JPH0723492A - Digital microphone - Google Patents

Abstract

PURPOSE:To eliminate deterioration and to attain the system with high sound quality by providing a microphone receiving a sound wave and transducing directly into a digital audio signal thereby building up the audio system processing a digital input signal and eliminating the need for A/D conversion required for a conventional system. CONSTITUTION:A diaphragm 1 receiving directly a sound wave is used and the diaphragm 1 is used for capacitor electrodes, which are used to form an oscillator 4 employing the capacitor and an FM wave from the oscillator is gated by a period of a sampling frequency and the gated FM wave count and a difference between the count and an FM frequency at no sound being a reference value 8s calculated to obtain digital audio data with a specified quantization bit number. Or the FM wave is mixed with a wave of a predetermined frequency and the difference frequency signal is gated at a period of the sampling frequency to obtain digital audio data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microphone for converting a sound wave in the air into an electric signal of sound, and more particularly to a digital microphone for obtaining a digital sound output.

[0002]

2. Description of the Related Art A conventional microphone uses electromagnetic induction to generate vibration of a diaphragm that receives a sound wave, and changes in pressure of the diaphragm cause changes in pressure of carbon particles and the like to change electrical resistance, and a voltage is applied to this. However, there are those that obtain a change in voltage, those that generate electricity by transmitting the vibration of the diaphragm to the piezoelectric element that generates electricity when strain is applied such as Rochelle salt, and those that change the change in the capacitance of the capacitor into the change in voltage. , In both cases, the output of the microphone was an analog signal.

For this reason, a microphone used in a digital system such as a digital console or a digital recording system first amplifies the microphone output with a low noise amplifier and performs A / D (analog-digital conversion). I was getting a digital signal.

[0004]

This conventional microphone requires the low noise amplifier as described above, and since the output voltage of this microphone is extremely low, the S / N (signal-to-noise ratio) can be reduced to other parts. It is more difficult to obtain better quality than the above, and there is a drawback that the overall S / N is determined in this part. Also, an A / D is required, and various measures are required to use an A / D having a sufficiently large quantization number in order to improve the accuracy even in this part. Getting / D was difficult.

[0005]

The microphone of the present invention produces a digital audio signal without converting the vibration received by the diaphragm by the sound wave into an analog audio signal. An oscillator that changes the vibration to a change in the oscillation frequency (FM wave), a gate circuit that gates the FM signal output from the oscillator at the clock cycle of the sampling frequency of the digital audio signal, and a gate circuit for the gated FM signal. A pulse counting unit that counts the number and a calculation unit that calculates the difference between the reference value of the same frequency as when the FM is not modulated and this counted value are output, and digital data is output according to the cycle of the sampling frequency.

Further, the microphone of the present invention includes an FM oscillator that changes the oscillation frequency of a signal received by a diaphragm by a sound wave (FM wave), and a frequency having a predetermined frequency difference from the output of the FM oscillator when there is no sound wave. , A mixer for inputting the signals generated by these two generators to make a difference, and a gate for the difference signal output by this oscillator at the clock cycle of the sampling frequency of the digital audio signal. A gate circuit for passing the gated difference signal for a clock cycle period, and a clock 1 for the difference signal.
Equipped with a pulse count unit that counts the number of each cycle and an operation unit that performs division to obtain the specified number of quantized bits for this output signal, and outputs digital data according to the cycle of the sampling frequency. To do.

Further, the microphone of the present invention comprises, in addition to the above configuration, a detection means for detecting a silent state, and a correction means for correcting a temporal change of the output frequency of the oscillator based on the detection result, and the built-in oscillator Automatically corrects fluctuations in the oscillation frequency.

[0008]

The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a first embodiment of the present invention.

In the figure, the microphone according to the present invention receives a sound wave and vibrates, a diaphragm 1, a fixed pole 2 paired with the diaphragm as a capacitor, a microphone capsule 3 in which the fixed pole 2 is integrated, and the diaphragm 1. An FM oscillator 4 having a capacitance formed by the fixed pole 2 and a fixed pole 2 as a part or all of the capacitance of the resonance circuit, and a gate circuit 6 that gates and outputs an FM wave at a frequency of a sampling frequency clock 5. Pascal count circuit 7 that counts the FM waves one sample at a time, reference value generation circuit 8 that outputs a value corresponding to the counted value when there is no sound (when the oscillator is not modulated), and this reference value Pulse counting circuit 7
And a calculation circuit 9 for calculating a difference from the value from the calculation circuit 9, and outputs a digital audio signal from the calculation circuit 9.

As described above, the sound pressure caused by the sound wave is taken out as the frequency displacement of the FM signal, and the displacement value is regarded as digital data, that is, the quantized voice data of the voice, and output from the arithmetic circuit 9 without passing the analog voice signal. It becomes possible to obtain a digital audio signal. In the embodiment of the present invention, if the sampling frequency is 48 KHz and the number of quantization bits is 10 bits, the frequency change is about 49 MHz (48 KHz × 2 ¹⁰ ).
At this time, if the oscillation frequency straight line portion of the FM oscillator is used, 10 times the displacement is required, which is 490 MHz. If the quantization bit number is 16 bits, the frequency displacement is 3.14 GHz (4 KHz × 10 ¹⁶ ),
The oscillation frequency is 31.4 GHz, which is 10 times the displacement.

FIG. 2 is a view showing a second embodiment of the present invention, in which a vibrating plate 1 which receives a sound wave and vibrates, a fixed pole 2 which forms a pair with the vibrating plate and a capacitor, and which are integrated. As in the first embodiment, the microphone capsule 3 and the FM oscillator 4 are provided.

In the second embodiment, a generator 10 for generating a reference frequency signal having a frequency that is a predetermined difference from the value output from the FM oscillator when there is no sound is mixed with both the FM wave signal and the reference frequency signal. The mixer 11 that outputs the difference, the gate circuit 12 that gates the difference output by the gate signal 5 of the sampling clock cycle, the pulse count circuit 13 that counts the difference output from the gate circuit 12, and the count circuit 13 A gate rising edge detection circuit 14 that produces a reset signal for giving a count timing for each clock cycle, and a pulse count output from the count circuit 13 are used to set the quantization bit number to a specified value of, for example, 10 bits or 16 bits. An arithmetic unit 15 for performing division such as arithmetic is included, and a digital audio signal is output by this.

When the data from the count circuit 13 exceeds the specified number of bits, the arithmetic unit 15 has a function of performing an operation and storing it in the specified number of bits. Further, by appropriately selecting the oscillation frequency of the reference frequency signal generator 10, the data from the pulse count circuit 13 can be set within the specified number of bits. In this case, the calculator 15 can be omitted.

FIG. 3 is a diagram showing a third embodiment of the present invention, in which the fluctuation of the oscillation frequency of the oscillator is further dealt with in the second embodiment. In the configuration of FIG. 3, a silence detector 16 and a frequency control circuit 17 are added to the configuration of the second embodiment. The silence detector 16 receives the output of the arithmetic unit 16, and if this output has not changed for a certain period of time (for example, 10 seconds), it determines that there is no sound and sends the determination output to the frequency control circuit 17. The frequency control circuit 17 receives the output of the mixer 11, and oscillates in the reference frequency signal generator 10 so that the difference frequency from the mixer 11 becomes a predetermined frequency when receiving the silence determination output from the silence detector 16. Control the frequency that is played. By such control, even if the oscillation frequency of the FM oscillator 4 changes with time, it can be automatically compensated. Further, if the frequency control circuit 17 is artificially operated when there is no sound, the silence detector 16 becomes unnecessary.

[0015]

As described above, according to the present invention, the sampling clock 1 that directly changes the degree of change of the diaphragm that receives a sound wave into an FM signal and then undergoes A / D conversion and the like.
It is possible to obtain a digital voice signal having a specified number of quantization bits for each cycle. Furthermore, it is possible to automatically compensate for fluctuations in the oscillation frequency of the FM signal oscillator due to ambient conditions and changes over time.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a third embodiment of the present invention.

[Explanation of symbols]

 1 Vibration Plate 2 Fixed Pole 3 Micro Capsule 4 FM Oscillator 5 Sampling Clock 6,12 Gate Circuit 7,13 Pulse Count Circuit 8 Reference Value Generation Circuit 9 Operation Circuit 10 Reference Frequency Signal Generator 11 Mixer 14 Gate Rise Detection Circuit 15 Arithmetic circuit 16 Silence detector 17 Frequency control circuit

Claims (4)

[Claims] 1. An oscillator that outputs an FM signal (frequency modulation signal) using a diaphragm that vibrates in response to a sound wave as an electrode of a capacitor and a capacitance of the capacitor as a resonance circuit, and a clock of a sampling frequency of a digital audio signal. Output data from the calculation unit according to the cycle of the sampling frequency, which includes a pulse counting unit that gates the FM signal at a cycle and counts every clock cycle, and a calculation unit that calculates the difference between the counted value and the reference value. A digital microphone that outputs as digital audio data. 2. An oscillator for outputting an FM signal (frequency modulation signal) using a diaphragm that vibrates in response to sound waves as an electrode of a capacitor, and the capacitance of this capacitor as a part or all of a resonance circuit, and an output frequency of the oscillator. And a predetermined frequency, a mixer that outputs the difference between the sampling frequency of the digital audio signal, a gate circuit that gates the difference signal at the clock cycle, and a pulse count that counts the difference signal output from the gate circuit for each clock cycle. And a digital microphone having a section. 3. The digital microphone according to claim 2, further comprising an arithmetic unit that receives the count data from the pulse counting unit and performs division from the data to obtain a specified number of quantization bits. 4. The digital microphone according to claim 2, further comprising a silence detecting means for detecting a silence state, and a correcting means for correcting a temporal change of the output frequency of the oscillator based on the output of the silence detecting means.