JPS62298257A - Loudspeaker telephone system - Google Patents

Abstract

PURPOSE:To surely prevent the malfunction of an acoustic switch by using an echo canceller circuit so as to eliminate an echo component and passing either a reception signal or a transmission signal through the acoustic switch based on the output signal of a comparision means so as to attenuate the other signal. CONSTITUTION:An acoustic coupling component invaded in a transmission detection signal is eliminated by the action of a 1st echo canceller circuit 21 and a 1st adder 24 and a side tone coupling component invaded in a reception detection signal is eliminated by the action of 2nd echo canceller circuit 31 and a 2nd adder 34 and the result is fed to a voice switch control section 40, which compares the level of the reception detection signal and the transmission detection signal so as to adjust the loss of a reception channel insertion/loss section 4 and a transmission channel insertion/loss section 9 in response to the level of both signals thereby forming the reception and transmission state. As a result, the channel switching of transmission/reception is controlled with high accuracy. Further, the malfunction of the voice switch due to echo is prevented.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Object of the Invention] (Field of Industrial Application) The present invention relates to an improvement of a public address telephone device used in a group 11 telephone system and the like.

(Prior art) In recent years, conference telephone systems have become widespread in corporate organizations, and in this case, the telephone set is a public address telephone set in A-1, which allows conference participants to talk using a microphone and speaker without having to have a handset. is convenient and often applied.

FIG. 2 is a block diagram showing the configuration of a conventional loudspeaker telephone device of this type. In the figure, a received signal input from a telephone line 1 is transmitted to a side sound protection circuit 2. Human power of receiver 3. The signal is outputted as audio by the speaker 6 via the receiving channel insertion/loss section 4 and the speaker amplifier 5.

On the other hand, the audio captured by the microphone 7 is converted into a transmission signal and sent to the microphone amplifier 8. Transmission channel insertion/loss section9. Transmission specific power 7 10 and side sound protection circuit 2
is sent to telephone port l111 via.

Here, the channel switching control between the receiving state and the transmitting state is performed by adjusting the signal level of the receiving signal detected by the receiving signal detecting section 11 and the transmitting signal detected by the transmitting signal detecting section 12. Generally, a so-called audio switch is used, which compares the signals by a section 13 and controls the receive channel insertion/loss section 4 and the transmit channel insertion/loss section 9 based on the level difference. Specifically, when the receiving signal level is higher, the loss of the receiving channel insertion/loss section 4 is reduced, and the loss of the transmitting channel insertion/loss section 9 is increased to establish a listening state. By doing this, speaker 6
A reception signal is supplied to the device and the voice is emitted, but
The sound from the speaker 6 input to the microphone 7 is not guided to the line 1, and no howling occurs.

Conversely, when the transmitting signal level is higher, the loss of the transmitting channel insertion/loss section 9 is reduced, and the receiving channel insertion/loss section 9 reduces the loss.
The loss of the loss section 4 is increased to enter the transmitting state.

Further, the received signal detection section 11 and the transmitted signal detection section 1
2, bandpass filters 11a and 12a for improving the S/N ratio of audio signals, time constant units 11b and 12b for detecting the average level of audio signals, and A/D conversion for converting into digital values. The circuits 11c and 12c are used to monitor echo components such as acoustic coupling and sidetone coupling within the communication band. Then, the output of the speaker 6 is input to the microphone 7 during the receiving state, and the audio switch control unit 13 is prevented from malfunctioning due to acoustic coupling mixed into the transmission signal detected by the transmission signal detection unit 12. In the transmitting state, the output of the transmitting output amplifier 10 is input to the receiving human power amplifier 3 via the side sound protection circuit 2,
This prevents the audio switch control section 13 from malfunctioning due to sidetone coupling mixed into the received signal detected by the received signal detection section 11.

However, in the above-mentioned conventional device, if the remaining W time is long in the blank space where the telephone device is installed, the microphone 7
Since the level of the reverberant sound taken in by the speaker 6 becomes high, there is a possibility that the reverberant sound is mistakenly recognized as a transmission signal from the caller, and the audio switch control section 13 malfunctions.

(Problems to be Solved by the Invention) As described above, conventional audio switches may malfunction depending on the installation location, and improvements in this respect have been desired.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a loudspeaker telephone device that can reliably prevent malfunction of an acoustic switch even if it is installed in a room with a long reverberation time.

[Structure of the invention] (Means for solving the problems) In order to solve the above problems and achieve the purpose, the present invention has the following features:
A received signal that is input via a telephone line is detected by a received signal detection section, and a transmitted signal that is input via a microphone is detected by a transmitted signal detection section. The signal levels of the received signal and the transmitted signal are compared by a comparing means, and an echo component provided in at least one of the received signal detection section or the transmitted signal detection section is removed by an echo canceller circuit. Based on the output signal of the circuit and the comparison means, an audio switch is used to pass either the received signal or the transmitted signal and attenuate the other signal.

(Operation) By taking such measures, the signal level of the received signal detection section or the transmitted signal detection section will not become abnormally high due to echo components.

(Embodiment) FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. Note that the same parts as in FIG. 2 are given the same reference numerals, and detailed explanations will be omitted. In FIG. 1, 21 is a first echo canceller circuit composed of an adaptive filter such as an adaptive finite impulse response filter. The input signal of A/D converter 22. The signal is supplied via a band-limiting filter 23. Further, 31 is a second echo canceller circuit also composed of an adaptive filter, and the input terminal of this second echo canceller circuit 31 receives the input signal to the transmitting signal detecting section 12 from the A/D converter 32, It is supplied via the WI band limiting filter 33.

The output terminal of the first echo canceller circuit 21 is the first
The first adder 24 is connected to one input terminal of the adder 24, and the output terminal of the band-limiting filter 33 is connected to the other input terminal of the first adder 24. The output of the first adder 24 is subjected to time constant processing in a time constant section 25, and then sent to the voice switch sub-section 40 as a transmission detection signal.
It is intended to be supplied to

Further, the output terminal of the second echo canceller circuit 31 is connected to one input terminal of a second adder 34, and the other input terminal of the second adder 34 is connected to the band-limiting filter 23. output terminal is connected. Then, the output of the second adder 34 is subjected to time constant processing in a time constant section 35, and is then processed as a reception pressure signal by the voice switch control g.
It is supplied to the IJ section 4'0.

The voice switch control section 40 performs a conventional voice switch control section based on the signal levels of the reception detection signal input through the time constant section 35 and the transmission detection signal input through the time constant section 25. Similarly to No. 13, the state switching control between the receiving channel and the transmitting channel is performed.

Next, the operation of this embodiment will be explained. The reception signal input from telephone line 1 is transmitted to the anti-il! l sound circuit 2゜receiver circuit 3. The signal is outputted as audio by the speaker 6 via the receiving channel insertion/loss section 4 and the speaker amplifier 5. Further, the received signal is taken into the received signal detection section 11 via the receiver receiver 3, and at the same time, the received signal is taken in by the A/D converter 2.2. The signal is supplied to one input terminal of the first echo canceller circuit 21 and the second adder 34 via the band-limiting filter 23 .

On the other hand, the audio captured by the microphone 7 is converted into a transmission signal and sent to the microphone amplifier 8. Transmission channel insertion/loss section9. Transmission output amplifier 1o and side sound protection circuit 2
is sent to telephone line 1 via . Further, at the same time, the transmitting signal is taken in by the transmitting signal detecting section 12 via the microphone amplifier 8, and at the same time, the transmitting signal is input to the transmitting signal detecting section 12 through the microphone amplifier 8. The signal is supplied to one input terminal of the second echo canceller circuit 31 and the first adder 24 via the band-limiting filter 33 .

Here, the band-limiting filters 23 and 33 are provided to improve the S/N ratio in voice detection, and for example, 1k) Iz± for the normal voice band tJ4kfb.
500 ) h narrowband. This set band is a band in which echo components such as acoustic coupling and sidetone coupling are likely to be superimposed.In other words, the received signal or the transmitted signal on which the echo component is superimposed is transmitted to the first and second echo canceller circuits 21.
．． Given to 31.

The first echo canceller circuit 21 includes a first adder 24
The echo path of acoustic coupling is estimated and outputted so that the output of the first echo canceller circuit 21 is minimized, and the output of the first echo canceller circuit 21, the microphone 7, the manochrome amplifier 8.
When the first adder 24 adds the output that has been band-limited by the band-limiting filter 33 via the A/D converter 32, echo components due to acoustic coupling are removed. Therefore, the output of the first adder 24 has a small level when the signal on the band-limiting filter 33 side is a signal due to sound W combination, and is output at a high level when it is a transmitting signal. After being subjected to time constant processing at , it is supplied to the audio switch S++ i11 section 40 as a transmission detection signal.

On the other hand, the second echo canceller circuit 31 estimates and outputs the sidetone coupling echo path so that the output of the second adder 34 is minimized. Output and side sound protection circuit 2. Listener Kaambu 3.
When the output which has been band-limited by the band-limiting filter 23 via the A/D converter 22 is added by the second adder 34, echo components due to sidetone coupling are removed. Therefore, the output of the second adder 34 has a low level when the signal on the band-limiting filter 23 side is a signal due to sidetone coupling, and is output at a high level when it is a received signal, and is outputted to the time constant section 35. After being subjected to time constant processing, the signal is supplied to the voice switch control section 40 as a reception detection signal.

Thus, the voice switch control section 40 compares the signal levels of the reception detection signal and the transmission detection signal given via the time constant sections 25 and 35, and when the level of the reception detection signal is higher, the reception is performed. The loss of the channel insertion/loss section 4 is reduced and the loss of the transmission channel insertion/loss section 9 is increased to establish a receiving state. Conversely, when the level of the transmission detection signal is higher, the transmission channel insertion/loss section is increased. The loss of the loss section 9 is reduced and the loss of the receiving channel insertion/loss section 4 is increased to establish a transmitting state. As a result, channel switching between transmission and reception is controlled with high precision.

Note that the received signal detection unit 11 and the transmitted signal detection unit 12 are for monitoring acoustic coupling and sidetone coupling within the communication band, and the band-limiting filters 11a and 12a in both detection units 11. It has a wider band than the limiting filters 23 and 33.

In this way, according to this embodiment, the acoustic coupling component mixed into the transmission detection signal can be removed by the actions of the first echo canceller circuit 21 and the first adder 24,
The combined sidetone component mixed into the reception detection signal can be removed by the actions of the second echo canceller circuit 31 and the second adder 34. Therefore, even if the reverberation time in the room where the one-talk device is installed is long, the echo component is reliably removed, so it is possible to prevent the audio switch from malfunctioning due to echo. Furthermore, since the signals input to the first and second echo canceller circuits 21.31 are band-limited to, for example, 1/4 of the voice band, the first and second echo canceller circuits 21. Second echo canceller circuit 21.31
The hardware amount can be reduced to 1/4 or less compared to when designing for the entire audio band. Therefore, it can be realized with a simple circuit configuration, and there is no risk that the circuit will become a model of Osu. Also,
It takes several seconds to estimate the echo path in the echo canceller circuit 21.31, but since the control over the transmitting/receiving channel insertion/loss section 4.9 during this time is constant, there is no risk of howling occurring. . Therefore, since this device can be used without being restricted by the installation location, it is suitable as a telephone for a teleconference system.

Note that the present invention is not limited to the above embodiments.

For example, in the embodiment described above, A
/D converter 32. Band-limiting filter 33. Second echo canceller circuit 31. Although a case has been shown in which the second adder 34 and the like are provided to remove sidetone coupled components, these are unnecessary when used in a four-linear audio conference system that does not require the sidetone protection circuit 2. Further, even if the connections between the A/D converter 22 and the band-limiting filter 23 and between the A/D converter 32 and the band-limiting filter 33 are reversed, the same effect can be obtained.

Further, in the above embodiment, the band-limiting filters 23, 33 (7
) The case where the limited band is 1kHz+500)1z is shown, but the present invention is not limited to this, and any band in which echo components are likely to be superimposed may be used. It goes without saying that various other modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to provide a loudspeaker telephone device that can reliably prevent malfunction of the acoustic switch even if it is installed in a room where the reverberation time is long.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is a block diagram showing the configuration of a conventional device. DESCRIPTION OF SYMBOLS 1... Telephone line, 2... Side sound protection circuit, 3... Receiving human power amplifier, 4... Receiving channel insertion/loss section, 5
... Speaker amplifier, 6 ... Speaker, 7 ... Microphone, 8 ... Microphone amplifier, 9 ... Transmission channel insertion/loss section, 10 ... Transmission output amplifier, 11 ... Receiving signal detection section, 12... Sending signal detection section, 21°31... 1st. Second echo canceller circuit, 22°32... A/D converter, 23.33...
Band-limiting filter, 24.34...1st. Second adder, 25°35...Time constant section, 40...Audio switch control section.

Claims (2)

[Claims] (1) An incoming call signal detection section that detects an incoming call signal that is input via a telephone line, and a outgoing call signal detection section that detects a outgoing call signal that is input through a microphone. a comparison means for comparing signal levels of a received signal and a transmitted signal; an echo canceller circuit for removing an echo component provided in at least one of the received signal detection section or the transmitted signal detection section; A loudspeaker telephone device comprising: an audio switch that passes one of a received signal and a transmitted signal and attenuates the other signal based on the output signal of the comparing means. (2) The echo canceller circuit is characterized in that a bandpass filter is interposed between the echo canceller circuit and the detection unit to limit the band to a band in which echo components are likely to be superimposed.
Loudspeaker telephone equipment as described in Section 1.