing. Preferably, the respective decimation filters are combined so that only signals in a low noise spectrum region in each band are passed. By doing so, 96 kHz
Even within the band equal to or less than z, the raised portion of the noise spectrum is filtered, and the rise of noise can be suppressed. In the figure, the broken line portion of the curve indicating the magnitude of the noise spectrum Na indicates a portion that is attenuated by the decimation filter 200. Similarly, similarly, the broken lines of the curves representing the noise spectrum Nb and the noise spectrum Nc indicate the portions attenuated by the decimation filter 400 and the decimation filter 600, respectively. The signal Wa, signal Wb, and signal Wc of 192 kHz / 24 bits obtained by down-sampling in this manner are supplied to the combining means 7000.

FIG. 5 is an internal block diagram of the synthesizing means 7000. Signals Wb and Wc having relatively small signal levels
Is added by the adder 720, and the result and the signal Wa are added to the adder 7
At 10, the signals are added and synthesized, and output to an output terminal 710 as an output signal W.

FIG. 6 is a diagram showing the overall frequency characteristics of the output signal W with respect to the input signal X. S in the figure is the characteristic of the signal component, and Na, Nb and Nc are the characteristics of the residual noise. From the figure, it can be seen that a dynamic range and SN ratio of 146 dB or more can be obtained in a band from DC to 96 kHz.

As is clear from the above description, such excellent characteristics are obtained by using a relatively narrow-band microphone and an A / D conversion element in combination in a partial band. The element can be realized by a relatively low-order feedback filter. Therefore, each AD conversion element always operates stably with respect to an input of any strength. For example, it is possible to prevent the oscillation from becoming unstable at a substantially full-scale input, or the occurrence of a small amplitude oscillation phenomenon (peep sound) due to a rounding error of an internal operation or the like in a DC input, in other words, in a DC offset state. . In addition, regarding the signal transmission characteristics, the AD conversion element, which originally has flat characteristics in the entire band, is divided into a plurality of partial bands by a digital decimation filter, and these are digitally added and synthesized.
Frequency continuity and phase continuity can be easily achieved by appropriately selecting the operation word length.

Further, since the outputs of the plurality of ΔΣ modulators and the decimation filter are added and synthesized by the synthesis means, the signal components are added and synthesized according to the transfer characteristics. For example, since the noise is attenuated by about 3 dB, there is also a side effect that the noise is reduced particularly near the boundary of the partial band, and the overall dynamic range and the SN ratio are slightly improved.

(Embodiment 2) Next, Embodiment 2 of the present invention will be described with reference to the drawings.

FIG. 7 is a schematic block diagram showing a microphone device according to the second embodiment of the present invention. In the figure, reference numeral 11 denotes a first microphone (simply referred to as a microphone in the figure), reference numeral 12 denotes a second microphone, reference numeral 101 denotes an input terminal for inputting a signal from the microphone 11, and reference numeral 102 denotes a signal for inputting a signal from the microphone 12. Input terminal.
Others are the same as the first embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals, and detailed description is omitted. The microphone 11 is a microphone used in a band from DC to about 30 kHz. The microphone 12 is 20 kHz
The microphone has excellent characteristics in a band of z or more. The microphone 11 has a diaphragm having a relatively large diameter,
The microphone 12 has a relatively small diameter.

FIG. 8 is a diagram for explaining a signal spectrum and a noise spectrum of the ΔΣ modulator. FIG. 8A shows ΔΣ
The output Ya of the modulator 100, FIG.
8C and the output Yb of the ΔΣ modulator 500 are shown in FIG.
The characteristic of c is shown. Note that the horizontal axis is the frequency axis, which is logarithmically shown for viewing a wide range.

In FIG. 8A, S1 is a signal spectrum of the input signal X1, and has a flat spectrum in a low frequency band.

Next, S2 in FIGS. 8B and 8C is a signal component input from the microphone 12, and has a flat characteristic in a high frequency range.

These are added and combined by the combining means 7000 via the Δ し て modulation and the decimation filter as in the first embodiment.

FIG. 9 is a diagram showing the characteristics of each decimation filter in the second embodiment. In the figure, Fa indicates the characteristic of the decimation filter 200,
It is the microphone 1 that drops the gain by about 15 dB.
This is to correct that the output of No. 1 is larger than the output of the microphone 12. Fb indicates the characteristic of the decimation filter 400. To correct the tendency of the microphone 12 to attenuate high frequencies, Fb is corrected by convolving a transfer characteristic having an inverse characteristic. As a result, the overall input / output characteristics are the same as in FIG. Na, Nb and Nc in the figure are residual noises. A dynamic range of 146 dB or more is obtained in a band from DC to 96 kHz. By providing a plurality of input terminals, the microphone can be of a multi-way type, and there is an advantage that correction can be easily performed by making the most of each characteristic and performing optimal equalization characteristics. Note that the same functions and effects as those of the first embodiment are obtained for the basic parts.

[0040]

As described above, according to the present invention, there are provided a microphone for collecting input acoustic energy in a predetermined partial band, and n microphones for converting a digital code in a predetermined partial band (n is an integer of 2 or more). ), And synthesizing means for synthesizing the n outputs of the AD conversion element group, and digital codes of the entire band are taken out from the synthesizing means.

Further, the AD conversion element thins out sampling data by limiting the band of the output of the ΔΣ modulator with a predetermined frequency characteristic, and a ΔΣ modulator for ΔΣ modulating an input analog signal with a predetermined band characteristic. And a decimation filter. The decimation filters mainly pass in a predetermined band of the connected ΔΣ modulator and block in other bands, and each decimation filter synthesizes each output of the AD conversion element. Since the frequency characteristics of the output are configured to be substantially flat in the entire band, each AD conversion element can increase the dynamic range in a predetermined divided band using a relatively low clock and a low-order feedback filter. Stabilization is also achieved. These AD conversion elements are combined with a decimation filter that passes through a predetermined band and blocks out of the band, and removes noise outside a predetermined divided band. Furthermore, by combining the outputs of a plurality of AD conversion elements that obtain predetermined performance in different bands, a wider band and a higher dynamic range can be achieved as a whole. In addition, n ADs
When the outputs of the conversion elements are combined, the rise and fall appearance probabilities of the ΔΣ modulation waveform are substantially balanced, so that an operation of geometrically averaging conversion errors due to jitter occurs, and the effect of reducing noise due to jitter is secondary. Occurs.

That is, the following specific effects are obtained. (A) Since the oversampling ratio can be reduced, the operation speed of the device can be afforded, and an AD converter that is economically excellent with little variation as designed can be obtained. By combining this with a partial microphone, a microphone device with excellent characteristics can be obtained. realizable.

(B) Since the order of the feedback filter can be reduced, an AD converter which always operates stably even at full swing or when there is a DC offset is obtained. By combining this with a partial microphone, A microphone device having excellent characteristics can be realized.

(C) Since the microphone outputs divided into partial bands are added and synthesized via the AD converter and the decimation filter, it is easy to obtain a desired wide bandwidth, and at the same time, a high dynamic range can be obtained.

(D) The function of geometrically averaging the conversion error due to jitter occurs, and the effect of reducing noise due to jitter occurs secondarily.

As described above, the present invention is an excellent microphone device that can stably and economically realize a microphone device suitable for picking up an ultra-wideband audio signal in a high dynamic range, which has been difficult to realize. is there.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram illustrating a microphone device according to a first embodiment of the present invention.

FIG. 2 is an internal block diagram of an AD converter (a) 1000 in the embodiment.

FIG. 3 is a frequency characteristic diagram showing an output characteristic of the ΔΣ modulator in the embodiment.

FIG. 4 is a frequency characteristic diagram showing characteristics and a noise spectrum of the decimation filter in the embodiment.

FIG. 5 is an internal block diagram of a synthesizing unit 7000 in the embodiment.

FIG. 6 is a view showing a total frequency characteristic of an output signal W with respect to an input signal X in the embodiment.

FIG. 7 is a schematic block diagram illustrating a microphone device according to a second embodiment of the present invention.

FIG. 8 is a frequency characteristic diagram showing an output characteristic of the ΔΣ modulator in the embodiment.

FIG. 9 is a diagram showing characteristics of respective decimation filters in the embodiment.

[Explanation of symbols]

 11, 12, 13 Microphone 100, 300, 500 ΔΣ modulator 110 Adder 120 Quantizer 140 Subtractor 150 Feedback filter 200, 400, 600 Decimation filter 210 FIR1 filter 220 FIR2 filter 1000 AD conversion element (a) 2000 AD conversion Element (b) 3000 AD conversion element (c) 7000 Synthesizing means

Claims (9)

[Claims] 1. A microphone comprising i (i is an integer of 2 or more) microphones each having characteristics suitable for a predetermined sub-band, or a microphone amplifier added as needed and a pre-filter added as needed. N (n is an integer of 2 or more) for converting a signal of the microphone amplifier into a digital code in a predetermined partial band.
And a synthesizing means for synthesizing the n outputs of the AD converting element, and a plurality of partial-band microphones configured to extract digital codes of the entire band from the synthesizing means. 2. The apparatus according to claim 1, further comprising: i microphones (i is an integer of 2 or more) each having a characteristic suitable for a predetermined partial band, or a microphone amplifier added as needed and a pre-filter added as needed. N (n is an integer of 2 or more) for converting a signal of the microphone amplifier into a digital code in a predetermined partial band.
And a synthesizing means for synthesizing the n outputs of the AD conversion element group into a digital code of m bits (m is a positive integer satisfying 2 ^m ≧ n + 1). A microphone device comprising a plurality of partial band microphones for extracting digital codes of the entire band. 3. A microphone device comprising a plurality of sub-band microphones according to claim 1, wherein i is equal to n. 4. A microphone device comprising a plurality of partial band microphones according to claim 1, wherein said plurality of AD converters are AD converters each having a predetermined conversion characteristic in a different partial band. . 5. An A / D converter comprising: a ΔΣ modulator for ΔΣ modulating an input analog signal with a predetermined band characteristic;
5. The microphone device comprising a plurality of partial band microphones according to claim 4, further comprising: a decimation filter that limits a band of each output of the modulator with a predetermined frequency characteristic to thin out sampling data. 6. The microphone device comprising a plurality of partial band microphones according to claim 5, wherein the ΔΣ modulator obtains a predetermined band characteristic by a transfer characteristic of a feedback circuit for feeding back quantization noise. 7. The partial band microphone according to claim 5, wherein the decimation filter passes mainly in a predetermined band of each of the Δ す る modulators to be connected, and blocks other bands. Microphone device. 8. The decimation filter according to claim 5, wherein each of the outputs of the AD conversion elements has a predetermined transfer characteristic such that the frequency characteristic of the output obtained by combining the outputs is substantially flat in the entire band. A microphone device comprising a plurality of partial band microphones. 9. A decimation filter mainly passes a predetermined band of a ΔΣ modulator connected thereto and blocks other bands, and furthermore, a frequency characteristic or a phase characteristic between i input signals. Or, adapting to the group delay characteristics and the variation between them,
7. The microphone device comprising a plurality of partial band microphones according to claim 6, wherein transfer characteristics each having an inverse characteristic are convolved.