JPS6248844A - Acoustic coupling prevention circuit - Google Patents

Abstract

PURPOSE:To attain natural talking by cancelling an echo signal obtained at a transmission system by feedback with a reception side sound signal delayed according to the set delay time so as to block the acoustic coupling. CONSTITUTION:In a delay time setting circuit 40, an oscillator 42 generates a simulated sound signal SR so as to use a delay time detection circuit 48 to detect a delay time until a received sound from a reception system 20 is fed back as an echo to a transmission system 8 at each installation, the detected delay time is stored in a delay time memory 54 and the result is set to a delay circuit 38. An echo signal cancelling circuit 26 uses a subtraction circuit 28 to subtract a sound signal delayed for a prescribed time by a delay circuit 38 from a soundsignal fed to a comparator 30 of a talking changeover circuit 12 from the transmission system 8 thereby cancelling the echo signal. Thus, malfunction of transmission/reception changeover by the echo is eliminated to reduce displeasent interval at changeover so as to obtain natural talking state.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an acoustic coupling prevention circuit used in a communication device that switches the direction of communication depending on the transmitted voice and the received voice, and particularly relates to an acoustic coupling prevention circuit used in a communication device that switches the communication direction depending on the transmitted voice and the received voice. Related to prevention of acoustic coupling between microphones and speakers in response to reverberation conditions such as.

[Conventional technology]

Conventionally, communication devices compare the levels of the transmitting signal from the microphone and the receiving signal from the telephone line, etc., and switch the direction of the call based on the comparison result, that is, set either the transmitting state or the receiving state. Since audio is input and output using a transmitter with a microphone and a speaker installed in the same housing, measures are taken to prevent malfunctions in switching between transmission and reception due to acoustic coupling between the speaker and microphone. For example, in a handset, the direction of the reproduced sound from the speaker is different from the direction of the sound input from the microphone, or a partition wall is installed between the speaker and the microphone to provide acoustic shielding. In the transmission/reception switching circuit, an acoustic coupling prevention circuit has been proposed that assumes a delay time that can prevent acoustic coupling and sets a certain delay time to prohibit transmission/reception switching within that time. (For example, JP-A No. 60-66560 "Acoustic Coupling Prevention Circuit").

[Problem that the invention seeks to solve]

In acoustic coupling prevention circuits that attempt to prevent malfunctions due to acoustic coupling by setting a fixed delay time, the circuit configuration is complex, and the average delay time required to prevent acoustic coupling is complicated. Therefore, if the reverberation conditions change depending on the location where the handset is installed, the set delay time may not match the reverberation conditions of the installation location.

For example, a long delay time is meaningless in a place where the reverberation time is short, and setting a short delay time will cause a malfunction in a place where the reverberation time is long. This has the disadvantage that there is a delay in switching, making the conversation unnatural.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an acoustic coupling prevention circuit that has a simple configuration and prevents acoustic coupling depending on the installation location of a transmitter/receiver.

[Means for solving problems]

The acoustic coupling prevention circuit of the present invention prevents an audio signal on the transmitting system side (the receiving system 20 in the embodiment) by feeding back the reproduced sound of the audio signal to the microphone (microphone 4 in the embodiment). A delay time setting means (delay time setting circuit 40 of the embodiment) for setting a delay time until a reverberant sound signal is obtained in the transmitting system 8 of the embodiment, and transmitting by feedback of the audio signal from the receiving system. Reverberant sound signal canceling means (reverberating sound signal canceling circuit 26 of the embodiment ).

[For production]

The acoustic coupling prevention circuit of the present invention detects the delay time for each reverberation condition of the installation location, and sets the delay time,
The echo sound signal obtained on the transmitting system side by the feedback of the audio signal from the receiving system side and the audio signal from the receiving side delayed according to the delay time set by the delay time setting means cancel each other out, thereby reducing the echo sound. It cancels the signal and prevents acoustic coupling.

In the acoustic coupling prevention circuit of the present invention, the delay time setting means has a simple configuration, and the simulated sound signal generating means (the oscillator 4 of the embodiment) generates the simulated sound signal.
2) and the delay time of the echo sound signal obtained through the acoustic coupling circuit formed between the speaker and the microphone via the installation location with respect to the simulated sound signal generated by the simulated sound signal generating means. A device location comprising a delay time detection circuit to detect (delay time detection circuit 48 in the embodiment) and a storage means (delay time memory 54 in the embodiment) for storing the delay time detected by this delay time detection circuit. It is possible to detect and set the delay time according to the reverberation conditions.

Further, in the acoustic coupling prevention circuit of the present invention, the echo sound signal canceling means is, for example, a delay circuit (delay circuit 38 in the embodiment) in which a delay time is set by a delay time setting means.
and a subtraction circuit (subtraction circuit 28 in the embodiment) that subtracts the audio signal obtained through the delay circuit from the audio signal on the transmitting side to cancel the echo signal. You can eliminate the signal and avoid its effects.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

The figure shows an embodiment of the acoustic coupling prevention circuit of the present invention.

In the figure, a handset 2 is installed on a tabletop to send and receive calls, and inside the housing of the handset 2 is a microphone 4 that converts the outgoing voice into an electrical signal, and a microphone 4 that converts the outgoing voice into an electrical signal, and a microphone 4 that converts the outgoing voice into an electrical signal. A speaker 6 for converting into audio is provided integrally.

The transmitted voice is converted into a transmitted signal, which is an electrical signal, by the microphone 4, and this transmitted signal is amplified by an amplifier 10 installed at the input stage of the transmitted voice system 8, and then is used as a call switching means. It is applied via circuit 12 to amplifier 14 . The output of the amplifier 14 is sent to, for example, a telephone line 18 via a signal transmission/reception circuit 16.

The signal transmitting/receiving circuit 16 is generally constituted by a hybrid circuit called a speech network, and transmits a transmission signal from the transmission system 8 to, for example, a telephone line 18.
A receiving signal from the telephone line 18 is received and outputted to the receiving system 20.

The receiving signal from the signal transmitting/receiving circuit 16 is transmitted to the receiving system 20.
After being amplified by an amplifier 22 installed in the manual stage, the signal is applied to an amplifier 24 via a call switching circuit 12. amplifier 2
The output of No. 4 is applied to speaker 6, and the received voice is reproduced.

The call switching circuit 12 selectively switches the call direction to the send mode or the receive mode based on the comparison result between the send signal level and the receive signal level. In this embodiment, the transmitting signal obtained from the output side of the amplifier 14 on the transmitting system 8 side is combined with the transmitting signal obtained through the subtraction circuit 28 and diode 29 installed in the echo sound signal canceling circuit 26, and the diode 31. Amplifier 2 of 20 examples of receiving systems obtained through
A comparator 30 compares the receiving signal on the output side of No. 2, and a call switching signal is obtained by the comparison. For example, comparator 30 generates a high potential output when the transmit signal level is greater than the receive signal level, and a low potential output when the receive signal level is greater than the transmit signal level. The output of the comparator 30 is applied to a switching control circuit 32, which generates a transmitting mode signal or a receiving mode signal based on the call switching signal generated by the comparator 30.

The transmitting mode signal is applied to the current control tl amplifier (CCA) 34 inserted in the transmitting line 8 as a control signal for its amplification gain, and the receiving mode signal is applied to the CCA 34 inserted in the receiving line 20. added to. Therefore, the amplification gain of the CCA 34 is controlled by the transmitting mode signal, allowing passage of the transmitting signal in the transmitting mode, and blocking the transmitting signal in the receiving mode. Further, the amplification gain of the CCA 36 is controlled by the reception mode signal, and in the reception mode, the reception signal is allowed to pass through II1, and in the transmission mode, the reception signal is blocked.

Further, the anti-archaic signal canceling circuit 26 causes the sound reproduced by the speaker 6 of the receiving system 20 to be returned to the microphone 4 as a reverberated sound, and cancels the reverberant sound signal from the transmitting system 8 with the receiving signal.
The echo sound signal prevents malfunctions in call switching. In this embodiment, the subtraction circuit 28
The echo sound signal is eliminated by subtracting the audio signal delayed for a predetermined time by the delay circuit 38 from the audio signal applied to the comparator 30 of the call switching circuit 12. This is a delay time variable type delay circuit configured to be settable, and a delay time setting circuit 40 sets a delay time corresponding to the reverberation conditions of the installation location. Therefore, the echo signal canceling circuit 26 eliminates the echo signal from the audio signal from the transmission system 8 using a delay time depending on the installation location, thereby preventing malfunctions in call switching due to the echo signal.

The delay time setting circuit 40 sets a delay time in the delay circuit 38 according to the existing handset 2, the transmitting/receiving system 8.20, and the acoustic coupling circuit at the installation location. This delay time setting circuit 40 is equipped with an oscillator (O3C) 42 as a simulated sound signal generating means for measuring the delay time, and by closing the push button switch 44, the oscillator 42 enters the delay time detection mode. , and oscillates predetermined simulated sound signals S and I. This simulated sound signal S3 is
The signal is applied as a reference comparison signal to the delay time detection circuit 48 via the diode 46, and after being amplified by the amplifier 24 of the receiver system 20, it is reproduced from the speaker 6 as a simulated sound □. This simulated sound VR is reflected on a reverberant member 50 such as a wall surface of the installation location, and then is returned to the microphone 4 as a reverberant sound. The echo sound VE is from microphone 4.
is converted into a reverberant sound signal SE, and this reverberant sound signal S
, are amplified by the amplifier 10 of the transmission line 8 and then applied to the delay time detection circuit 48 via the diode 52 of the delay time setting circuit 40.

In this case, the delay time detection circuit 48 is switched to the delay time detection mode and holds the simulated sound signal SR generated at a specific time, and the echo sound signal SE arrives at the simulated sound signal St+. In other words, the delay time of the echo sound signal SE is detected. This delay time is
This corresponds to the reverberation time of the installation location, and is stored in a delay time memory 54 installed as a delay time storage means.

In this case, if the installation location is changed, or even if the installation location is the same but the reverberation conditions are changed due to the installed objects, the delay time detection mode can be switched to the delay time detection mode and the simulated sound signal SR can be generated. is detected, and the contents of the delay time memory 54 are updated according to the detected delay time.

Therefore, in this acoustic coupling prevention circuit, with a simple configuration, a delay time corresponding to the installation location is detected, the delay time is set in the delay circuit 38, and the receiving signal delayed by the delay circuit 38 is converted into the transmitting signal. By subtracting from , it is possible to prevent malfunctions in transmission/reception switching due to echo sounds, reduce uncomfortable pauses when switching between calls, and obtain a natural conversation state.

In particular, in this "acoustic coupling prevention circuit", since the delay time is detected using the existing transmitter 2, there is no need to use a test transmitter and receiver, and the configuration is simplified and the measurement value and set value are There is no inconsistency, a highly reliable call state is obtained, and the delay time can be detected and set with simple operations.

Although the embodiments have been described using a speakerphone as an example, the present invention can also be applied to a communication device such as an intercom.

〔Effect of the invention〕

As explained above, according to the present invention, with a simple configuration, it is possible to detect a delay time that matches the reverberation conditions of the installation location, set the delay time, and prevent acoustic coupling due to reverberated sounds. In the device, it is possible to prevent malfunctions such as audio clipping when switching modes due to acoustic coupling, and it also eliminates the need for uncomfortable pauses when switching between calls.
A natural call state can be obtained.

[Brief explanation of the drawing]

The figure is a block diagram showing an embodiment of the acoustic coupling prevention circuit of the present invention. 4...Microphone and 1 phone, 6...Speaker, 8...
Transmitting system, 20... Receiving system, 26... Reverberant sound signal canceling circuit as echo signal canceling means, 28... Subtracting circuit, 38... Delay circuit, 40... Delay time setting means 42... an oscillator as a simulated sound signal generating means; 48... a delay time detection circuit;
54... Delay time memory as storage means.

Claims (3)

[Claims] (1) A delay time setting means for setting a delay time for an audio signal on the receiving system side until a reverberant sound signal is obtained on the transmitting system side by the return of the reproduced sound of the audio signal to the microphone; Reverberant sound signal canceling means for canceling a reverberant sound signal obtained on the transmitting system side by feedback of the audio signal from the system side and the audio signal on the receiving side delayed according to the delay time set by the delay time setting means. An acoustic coupling prevention circuit comprising: (2) The delay time setting means has a simple configuration, and
A simulated sound signal generation means for generating a simulated sound signal, and a simulated sound signal generated by the simulated sound signal generation means are passed through an acoustic coupling circuit formed between a speaker and a microphone via an installation location. Claim 1 is characterized in that it is comprised of a delay time detection circuit for detecting the delay time of the obtained echo sound signal, and a storage means for storing the delay time detected by the delay time detection circuit. Acoustic coupling prevention circuit described. (3) The reverberant sound signal canceling means includes a delay circuit whose delay time is set by the delay time setting means, and a reverberant sound signal by subtracting the audio signal obtained through the delay circuit from the audio signal on the transmitting side. 2. The acoustic coupling prevention circuit according to claim 1, further comprising a canceling subtraction circuit.