JP2014072675A - Sound input device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sound input device capable of obtaining excellent speech quality even in a noisy environment by preventing masking of sound caused by picking up low-frequency vibration.SOLUTION: An output signal S2 of a low-pass filter 1 to which a DC signal S1 having certain impedance is inputted is supplied to one end of a resistor 5, and an electret type condenser microphone 14 operative upon supply of a signal obtained from the other end of the resistor 5 is supplied to a skin vibration detector 2 provided with a sensor to detect the vibration of a body surface. A signal S3 derived by superposing the output signal of the skin vibration detector 2 on the signal obtained from the other end of the resistor 5 is inputted to an impedance conversion element 4. Then, an output signal S4 of a high-pass filter 3 is superposed on the DC signal S1 by the impedance conversion element 4.

Description

  The present invention relates to a voice input device that inputs a voice by detecting a vibration of a vocal cord propagating through a human body tissue and appearing on a skin surface.

  Conventionally, as a means of inputting sound into a wireless or wired broadcast or communication device in a noisy place such as a factory or construction site, the vibration of the vocal cords propagates to the bone tissue, and the vibration transmitted to the bone is transmitted to the skin surface. A bone conduction microphone that picks up sound using a sensor such as a piezoelectric element and an electret condenser microphone that are in close contact with each other is used (for example, see Patent Document 1).

  In a telephone call center or the like, a throat microphone is used to clearly convey an operator's voice. As shown in FIG. 6, the throat microphone brings the sound collection portion 20 a of the microphone 20 into contact with the neck portion 21 under the chin, and the vibration of the vocal cords due to the sound is transmitted to the neck portion 21 under the chin. (See, for example, Patent Document 2).

  In the throat microphone, as shown in FIG. 7, an electret condenser microphone 22 is generally used as a sensor for picking up vibration, and a voice is input to a microphone input unit 23 such as a telephone or a wireless device.

  The vibrating membrane 22a of the electret condenser microphone 22 is housed in the housing 25 together with the impedance conversion element 26, and the skin surface is formed through a sound hole 25a provided at a position corresponding to the vibrating membrane 22a of the housing 25. The vibration is picked up.

  The microphone input unit 23 includes a DC power source 27 for supplying power to the condenser microphone 22, a bias resistor 28 for applying the voltage of the DC power source 27 to the input terminal 24e, and one electrode described above. A capacitor 29 connected to the input terminal 24e and a voltage amplifying element 30 whose input terminal is connected to the other electrode of the capacitor 29 are provided. The negative electrode of the DC power supply 27 is connected to a ground (GND) terminal 24f.

  An output terminal 24c of the impedance conversion element 26, an input terminal 24e of the microphone input section 23, a ground terminal 24d to which the condenser microphone 22 and the impedance conversion element 26 are connected, and a ground terminal 24f on the microphone input section 23 side. For the connection, a two-wire system using a power line 24a sharing a signal line and a power line and a ground line 24b is used. Then, the power line 24a superimposes an audio signal on the power line 24a according to a voltage division ratio based on the impedance of the bias resistor 28 and the impedance of the impedance conversion element 26, and outputs it.

Patent No. 34888749 Japanese Patent Publication No. 8-34643

  However, a frequency characteristic in which a high frequency component attenuates is known as an acoustic characteristic of a signal propagating through a living tissue. For this reason, as shown in FIG. 7, the frequency characteristic of the skin propagation sensitivity when using an electret condenser microphone as a sensor and in close contact with the skin surface is as shown in FIG. 8, for example.

  That is, while a sufficient gain of 100 dB or more can be obtained at a frequency of 100 Hz to 300 Hz, the gain decreases as the frequency increases, and when the frequency exceeds 3 KHz, the gain decreases to 50 dB or less. .

  In such frequency characteristics, in addition to the vibrations that occur when the vocal cords vibrate by generating sound, vibrations with a low frequency of 300 Hz or less that occur when the electret condenser microphone slides on the body surface, or the body is moved. Also, vibrations with a low frequency of 300 Hz or less that occur at the time are picked up, and information on the frequency band of vibrations by voice of 300 Hz or more that is originally required is masked.

  For this reason, when an electret condenser microphone is brought into close contact with the skin surface and vibration is picked up, there is a problem that the sound is not clearly transmitted when used for a voice input device to a communication device or the like.

  In order to solve this problem, it is conceivable to attenuate the low-frequency component of the signal from the sensor that detects the vibration of the skin surface through a high-pass filter, but this method is different from the power supply to the electret condenser microphone. It is necessary to drive the high pass filter with the power supply. For this reason, a power source for a high-pass filter must be prepared separately, and the portability deteriorates when used in a wireless device where portability is important.

  In addition, it is conceivable that a low-frequency component is attenuated in a device such as a wireless device. However, since the low-frequency component of the signal input to the device is attenuated, normal sound caused by air propagation is attenuated. It cannot be shared with the electret condenser microphone for input.

  The present invention has been proposed in view of the above, and an object of the present invention is to attenuate a low frequency component of a signal from a sensor that detects vibration of the skin surface, and to reduce sound generated by low frequency vibration. An object of the present invention is to provide a voice input device which can prevent masking and obtain a good call quality even under noise.

  In order to solve the above-described problem, the audio input device according to the first aspect of the present invention includes a low-pass filter 1 to which a DC signal S1 having a constant impedance is input and an output signal S2 of the low-pass filter 1 at one end. A skin vibration detector 2 provided with a resistor 5 to be supplied, and an electret condenser microphone 14 that operates by being supplied with a signal obtained from the other end of the resistor 5 as a sensor for detecting vibration of the body surface; A signal S3 obtained by superimposing an output signal of the skin vibration detection device 2 on a signal obtained from the other end of the resistor 5 is input, and an output signal obtained by attenuating a low frequency component from the output signal of the skin vibration detection device 2 The high-pass filter 3 for obtaining S4 and the output signal S4 of the high-pass filter 3 are input, and the level of the output signal S4 of the high-pass filter 3 An impedance conversion element 4 whose output impedance changes more, and the direct-current voltage of the direct-current signal S1 is changed between the impedance of the direct-current signal S1 and the impedance of the impedance conversion element 4 that varies depending on the output signal S4 of the high-pass filter 3. The voltage is divided by the ratio, and the output signal S4 of the high-pass filter 3 is superimposed on the DC signal S1.

  According to a second aspect of the present invention, in the voice input device according to the first aspect, the high-pass filter 3 is supplied with the output signal S2 of the low-pass filter 1 as a power source, cuts off a low-frequency component, and removes a high-frequency component. Amplifying.

  The invention according to claim 3 is the voice input device according to claim 1 or 2, wherein the impedance conversion element 4 is a grounded emitter circuit or a grounded source circuit.

  According to a fourth aspect of the present invention, in the audio input device according to any one of the first to third aspects, the low-pass filter 1 includes a first-order low-pass filter, and the high-pass filter 3 includes a first-order high-pass filter. A voice input device characterized by comprising.

  In the voice input device according to the present invention, the output signal of the skin vibration detection device using the electret condenser microphone is input to the high-pass filter to attenuate the low frequency component, so that the sensor is brought into close contact with the skin surface to detect vibration. The acoustic characteristics can be compensated. In this way, by performing the filter processing for attenuating the low frequency, it is possible to prevent voice masking due to low frequency vibration and to obtain a good call quality even under noise.

  Further, by driving the high pass filter using the output of the low pass filter as a power source, it is not necessary to install a power source for driving the high pass filter. Furthermore, since it is not necessary to perform a filtering process for attenuating low-frequency components in a device such as a wireless device, a wireless device connected to the device can be used in the same connection method as a microphone that picks up sound due to air propagation.

It is a principle figure of the audio | voice input apparatus which concerns on embodiment of this invention. It is explanatory drawing which shows an example of the output signal of the skin vibration detection apparatus shown in FIG. FIG. 2 is a frequency characteristic diagram of the high-pass filter shown in FIG. 1. It is a circuit diagram which shows the audio | voice input apparatus based on the Example of this invention. It is explanatory drawing which shows the frequency characteristic of the skin propagation sensitivity in the audio | voice input apparatus which concerns on the Example of this invention. It is explanatory drawing which shows an example of the usage method of a throat microphone. It is a circuit diagram which shows the example of connection to microphone input parts, such as a telephone and a radio | wireless apparatus, of an electret type | mold condenser microphone. It is a figure which shows the frequency characteristic of the skin propagation sensitivity in the case of using an electret type | mold condenser microphone as a sensor and making it contact | adhere to the skin surface.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  First, the principle of the voice input device according to this embodiment will be described with reference to FIGS. 1 to 3, and specific examples will be described with reference to FIGS.

  As shown in FIG. 1, the voice input device includes a low-pass filter (LPF) 1, a skin vibration detection device 2, a high-pass filter (HPF) 3, an impedance conversion element 4, a bias resistor 5, and the like. In the skin vibration detection device 2, an electret condenser microphone 14 is used as a sensor for detecting the vibration of the skin surface. Similar to FIG. 7, this voice input device is configured to input a voice by connecting a microphone input unit such as a telephone or a radio device to the first and second terminals 15 and 16.

  In the above configuration, a DC signal S1 having a constant (several hundred Ω to several kΩ) impedance is input to the low-pass filter 1 to obtain an output signal (DC signal) S2 having a low impedance. This DC signal S2 is supplied to the electret condenser microphone 14 incorporated in the skin vibration detection device 2 via the bias resistor 5. As a result, power is supplied to the condenser microphone 14 to operate. Then, an output signal is obtained by picking up vibrations on the skin surface.

  The output signal of the electret condenser microphone 14 is superimposed on the DC signal by the biasing resistor 5 as shown in FIG. By inputting this output signal S3 to the high-pass filter 3 having the characteristics as shown in FIG. 3, an output signal S4 having a low-frequency component attenuated is obtained.

  By inputting the output signal S4 thus obtained to the impedance conversion element 4, the output impedance of the impedance conversion element 4 changes in conjunction with the output signal S4 and is supplied to the output terminal of the impedance conversion element 4. The direct current signal S1 is divided by the ratio between the impedance of the direct current signal S1 and the output impedance of the impedance conversion element 4. Thereby, as shown in FIG. 2, the audio signal component of the output signal S4 can be superimposed on the DC signal S1.

  Next, the circuit of the embodiment embodied based on the principle diagram of FIG. 1 will be described with reference to FIG. In this embodiment, the low-pass filter 1 is composed of a resistor 6 and a capacitor 10, and the high-pass filter 3 is composed of resistors 7 and 8, a capacitor 11 and a transistor (NPN type bipolar transistor) 12. Therefore, both the low-pass filter 1 and the high-pass filter 3 have a primary filter configuration. The impedance conversion element 4 includes a resistor 9 and a transistor (NPN type bipolar transistor) 13.

  That is, one end of the resistor 6 and the collector of the transistor 13 are connected to the first terminal 15 to which the DC signal S1 is supplied. One end of resistors 5 and 7 and one electrode of capacitor 10 are connected to the other end of resistor 6. A second terminal (GND) 16 is connected to the other electrode of the capacitor 10.

  The other end of the resistor 5 is connected to one end of an electret condenser microphone 14 built in the skin vibration detection device 2 and one electrode of the capacitor 11. The second terminal 16 is connected to the other end of the condenser microphone 14.

  One end of the resistor 8 and the base of the transistor 12 are connected to the other electrode of the capacitor 11. The collector of the transistor 12 is connected to the other ends of the resistors 7 and 8 and the base of the transistor 13, and the emitter is connected to the second terminal 16.

  Further, the emitter of the transistor 13 is connected to one end of the resistor 9, and the other end of the resistor 9 is connected to the second terminal 16. Here, a grounded emitter circuit using a bipolar transistor as an example is shown, but a field effect transistor can also be used. In this case, a grounded source circuit may be used.

  Next, the operation of the embodiment circuit shown in FIG. 4 in the above configuration will be described.

  When a DC signal S1 having a constant impedance is input to a low-pass filter 1 composed of a resistor 6 and a capacitor 10, a DC signal S2 having a reduced impedance is obtained. A signal obtained by inputting the DC signal S2 to one end of the resistor 5 is supplied to the electret condenser microphone 14 built in the skin vibration detection device 2, and the skin vibration detection device 2 is operated.

  The output signal of the skin vibration detection device 2 is superimposed on a DC voltage and output as an output signal S3. In order to attenuate the low-frequency component from the output signal S3, it is input to the high-pass filter 3 composed of the resistors 7, 8, the capacitor 11 and the transistor 12, and the obtained output signal S4 is input to the base of the transistor 13. Thus, the collector current of the transistor 13 changes in conjunction with the output signal S4.

  When the output signal S4 increases, the collector current of 13 increases, so that the impedance from the collector (first terminal 15) to the ground (second terminal 16) of the transistor 13 decreases. Further, when the output signal S4 becomes small, the collector current of the transistor 13 decreases, so that the impedance from the collector of the transistor 13 to the ground increases.

  In this way, by applying the DC signal S1 having a constant impedance to the collector of the transistor 13, the DC voltage of the signal S1 can be obtained by the above-described operation by the ratio of the impedance of the signal S1 to the impedance of the transistor 13 from the collector to the ground. The pressure will be divided.

  Further, since the impedance from the collector of the transistor 13 to the ground changes in conjunction with the output signal S4, the DC voltage of the signal S1 is divided in conjunction with the signal S4, and is detected as vibration of the skin surface. The audio signal is output by being superimposed on the signal S1.

  FIG. 5 is a diagram illustrating frequency characteristics of an output signal in the voice input device according to the embodiment of the present invention. A broken line f1 represents a frequency characteristic of skin propagation sensitivity obtained from an electret condenser microphone, and a solid line f2 represents a frequency characteristic of skin propagation sensitivity in this embodiment. Here, the horizontal axis represents frequency and the vertical axis represents gain. When the broken line f1 and the solid line f2 are compared, it can be confirmed that the low frequency component unnecessary for voice input is attenuated and the high frequency component is amplified in this embodiment.

  As mentioned above, the voice input sound that is generated from the vocal cords is transmitted to the skin surface and picked up by the electret condenser microphone. Without adding a low frequency component, the low frequency component is attenuated and low frequency noise generated during use can be reduced, so that clear voice can be obtained, and good call quality can be obtained even under noise.

  The present invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from the scope of the invention. For example, the low-pass filter, the high-pass filter, the impedance conversion element, and the like are not limited to the configuration example shown in FIG. 4 and can be applied to various configurations.

DESCRIPTION OF SYMBOLS 1 Low pass filter 2 Skin vibration detection apparatus 3 High pass filter 4 Impedance conversion elements 5-9, 28 Resistor 10, 11, 29 Capacitor 12, 13 Transistor 14, 22 Electret type condenser microphone 15 1st terminal 16 2nd terminal 20 Throat microphone 20a Sound collection part 21 Neck part 22a Vibration film 23 Microphone input part 24a Power line 24b Ground line 24c Output terminal 24d, 24f Ground terminal 24e Input terminal 25 Case 25a Sound hole 26 Impedance conversion element 27 DC power supply 30 Voltage amplification element S1 DC Signal S2 Output signal (DC signal)
S3, S4 output signal

Claims (4)

A low-pass filter (1) to which a DC signal (S1) having a constant impedance is input;
A resistor (5) to which an output signal (S2) of the low-pass filter (1) is supplied to one end;
A skin vibration detection device (2) provided with an electret condenser microphone (14) that operates by being supplied with a signal obtained from the other end of the resistor (5) as a sensor for detecting vibration of the body surface;
A signal (S3) obtained by superimposing an output signal of the skin vibration detection device (2) on a signal obtained from the other end of the resistor (5) is input, and an output signal of the skin vibration detection device (2) is obtained. A high-pass filter (3) for obtaining an output signal (S4) in which a low-frequency component is attenuated;
An output signal (S4) of the high-pass filter (3) is input, and an impedance conversion element (4) whose output impedance changes according to the level of the output signal (S4) of the high-pass filter (3),
The DC voltage of the DC signal (S1) is divided by the ratio between the impedance of the DC signal (S1) and the impedance of the impedance conversion element (4) that varies depending on the output signal (S4) of the high-pass filter (3). An audio input device, wherein the output signal (S4) of the high-pass filter (3) is superimposed on the DC signal (S1).   2. The voice input device according to claim 1, wherein the high-pass filter (3) is supplied with the output signal (S2) of the low-pass filter (1) as a power source, cuts off a low-frequency component, and amplifies a high-frequency component. A voice input device.   The voice input device according to claim 1 or 2, wherein the impedance conversion element (4) is a grounded emitter circuit or a grounded source circuit. The audio input device according to any one of claims 1 to 3, wherein the low-pass filter (1) is configured by a first-order low-pass filter, and the high-pass filter (3) is configured by a first-order high-pass filter. A voice input device characterized by that.

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