JPH04132350A - Microphone - Google Patents

Abstract

PURPOSE:To improve S/N by common-mode rejecting voice signals outputted from a second microphone from the signals outputted from a first microphone, and outputting the obtained signals as transmitting signals. CONSTITUTION:Impulsive noise components included in the transmitting voice signals outputted from the first microphone 3 and the impulsive noise components outputted form the second microphone 4 are almost at the same level and phase, because the first microphone 3 and the second microphone 4 are provided almost at the same position towards a switch 6. Thus, the impulsive noise components included in the transmitting voice signals outputted from the first microphone 3 are canceled by the impulsive noise components outputted from the second microphone 4. As the result, the transmitting voice signals whose impulsive noise components are reduced can be outputted. Thus, the S/N can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to improvements in transmitters installed in wired telephones, portable wireless telephones, car telephones, cordless telephones, intercoms, and the like.

(Prior Art) Generally, in a handset, a microphone is attached to an opening provided in the housing of the handset or telephone body, and the level of the signal output from the microphone is adjusted by an amplifier circuit, and then the output signal is The signal is configured to be sent as a transmission signal.

(Problem to be Solved by the Invention) However, in such a configuration, when the transmitting sensitivity is increased, the impulsive noise generated when a switch such as a hold switch is operated is transmitted to the other party at a relatively loud level. There was a very annoying problem. Furthermore, if the transmitting sensitivity is kept low in order to solve this problem, another problem arises in that it becomes difficult for the other party to hear the content of the call when the speaker's voice is low.

Furthermore, in order to make the housing waterproof, especially for mobile radio telephones, etc., a thin film called a sound waterproof membrane is installed between the microphone and the opening of the housing to which the microphone is attached. There is a new one. Since this sound-appropriate waterproof membrane attenuates the sound pressure to some extent, the level of the audio signal transmitted by the speaker becomes even lower. On the other hand, the impact noise that does not pass through the suitable sound waterproof membrane is detected by the microphone without being affected by the suitable sound waterproof membrane, so the S/N of the transmitted audio signal further deteriorates. was there.

Therefore, the present invention focuses on the above-mentioned circumstances, and aims to improve the S/N by reducing the influence of impulsive noise while ensuring sufficient transmitting voice sensitivity, and is particularly suitable for telephones equipped with a sound-appropriate waterproof membrane. The purpose is to provide a transmitter.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides a first microphone for detecting a transmitted voice and outputting a corresponding transmitted voice signal. In addition, it includes a second microphone for detecting noise transmitted through the housing and outputting a signal corresponding to the noise, and a subtraction circuit, and the subtraction circuit allows the audio signal output from the first microphone to be detected. The signal output from the second microphone is subtracted in phase from the second microphone, and the resulting signal is output as a transmission signal.

(Function) As a result, according to the present invention, when impulsive noise occurs, this impulsive noise is detected by the first microphone that detects the transmitted voice, but at the same time, the second microphone that does not detect the transmitted voice It can also be detected by a microphone. Then, they are canceled by being subtracted by a subtraction circuit. In other words, in the subtraction circuit, only the impulsive noise component is removed while leaving the transmitted voice component unchanged. Therefore, only the impulsive noise component included in the transmitted audio signal can be reduced without lowering the level of the transmitted audio signal, thereby increasing the S/N of the transmitted audio signal. , (Example) Next, an example of the present invention will be described.

FIG. 1 shows the structure of the transmitter in this embodiment, and numeral 1 indicates the casing of a handset-shaped portable radio telephone. A speech hole 11 is provided on the speech surface of the housing 1, and a suitable sound waterproof membrane 2 is pasted on the inner surface of the housing including the position where the speech hole 11 is formed. In addition, case 1
A first microphone 3 is attached to the inner surface at a position where the speech hole 11 is formed, with the appropriate sound waterproof membrane 2 interposed therebetween. The first microphone 3 detects the transmitted voice inputted through the voice transmission hole 11 and the appropriate sound waterproof membrane 2, and outputs a transmitted voice signal.

By the way, a second microphone 4 is attached to a position in the housing 1 at a position where the transmission hole 11 is not formed and adjacent to the first microphone 3 with the sound-appropriate waterproof membrane 2 interposed therebetween. has been done. This second microphone 4 has the same audio characteristics as the first microphone 3, and detects impulsive noise generated by the operation of various switches 6 provided in the housing 1. Output the corresponding signal.

Further, the transmitter of this embodiment has a transmitter circuit 5. This transmitting circuit 5 includes, for example, an operational amplifier O as shown in FIG.
P and resistors R1, R2, R3゜R4, which is a subtraction circuit configured to calculate the voltage riv11 of the transmitting audio signal output from the first microphone 3 to the voltage riv11 of the transmitting audio signal output from the second microphone 4. The output voltage V is obtained by subtracting the voltage value v12 of impulsive noise. is output as a transmitting signal. Note that v8 is a bias voltage.

Here, the values of each of the resistors R1, R2, R3, and R4 are set as follows. That is, the gain between each input terminal and the output terminal is Vo /Vz=R2/R1 for input voltage vl+ Vo /V12-R4/ (R3+R4)x (for input voltage V12)
R1+R2)/R1. Also, the condition for the output voltage vo to be canceled for input terminals v1□ and V12 of the same size and in phase is Vo / V z"' Vo / V 12, so R4 (R1 + R2) - R2 (R3 + R4 ) is set as follows.

With this configuration, first, when a call is in progress and the switch 6 is not operated, the speaker's transmitted voice is transmitted by the first microphone 3 through the speaking hole 11 and the appropriate sound waterproof membrane 2, respectively. However, it is not detected by the second microphone 4 that does not face the speaking hole 11 . Therefore, the first microphone 3 outputs a signal corresponding to the transmitted voice, but the second microphone 4 does not output a signal, and as a result, the transmitting circuit 5 outputs a signal corresponding to the transmitted voice. The transmitting audio signal output from 3 is output as is. Therefore, there is no problem in making calls.

Now, in this state, if the speaker operates switch 6,
Assume that this causes impulsive noise.

Then, this impulsive noise is transmitted to the first microphone 3 via the housing 1, and is detected by the first microphone 3 together with the speaker's transmitted voice signal. Then, the first microphone outputs a transmission audio signal containing the impulsive noise component, and inputs it to the transmission circuit 5. However, the impulsive noise is similarly transmitted to the second microphone 4 adjacent to the first microphone 3, and is also detected by this microphone 4. Then, a signal whose main component is the impulsive noise component is outputted from the second microphone 4 and inputted to the transmission circuit 5.

Therefore, the transmitting circuit 5 is connected to the first microphone 3.
An operation for subtracting the noise component outputted from the second microphone 4 from the transmitted voice signal outputted from the second microphone 4 is performed. At this time, the impulsive noise component included in the transmission audio signal output from the first microphone 3 and the impulsive noise component included in the second microphone 4 are different from each other between the first microphone 3 and the second microphone 4. Since the microphone 4 and the microphone 4 are provided at approximately the same position with respect to the switch 6, they are at approximately the same level and in the same phase. Therefore, in the transmission circuit 5, the impulsive noise component included in the transmission audio signal outputted from the first microphone 3 is canceled by the impulsive noise component outputted from the second microphone 4. The result is shocking! A transmitted voice signal with a reduced sound component of 1 is output.

Further, in addition to the case where the switch 6 is operated, the impact noise generated by the telephone is also reduced when the telephone is dropped or brought into contact with a desk or the like during a call.

In this way, in this embodiment, only impulsive noise is detected by the second microphone 4, and using this detection output, the transmission circuit 5 detects the noise included in the transmission audio signal output from the first microphone 3. This cancels the impulsive noise component that is mixed into the transmitted audio signal, so even if impulsive noise occurs due to the operation of the switch 6 or the accidental contact of the phone case during a call, this impulsive noise component mixed into the transmitted voice signal is canceled. can be reduced. Therefore, the problem of sending harsh impulsive noise to the other party is alleviated. In addition, there is no need to set the transmitting sensitivity particularly low, and it can be set freely, so it is possible to set the transmitting sensitivity to any other party! It is possible to prevent problems such as the received voice level becoming low and becoming difficult to hear.

Furthermore, in this embodiment, the second microphone 4 is mounted on the housing 1 with the sound-appropriate waterproof membrane 2 interposed in the same manner as the first microphone 3, so that the detection conditions for impulsive noise are 1 as close as possible to that of microphone 3, thereby making it possible to more reliably cancel impulsive noise components.

Note that the present invention is not limited to the above embodiments. For example, in the embodiment described above, the second microphone 4 was installed adjacent to the first microphone 3, but the second microphone was installed on the opposite side of the switch that generates impulsive noise. The switch may be set at a position where the distance from the switch is the same and the distance from the switch is the same. In this way, the conditions for detecting impulsive noise by the second microphone are set to be approximately equal to the conditions for detecting by the first microphone, and the detection level of the transmitted voice by the second microphone can be made very small. I can do it. Therefore, by minimizing the influence on the transmitted voice, the S of the transmitted voice is
/N can be kept high.

Furthermore, as the second microphone, a microphone whose input sensitivity characteristics are set to be high in the impulsive noise band and low in the transmitted voice band may be used, and furthermore, a microphone whose pass characteristic is set to be high in the impulsive noise band and low in the transmission voice band may be used. A filter may be installed that is set to be high in the transmit voice band and low in the transmit voice band.

By doing the above, it is possible to make the transmitted voice component included in the detection voltage of the second microphone extremely small, thereby minimizing the influence on the transmitted voice and reducing the S/N of the transmitted voice. can be kept high.

Furthermore, when the impulsive noise detection voltage VI2 output from the second microphone and the impulsive noise detection voltage V11 output from the first microphone are subtracted by the transmitting circuit, it is ensured that the impulsive noise detection voltage VI2 becomes zero. Thus, an offset voltage may be superimposed on the detection voltage V12 or Vl+ in advance. In this way, even if the installation position of the second microphone cannot be set so that the detection conditions for impulsive noise are the same as the detection conditions for the first microphone, the impulsive noise contained in the transmitted audio signal can be Noise components can be reliably canceled.

In addition, the installation position of the second microphone, the circuit configuration of the subtraction circuit, the type and configuration of the telephone to which it is applied, etc. can be modified in various ways without departing from the gist of the present invention.

[Effects of the Invention] As detailed above, according to the present invention, the second microphone detects the noise transmitted through the housing, and the subtraction circuit detects the transmitted voice output from the first microphone. By subtracting the in-phase signal output from the second microphone from the signal and outputting the resulting signal as a transmitting signal, sufficient transmitting voice sensitivity is ensured and impulsive noise is eliminated. It is possible to reduce the influence of noise and improve the S/N ratio, and to provide a transmitter that is particularly suitable for a telephone equipped with a soundproof waterproof membrane.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the structure of a transmitter according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing the structure of a transmitter circuit of the same transmitter. DESCRIPTION OF SYMBOLS 1... Housing, 2... Sound-appropriate waterproof membrane, 3... First microphone, 4... Second microphone, 5... Speech circuit, 6... Switch, 11... ...Speaker hole. Applicant's agent Patent attorney Takehiko Suzue Figure 2

Claims (1)

[Claims] a first microphone for detecting a transmitted voice and outputting a corresponding transmitted voice signal; and a second microphone for detecting noise transmitted through the housing and outputting a signal corresponding to the noise.
and a subtraction circuit that performs in-phase subtraction of the signal output from the second microphone from the audio signal output from the first microphone, and outputs the resulting signal as a transmission signal. A transmitter characterized by: