JPH0194755A - Voice switching circuit - Google Patents

Abstract

PURPOSE:To improve a simultaneous callability by estimating a general intensity (alpha) of an acoustic system echo path between a reception attenuator output and a transmission attenuator input and a line system coupling intensity (beta) between a transmission attenuator output and a reception attenuator input, calculating the attenuating quantities of attenuators, and setting a reception threshold and a transmission threshold. CONSTITUTION:Based on a reception amplitude ratio from a reception amplitude ratio calculating part 9 to subtract a transmission input signal amplitude with a reception output signal, the (alpha) between the output of a reception attenuator 2 and the input of a transmission attenuator 7 is estimated by an (alpha) estimating part 9, and the (beta) is estimated by a (beta) estimating part 12 in the same way. Based on such estimates (alpha) and (beta), the reception threshold and transmission threshold are set by a threshold setting part 14, and a small attenuating quantity is calculating in a range in which howling is not generated by an attenuating quantity setting part 13. Through a transmission/reception deciding part 15, the attenuating quantities of the transmission attenuator 7 and reception attenuator 2 are controlled at the time of receiving and transmitting, respectively. By such constitution, even when the (alpha) and (beta) are changed according to the change of the position of a microphone and a loudspeaker, the reverberation characteristic of a room, etc., the simultaneous callability can be improved without a reception blocking, a transmission blocking, a work head cut, and the howling, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a voice switch circuit for preventing feedback, which is used in two-way communication devices such as loudspeaker telephones and teleconference systems.

2. Description of the Related Art In recent years, loudspeaker systems, %, and reference conference systems have become widespread, and voice switch circuits are used in these devices to prevent howling.

Hereinafter, a conventional audio switch circuit will be explained with reference to the drawings.

FIG. 5 shows a block diagram of a conventional audio switch circuit.

In FIG. 5, 501 is an input terminal into which a reception input signal is input from the line, 502 is a reception attenuator that attenuates the reception input signal and outputs it as a reception output signal to the speaker amplifier 503, 504 is a speaker, and 5051d microphone; 6o6 is a microphone amplifier, 507 is a microphone amplifier 506
508 is an output terminal that outputs the transmitting output signal to the line. 509 is the amplitude of the transmitting input signal. 510 is a receiving amplitude ratio calculation unit that calculates a receiving amplitude ratio by dividing the amplitude of the receiving output signal by the amplitude of the transmitting output signal; Reference numeral 511 is a transmission/reception determination unit that compares the reception amplitude ratio and the transmission amplitude ratio with a preset reception threshold and a transmission threshold to determine transmission/reception. When the judgment signal of the transmitting/receiving determination unit 611 is in the receiving state, no attenuation is inserted into the receiving attenuator 502, and an attenuation amount is set only in the transmitting attenuator 507; No attenuation is inserted in the receiver 607, and an attenuation amount is set only in the receiver attenuator 502.

The operation of the conventional audio switch circuit configured as described above will be described below.

FIG. 6 shows signal waveforms at various parts of the conventional example shown in FIG. 6, and the operation of FIG. 5 will be explained using this diagram.

In FIG. 6, 601 is the waveform of the receiving input signal at point A in FIG. 5, 602 is the waveform of the receiving output signal at point B in FIG.
603 is the waveform of the transmitting input signal at point 0, 604 is the waveform of the transmitting output signal at point D, 605 is the value of the receiving amplitude ratio at point E, and 6
06 is the value of the transmission amplitude ratio at point F, 607 is the transmission/reception determination unit 61
1, 608 is the level of the transmitting threshold set in the transmitting/receiving determination unit 511, 609 is the waveform of the transmitting/receiving determination signal at point G, and 610 is the receiving/receiving attenuation 11502. Attenuation amount setting state 611 indicates the attenuation amount setting state of the transmitting attenuator 507.

In a two-way call, the local end is called the near end, and the other end is called the far end. The speaker on your side is called the near-end speaker, and the speaker on the other side is called the far-end speaker. This term will be used in the following explanation.

The receive input signal 60 of FIG. 6 is the far-end speaker's voice signal.
1 passes through the receive attenuator 502 in FIG.
02, which is amplified by the speaker amplifier 503 and amplified by the speaker 504. Microphone 505 collects the echoed sound from speaker 504 and the voice of the near-end speaker speaking into microphone 505. The output is amplified by a microphone amplifier 506 and becomes a transmitting input signal 603.

This transmitting input signal 603 passes through a transmitting attenuator 507 and becomes a transmitting output signal 604, which is output from an output terminal 608. A receiving amplitude ratio calculation unit 509 divides the amplitude value of the transmitting input signal 603 by the amplitude value of the receiving output signal 602 to obtain a receiving amplitude ratio 606. The transmitting amplitude ratio calculation unit 610 divides the amplitude value of the receiving input signal 601 by the amplitude value of the transmitting output signal 604 to obtain a transmitting amplitude ratio 606.

In the receiving state, the transmitting/receiving determination unit 611 compares the receiving amplitude ratio 605 with the receiving threshold 607, and determines that if the receiving amplitude ratio 606 is greater than or equal to the receiving threshold 607, it is transmitting, and if it is less than that, it is receiving. In the transmitting state, the transmitting amplitude ratio 606 and the transmitting threshold 608 are compared, and when the transmitting amplitude ratio 606 is greater than or equal to the transmitting threshold 608, it is determined that the voice is being received, and when it is below, it is determined that the voice is transmitting. A transmission/reception determination signal 609 that is the determination result is sent to a receiving attenuator 602 and a transmitting attenuator 607 . The amounts of attenuation of these two attenuators are controlled reciprocally by the transmission/reception determination signal 609, and when attenuation is inserted into one, no attenuation is necessarily inserted into the other. That is, in the receiving state, the receiving attenuator 502
The attenuation amount of the transmission attenuator 507 is set to 0, and the attenuation amount of the transmitting attenuator 507 is set to be large. Conversely, in the transmitting state, the attenuation amount of the receiving attenuator 502 is large, and the attenuation amount of the transmitting attenuator 607 is set to zero. As described above, the attenuation amount of the reception attenuator 502 is 61
0, the attenuation amount of the transmit attenuator 605 is controlled as shown at 611.

In this way, the signal amplitude of the receiving system and the signal amplitude of the transmitting system are compared, and the one with the larger amplitude is outputted without attenuation, and the one with the smaller amplitude is outputted with attenuation. That is, the voice of the near-end speaker and the far-end speaker who is speaking in a louder voice is given priority and output. Therefore, it is possible to lower the loop gain, and it is possible to talk at a high volume without causing howling.

Problems to be Solved by the Invention However, the above-described configuration has a problem in that malfunctions such as reception blocking, transmission blocking, and disconnection at the beginning of speech are likely to occur.

Coupling strength of the echo path of the acoustic system formed between the output end of the receiving attenuator 502 and the input end of the transmitting attenuator 607: d
If is too large, that is, if the acoustic coupling between the microphone and the speaker becomes strong, high-level reverberant sound from the speaker 604 will be incident on the microphone 606. As a result, even though the far-end speaker is speaking, the value of the receive amplitude ratio is extremely large and exceeds the receive threshold.
It is erroneously determined that the near-end speaker has started speaking, and the received output signal is attenuated. As a result, the far-end speaker's voice is cut off, resulting in an extremely unnatural call. This phenomenon is call blocking. In order to prevent this, the receiving threshold may be set high in advance, but if it is set higher than necessary, the sensitivity to the near-end speaker's voice will decrease, the beginning of the conversation will be cut off, and the quality of the call will deteriorate significantly.

Also, from the output end of the transmitting attenuator 602 to the receiving attenuator 507
If the coupling strength of the echo path of the line system formed between the line and the input end: β becomes too large, a high-level echo signal of the transmitting output signal will return to the receiver through the line. As a result, even though the near-end speaker is speaking, if the value of the transmitting amplitude ratio is extremely large, it exceeds the transmitting threshold, and it is incorrectly determined that the far-end speaker has started speaking. This will attenuate the transmitting signal. Therefore, the near-end speaker's voice is cut off,
The call becomes extremely unnatural. This phenomenon is call blocking. In order to prevent this, it is sufficient to set the transmission threshold value high in advance, but if it is set higher than necessary, the sensitivity to the far-end speaker's voice will decrease, the beginning of the conversation will be cut off, and the quality of the call will deteriorate significantly.

In order to solve this problem, it is possible to set a threshold value according to α and β, which are the coupling strengths of the echo path, but conventional configurations do not have the function to accurately estimate the values of α and β. .

Furthermore, even if the values of α and β can be estimated, there is no established method for setting the optimal threshold from these values, and with conventional configurations, it is impossible to control the threshold by following the coupling strength. Ta.

Furthermore, in the above configuration, when a near-end speaker and a far-end speaker speak at the same time, the voice of the quieter speaker is excessively attenuated, and no audio information from this speaker is transmitted to the other party. The problem was that it was not communicated.

In order to improve this, the attenuation amounts of the receiving attenuator 602 and the transmitting attenuator 507 may be set to the smallest possible value within a range that does not cause howling.

That is, when the coupling strength (α, β) of the echo path is small, the attenuation amount can be reduced to improve the simultaneous communication performance.

However, if the attenuation amount is set assuming that the coupling strength of the echo path is small, howling will occur when the speaker or microphone moves and the coupling strength increases. Therefore, in the conventional configuration, the amount of attenuation must be set large to prevent howling even when the coupling strength is at its maximum, resulting in poor simultaneous communication performance.

In view of the above-mentioned problems, the present invention makes it possible to control the threshold value and the amount of attenuation in accordance with the magnitude of the coupling strength of the echo path of the acoustic system: α and the coupling strength of the echo path of the line system: β. Reverberation characteristics of 9 rooms with speaker locations 9 Even if σ and β change due to changes in the characteristics of the 9 lines and the characteristics of the communication equipment at the far end, reception blocking occurs.

Does not cause blocking, cut-off, or howling.
The present invention provides a voice switch circuit with excellent simultaneous conversation performance.

Means for Solving the Problem In order to achieve this object, the voice switch circuit of the present invention attenuates the receiving input signal in the transmitting state, and outputs the receiving signal as it is as the receiving output signal without attenuating it in the receiving state. an attenuator, a transmitting attenuator that attenuates the transmitting input signal in the receiving state and outputting it as the transmitting output signal without attenuation in the transmitting state; A receiving amplitude ratio calculator calculates the received receiving amplitude ratio divided by : a d estimating unit that estimates d; a transmitting amplitude ratio calculation unit that calculates a transmitting amplitude ratio by dividing the amplitude of the receiving input signal by the amplitude of the transmitting output signal; and a transmitting attenuator from the value of the transmitting amplitude. The coupling strength of the echo path of the line system formed between the output end of An attenuation amount setting unit that calculates the attenuation amount of the transmitting attenuator, a threshold setting unit that sets the receiving threshold and the transmitting threshold from the estimated value of α and the estimated value of β, and the threshold setting unit that monitors the receiving amplitude ratio in the receiving state. If the receiving amplitude ratio is less than or equal to the receiving threshold, the receiving state is maintained, and if it is above, the transmitting state is entered. In the transmitting state, the transmitting amplitude ratio is monitored, and the transmitting amplitude ratio is set to the transmitting threshold. In the following cases, the transmitting state is maintained, and in the above cases, the transmitting/receiving state is maintained, and in the above cases, the transmitting/receiving state is changed to the receiving/receiving state.

Effect: With this configuration, α and β are calculated by the d estimator and the β estimator.
can now be accurately estimated, and the threshold value setting unit sets an optimal reception threshold and an optimal transmission threshold that prevent reception blocking, transmission blocking, and cut-off at the beginning of speech from occurring, based on the estimated value of α and the estimated value of β. The attenuation amount setting unit sets the attenuation amount of the receiving attenuator and the transmitting attenuator to the smallest possible value based on β and within a range that does not cause howling.

Therefore, the reverberation characteristics of the nine rooms where the microphone and speaker are located, the characteristics of one line, and the characteristics of the communication equipment on the far end side change, and σ
Even if and β change, it is possible to provide a voice switch circuit that does not cause reception blocking, transmission blocking, cutoff at the beginning of a conversation, or howling, and has excellent simultaneous conversation performance.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes an input terminal into which a reception input signal is input from the line, 2 a reception attenuator that attenuates the reception input signal and outputs it as a reception output signal to a speaker amplifier 3, and 4.
is the speaker, 6 is the microphone, 6 is the microphone amplifier, 7
is a transmitting attenuator that attenuates the transmitting input signal that is the output of the microphone amplifier 6 and outputs it as a transmitting output signal to the output terminal 8; 8 is an output terminal that outputs the transmitting output signal to the line; 9 is a transmitting voice A receiving amplitude ratio calculation unit that calculates a receiving amplitude ratio by dividing the amplitude of the input signal by the amplitude of the receiving output signal, and 1o is from the output end of the receiving attenuator 2 to the input end of the transmitting attenuator from the value of the receiving amplitude ratio. The coupling strength of the echo path of the acoustic system formed between:
11 is a transmitting amplitude ratio calculation unit which calculates a transmitting amplitude ratio by dividing the amplitude of the receiving input signal by the amplitude of the transmitting output signal; A β estimator estimates β: the coupling strength of the echo path of the line system formed between the output end of the speech attenuator 7 and the input end of the receiver attenuator 2; 13 indicates the estimated value of a and the estimated value of β; an attenuation amount setting unit 1 that calculates the attenuation amount of the receiving attenuator 2 and the transmitting attenuator 7 from the values;
4 is a threshold setting unit that sets a reception threshold and a transmission threshold from the estimated value of a and the estimated value of β; 16 is a threshold setting unit that sets the reception amplitude ratio, the reception threshold, the transmission amplitude ratio, and the transmission threshold; This is a transmitting/receiving determination unit that determines whether the state should be transmitting or receiving.

The transmitting/receiving determination unit 16 monitors the receiving amplitude ratio in the receiving state, and when the receiving amplitude ratio is less than or equal to the receiving threshold, the receiving state is maintained, and when it is above, the transmitting state is entered. The transmitting amplitude ratio is monitored, and if the transmitting amplitude ratio is less than or equal to the transmitting threshold, the transmitting state is maintained, and if it is above, the transmitting state is maintained, and if it is above, the transmitting state is changed to the receiving state. Controls the transmit attenuator. When the determination signal of the transmitting/receiving determination unit 16 is in the receiving state, no attenuation is inserted into the receiving attenuator 2, and an attenuation amount is set only in the transmitting attenuator 7; conversely, when it is in the transmitting state, the transmitting attenuator No attenuation is inserted in the receiver 7, and an attenuation amount is set only in the receiver attenuator 2.

The operation of the audio switch circuit of the embodiment configured as described above will be explained below.

Prior to explaining the operation of the embodiment shown in FIG. 1, the basic principle of the switching operation of this audio switch circuit will be briefly explained using the analytical model shown in FIG.

In FIG. 2, the far-end speaker is speaking at an amplitude level of vl, and the near-end speaker is speaking at an amplitude level of v8. At this time, the receiving input signal is R1
, the receiving output signal has an amplitude of Ro, the transmitting input signal has an amplitude of Si2, the transmitting output signal has an amplitude of So, the gain of the receiving attenuator is G2, and the gain of the transmitting attenuator is G.

is set to In this voice switch circuit, G,=1. G,=G, in the transmitting state, G,=G.

G8=1. Here, G is set to 1, and Hl in the following equation (@) is set to be positive to prevent howling. In this model, the following relational expression holds.

- Loop gain: M and howling margin: Hm can be expressed by the following equations.

The amplitude ratio (V, /V,) between the near-end speaker's voice and the far-end speaker's voice is called the speech amplitude ratio, and is denoted by K. The receiving amplitude ratio: S, /R0 is determined by the following equation.

FIG. 3 illustrates this equation (3).

The operation of the audio switch circuit will be briefly explained with reference to FIG. Note that this figure is designed for positive hysteresis operation.

Assume now that only the far end speaker is speaking and is in the listening state, and the voice switch circuit is monitoring the value of the listening amplitude ratio: S, /R0. When only the far end speaker is speaking,
The value of the calling amplitude ratio is extremely small, and the receiving amplitude ratio is S.
The value of /R0 is the minimum value. This minimum value is the value of α. At this time, the value of the reception amplitude ratio becomes equal to or less than the reception threshold value 2T, and the reception state is maintained.

Next, it is assumed that there is an interruption by a near-end speaker, that is, a transmission interruption, so that the speech amplitude ratio 2K is greater than or equal to 2A. At this time, the value of the reception amplitude ratio is the set reception threshold:
exceed T. Based on this fact, the voice switch circuit determines that the transmitting side interruption has occurred, and changes to the transmitting state.

After transitioning to the transmitting state, the value of the transmitting amplitude ratio: R1/S0 is monitored, and the transmitting state is maintained until the transmitting amplitude ratio exceeds the set transmitting threshold: T. In the design example shown in Fig. 3, the transmitting amplitude ratio at point K1, where the state transitions from receiving to transmitting state: R1
The value of /S0 is designed to be less than or equal to the transmitting threshold value TI, and the transmitting state is determined at the same time as the transmitting state is entered. In other words, it is designed to have positive hysteresis.

In the sending state, a reception/reception interruption occurs so that the calling amplitude ratio is equal to or greater than 8, and the sending amplitude ratio is set to the sending threshold:
When it exceeds T, the state changes to the receiving state again.

Since it is designed to have positive hysteresis, the receiving state is established at the same time as the receiving state is changed.

The above is the basic principle of the switching operation of the audio switch circuit of the embodiment shown in FIG.

Next, the operation shown in FIG. 1 will be explained in detail with reference to the waveforms of each part.

FIG. 4 shows signal waveforms at various parts of the embodiment shown in FIG. 1, and the operation of the embodiment shown in FIG. 1 will be explained using this diagram.

In FIG. 4, 401 is the waveform of the receiving input signal at point A in FIG. 1, 402 is the waveform of the receiving output signal at 8 points in FIG.
403 is the waveform of the transmitting input signal at point 0, 404 is the waveform of the transmitting output signal at point D, and 405 is the receiving amplitude ratio at point E: S,
/R0 waveform, 406 is the estimated value of the coupling strength of the echo path of the acoustic system at point F: α, and 407 is the transmission amplitude ratio at point G: R, /S
0 waveform, 408 is the coupling strength of the echo path of the line system at point H:
The estimated value of β, 409 is the receiving threshold of 1 point: the level of Tr,
410 is the level of the transmitting threshold: T at one point, 411 is the waveform of the transmitting/receiving judgment signal at the point, 412 is the setting state of the attenuation amount 20 of the receiving attenuator 2, and 413 is the attenuation of the transmitting attenuator 7. i:G
This shows the setting status of .

A voice signal 401 of the far end speaker passes through the receive attenuator 2 shown in FIG.

The microphone 6 collects the echoed sound from the speaker 4 and the voice of the near-end speaker speaking into the microphone 5. The output is amplified by the microphone amplifier 6 and becomes a transmission input signal 403. This transmitting input signal passes through the transmitting attenuator 7 and becomes a transmitting output signal 404, which is output from the output terminal 8. The receiving amplitude ratio calculation unit 9 divides the amplitude value of the transmitting input signal 403 by the amplitude value of the receiving output signal 402 to obtain a receiving amplitude ratio 406. The transmitting amplitude ratio calculation unit 10 divides the amplitude value of the receiving input signal 401 by the amplitude value of the transmitting output signal 404 to obtain the transmitting amplitude ratio 406. The α estimating unit 1o finds the minimum value of this reception amplitude ratio 405 and outputs it as an estimated value 407 of α. The β estimator 12 finds the minimum value of the transmitted speech amplitude ratio 406 and outputs it as an estimated value 408 of β. The attenuation amount setting unit 13 calculates the attenuation amount 2G to be applied to the receiving attenuator 2 or the transmitting attenuator 7 from the estimated value 406 of d and the estimated value 408 of β. The attenuation amount setting unit 13 is configured so that the howling margin is always set to a constant value even if α and β change.
G is calculated using the following formula.

G=M/(a・β) The threshold setting unit 14 sets the estimated value of α 406 and the estimated value of β 40B.
A reception threshold 409 and a transmission threshold 410 are set from the above. The threshold setting unit 14 sets a reception threshold 409 and a transmission threshold 410.
The threshold values are calculated using equation (6) so that the values are R times the estimated value of α, 406, and the estimated value of β, 408, respectively, and that the transmitting interrupt sensitivity 2K and the receiving side interruption sensitivity are equal to 8. .

T = R@et T = R・β The transmitting/receiving determination unit 16 uses the receiving amplitude ratio 405 and the receiving threshold 409
Based on the transmission amplitude ratio 407 and the transmission threshold 410, it is determined which state should be used: transmission or reception. The transmitting/receiving determination unit 16 compares the receiving amplitude ratio 405 and the receiving threshold 409 in the receiving state, and determines that the receiving signal is transmitting when the receiving amplitude ratio 406 is greater than or equal to the receiving threshold 409, and that the receiving signal is receiving when the receiving amplitude ratio 406 is less than the receiving threshold. In the transmitting state, the transmitting amplitude ratio 407 and the transmitting threshold 410 are compared, and when the transmitting amplitude ratio 40τ is greater than or equal to the transmitting threshold 410, it is determined that the voice is being received, and when it is below, it is determined that the voice is being transmitted. The transmission/reception determination signal 41 is the determination result.
1 is sent to the receive attenuator 2 and the transmit attenuator 7. The amounts of attenuation of these two attenuators are controlled reciprocally by the transmission/reception determination signal 411, and when attenuation is inserted into one, no attenuation is necessarily inserted into the other. That is, in the receiving state, the amount of attenuation of the receiving attenuator 2 is 0, and the amount of attenuation of the transmitting attenuator 7 is set to be large. Conversely, in the transmitting state, the receiving attenuator 2
The amount of attenuation is large, and the amount of attenuation of the transmitting attenuator 7 is set to zero. As described above, the attenuation amount of the receiving attenuator 2 is 41
2, the attenuation amount of the transmitting speech attenuator 5 is controlled as shown in 413.

As described above, according to this embodiment, d and β can be accurately estimated by the α estimator and the β estimator. The threshold setting unit performs reception blocking and transmission blocking based on the estimated value of d and the estimated value of β.

An optimal reception threshold and an optimal transmission value are set so that no disconnection occurs. Based on α and β, the attenuation amount setting unit sets the attenuation amounts of the receiving attenuator and the transmitting attenuator to values as small as possible within a range that does not cause howling. Therefore, the location of the microphone and speaker.

Room reverberation characteristics 1 Even if the characteristics of the line, the characteristics of the communication equipment at the far end change, and α and β change, there will be no receiving blocking, transmitting blocking, cutting off at the beginning of the line, or howling, and the simultaneous communication will be maintained. Also can provide excellent voice switch circuit.

Effects of the Invention The present invention provides α for estimating the coupling strength of the echo path of an acoustic system: α.
The coupling strength between the estimator and the echo path of the line system: β is estimated.
By providing an estimating section, it is possible to accurately estimate d and β in the usage state, and the threshold setting section determines whether receiving blocking, transmitting blocking, or cutting off of the beginning of a speech occurs based on the estimated value of d and the estimated value of β. Set the optimal reception threshold and optimal transmission threshold. At the same time, the attenuation amount setting section controls the attenuation amounts of the receiving attenuator and the transmitting attenuator to values as small as possible within a range that does not cause howling.

Therefore, the reverberation characteristics of the nine rooms where the microphone and speaker are located, the characteristics of the nine lines, and the characteristics of the communication equipment on the far end side change, and α
It is possible to realize a voice switch circuit that does not cause reception blocking, transmission blocking, cutting off of the beginning of a conversation, or howling even when the value .beta. changes, and also has excellent simultaneous conversation performance.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an audio switch circuit in an embodiment of the present invention, Fig. 2 is a model diagram for explaining the operation, Fig. 3 is a characteristic diagram for explaining the switching operation, and Fig. 4 is the same as that of Fig. 1. FIG. 6 is a block diagram of a conventional audio switch circuit, and FIG. 6 is a waveform diagram of signals at each portion of FIG. 5. 2... Receiving attenuator, 7... Sending attenuator, 9... Receiving amplitude ratio calculation unit, 1o...
α estimation section, 11... Transmission amplitude ratio calculation section, 12.
....beta estimation section, 13..attenuation amount setting section,
14...Threshold value setting section, 15...Transmission/reception determination section. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 5s ゛Figure 3 Log (K) Figure 4 Figure 5

Claims (1)

[Claims] There is a receiver attenuator that attenuates and outputs the receiving input signal in the transmitting state, and outputs it as the receiving output signal without attenuating it in the receiving state, and a receiver attenuator that attenuates and outputs the transmitting input signal in the receiving state and outputs it without attenuating it, and in the transmitting state. A transmitting attenuator that outputs the transmitting output signal as it is without attenuation; a receiving amplitude ratio calculator that calculates a receiving amplitude ratio by dividing the amplitude of the transmitting input signal by the amplitude of the receiving output signal; an α estimation unit that estimates a coupling strength α of a reverberation path of an acoustic system formed between the output end of the receive attenuator and the input end of the transmit attenuator from the value of the amplitude ratio; a transmitting amplitude ratio calculation unit that calculates a transmitting amplitude ratio by dividing the amplitude of the transmitting output signal by the amplitude of the transmitting output signal; and a transmitting amplitude ratio calculation unit that calculates a transmitting amplitude ratio by dividing the amplitude of the transmitting output signal by the amplitude of the transmitting output signal; A β estimating unit that estimates the coupling strength of the echo path of the line system formed between the end of the line and the attenuation of the receiving attenuator and the transmitting attenuator from the estimated value of α and the estimated value of β. a threshold setting unit that sets a receiving threshold and a transmitting threshold from the estimated value of α and the estimated value of β; and a threshold setting unit that monitors the receiving amplitude ratio in the receiving state and If the amplitude ratio is less than or equal to the reception threshold, the reception state is maintained, and if it is greater than or equal to the reception threshold, the transmission state is entered.In the transmission state, the transmission amplitude ratio is monitored, and the transmission amplitude ratio is When the transmitting threshold is below, the transmitting state is maintained; when the transmitting threshold is just above the transmitting threshold, the transmitting state is changed to the receiving state, and the transmitting/receiving device controls the receiving attenuator and the transmitting attenuator based on the determination result of the transmitting/receiving. A voice switch circuit comprising: a determining section.