JPH0529184B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for preventing ringing and surrounding noise, and particularly to a hands-free system in which a microphone and a speaker are simultaneously used as an integrated structure in communication terminal equipment that performs wired and wireless communication. The present invention relates to a method for preventing ringing and ambient noise, which is intended to suppress the generation of ringing and the mixing of ambient noise in a voice terminal device of this type.

[Conventional technology]

Conventionally, in this type of hands-free audio terminal device, there has been a method of comparing the transmitting audio level and the receiving audio level and blocking low-level signals to prevent the occurrence of ringing, or A noise and ambient noise prevention method such as an echo canceller method that predicts the signal level of the signal and subtracts it from the transmitted signal is generally used.

[Problem that the invention seeks to solve]

The conventional ringing prevention method described above is always in a reception-only or transmission-only state, so
The drawback is that simultaneous two-way calls cannot be made.

Furthermore, the echo canceller method has the disadvantage that it is difficult to predict the level of the signal that goes around, and it is inevitable that it cannot be canceled sufficiently.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for preventing noise and ambient noise, which eliminates the above-mentioned drawbacks and can significantly prevent noise and ambient noise with a simple configuration.

[Means for solving problems]

A sound and ambient noise prevention method for hands-free voice terminal equipment that uses a microphone for transmitting communication voice and a speaker for outputting received voice at the same time in communication terminal equipment that performs wired and wireless communications, and is mainly used for transmission. a first microphone that receives sound; a second microphone that obtains a reference signal mainly for suppressing sound and ambient noise; and the midpoint of a line segment connecting the first microphone and the second microphone. and an arithmetic circuit that subtracts a reference signal output from the second microphone from the audio signal received by the first microphone to eliminate ringing and surrounding noise and sends the audio signal to the communication line. The first microphone and the second microphone have the same directivity and have effective sensitivity only near the vertical front, and are arranged side by side at a predetermined interval.

〔Example〕

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. A received signal input from a receiving terminal 101 connected to a wireless or wired communication line is amplified by an amplifier 1, and is sent out into space from a speaker 2 as sound. The first microphone 3 receives various sound waves from the surrounding space, converts them into electrical signals, and outputs the electrical signals. Like the first microphone 3, the second microphone 4 receives various sound waves from the surrounding space, converts them into electrical signals, and outputs them as reference signals.

In FIG. 1, a first microphone 3 and a second
The speaker 2 has the same characteristics as the microphone 4 and has an effective sensitivity in the space in front of the communication distance at most, and the speaker 2 is placed at the midpoint of the line segment connecting the first microphone 3 and the second microphone 4, and These two microphones, the speaker 2, and the arithmetic circuit 5 are all integrated into the body.

Now, S ₁ is the sound that reaches the first microphone 3 from the speaker 2, and S ₂ is the sound that reaches the first microphone 3 from the speaker 2.
It is assumed that the voice reaching the microphone 4 of Further, V ₁ represents the transmission audio signal that has reached the first microphone 3 to be sent to the communication line, V ₂ similarly represents the transmission audio signal that has reached the second microphone 4, and furthermore, N ₁ represents the ambient noise that reaches the first microphone 3, and _N2 represents the noise that reaches the second microphone 4.

The arithmetic circuit 5 performs a calculation to subtract the electrical signal obtained by the second microphone M2, that is, the reference signal, from the electrical signal obtained by the first microphone ₃ , and is connected to a wireless or wired communication line. This is sent to the communication line via the output terminal 501.
First microphone 3 and second microphone 4
The reception sensitivities of the speakers can be made equal, and by selecting an appropriate distance from the speaker 2, the reception strength of the sound arriving from the speaker 2 can also be made equal. Furthermore, for noise whose source is sufficiently far from the two microphones, N ₁ =N ₂ can be set. Therefore, from the output terminal 501, among the transmission audio signals to be communicated, V ₁ captured by these microphones is outputted from the output terminal 501.
Only the signal corresponding to the difference between and V ₂ is sent to the communication line, and the feedback from the reception terminal 101 and noise from the surroundings are eliminated.

FIG. 2 shows the arithmetic circuit 5 in the embodiment of FIG.
This is a circuit diagram showing a first example of resistors R ₁₀ , R ₁₁ ,
It is configured to include R ₂₀ , R ₂₁ and an operational amplifier 51. i ₁ is a received signal from the first microphone 3, and i ₂ is a received signal from the second microphone 4. j is the output of the arithmetic circuit 5 |i ₂ −
i ₁ | Sends the corresponding signal j.

FIG. 3 shows the arithmetic circuit 5 in the embodiment of FIG.
FIG. 5 is a block diagram showing a second embodiment of the coder 5.
2, 53 and a digital subtraction circuit 54. The coder 52 is the first microphone 3
The coder 53 converts the analog signal i from the second microphone ₄ into a digital signal.
Further, the digital subtraction circuit 54 converts the digital signal converted by the coder 53 into the digital signal converted by the coder 53.
In step 2, the digital signal jd obtained by subtracting the converted digital signal is output.

FIG. 4 is a layout diagram for explaining the noise prevention effect of the present invention. Now the first microphone 3
Assuming that the distance between the speaker 2 and the speaker 2 is r ₁ , the energy E ₁ of the sound wave from the speaker 2 at the first microphone 3 can be expressed as follows, with α ₁ being a proportionality constant.

E ₁ = 1/r ₁ ² α _1Similarly , the second microphone 4 and speaker 2
_{The energy E 2 of} the sound wave from the speaker 2 at the second microphone 4 is
It can be expressed as follows, where α ₂ is a constant of proportionality.

E ₂ =1/r ₂ ² α ₂ The value obtained by subtracting E ₂ from E ₁ by the α 2 calculation circuit 5 is as follows.

E ₁ −E ₂ = 1/r ₁ ² α ₁ −1/r ₂ ² α ₂ = r _{2 2} ^α ₁ −r ₁ ² α ₂ /
Wraparound can be eliminated by selecting r ₁ ² r ₂ ² r ₁ , r ₁ , α ₁ , and α ₂ . Here, α ₁ and α ₂ are constants resulting from the characteristics of the first and second microphones 3 and 4 and environmental conditions such as surrounding obstacles.

FIG. 5 is a layout diagram for explaining the reception situation of a transmission audio signal in the present invention, and FIG. 6 is a reception energy characteristic diagram of a microphone.

In FIG. 5, 6 is an audio source with which communication is to be performed, and the distance from the first microphone 3 is x,
Let the distance to the second microphone 4 be x+d.
Here, if the energy of the sound waves from the sound source 6 in the first microphone 3 and the second microphone 4 is P _M1 and P _M2 respectively, the relationship with the distance x is P _M1 > P _M2 as shown in FIG. There is a relationship between
Furthermore, the difference becomes smaller where x is larger.
FIG. 7 is a subtracted reception energy characteristic diagram showing the difference between the two reception energies shown in FIG. As is clear from FIG. 7, the received sound energy obtained by the method of the present invention decreases in inverse proportion to the fourth power of the distance x from the sound source.

FIG. 8 is a reception sensitivity characteristic diagram using a single omnidirectional microphone. Point 0 is the position of a single omnidirectional microphone, and the equisensitivity region forms concentric circles around point 0. Also, the straight line X-Y
The vertical sensitivity distribution between them exhibits a characteristic P∝1/r ² that decreases in inverse proportion to the square of the distance.

FIG. 9 is a reception sensitivity characteristic diagram of the microphone according to the present invention. Comparing this with the characteristics of a single microphone in Figure 8, we can see that two microphones,
In other words, the sensitivity to sound having a sound source located at a location equidistant from the first microphone 3 and the second microphone 4 becomes extremely low. Also, the receiving sensitivity characteristics in the vertical direction between the straight line V and W of the two microphones are attenuated in inverse proportion to the cube of the distance x according to P∝｜2d ₀ x/(x ² - d ₀ /4) ² | However, the range of sound sources that can be received is limited to the vicinity of the first and second microphones 3 and 4.

As described above, the reception sensitivity distribution according to the method of the present invention has a characteristic that the sensitivity decreases rapidly as the distance from the sound source increases compared to a single omnidirectional microphone. It is possible to significantly suppress noise with the sound source position from entering the communication line.

〔Effect of the invention〕

As explained above, the present invention receives audio with two microphones, calculates the difference in their outputs, sends a signal to a communication line, and places a speaker that outputs the receiver at the midpoint between the two microphones. By adopting an integrated hands-free configuration, it is possible to eliminate ringing sounds and noises around the terminal, and to send only voices originating near the microphone to the communication line.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a circuit diagram of a first embodiment of the arithmetic circuit 5 in the embodiment of FIG. 1, and FIG. Block diagram of the second embodiment of the arithmetic circuit 5, No. 4
FIG. 5 is a layout diagram for explaining the noise prevention effect of the present invention, FIG. 5 is a layout diagram for explaining the reception status of the transmission audio signal in the present invention, and FIG. 6 is a reception energy characteristic diagram of the microphone. , FIG. 7 is a subtraction reception energy characteristic diagram showing the difference between the two reception energies in FIG. It is a diagram. 1...Amplifier, 2...Speaker, 3...First
microphone, 4...Second microphone, 5
...Arithmetic circuit, 6...Audio sound source, 51...Operation amplifier, 52, 53...Coder, 54...Digital subtraction circuit.

[Claims]

1: an image data output means for converting handwritten image information into image data of electrical signals; an image data accumulation means for accumulating the output of the image data output means; and an output of the image data output means and the image data accumulation means. In the telewriting device, the above-mentioned telewriting device is equipped with a modulation means for modulating the output and transmitting the modulated image data to the other party's terminal device via the transmission line, and a demodulation means for demodulating the modulated image data input via the transmission line. When displaying each image of the output of the image data output means and the output of the image data storage means, the modulation means modulates the output of the image data output means and the output of the image data storage means to connect the transmission line. 1. A telewriting device comprising: display means for automatically distinguishing and displaying whether or not the transmission has been sent to the other party's terminal device.