JPS61195048A - Voice switch circuit of loudspeaking telephone set - Google Patents

Abstract

PURPOSE:To make it difficult for malfunction to occur, which is caused by the peripheral noise of a transmission/reception call switching circuit by comparing a call input inputted through a microphone with a low pass call input through an LPF so as to discriminate the peripheral noise. CONSTITUTION:Where a voice is added, the level ration of an LF call input level passing through the LPF 20 to that before passing is raised because of a low loss level. In case of only a noise the level ration becomes high due to a high cut ration by the LPF 20. Accordingly the sound of a threshold setting circuit 22 and the reference level of the noise discrimination are set, and a level comparator circuit 23 compares them so as to discriminate the sound from the noise. Here, when the output of the comparator circuit 23 is 'H', it is discriminated to be a voice, and therefore an analog switch 24 is turned on to input the call input to a comparator circuit 13, whereby the normal transmission/reception call switching is executed. On the other hand, when the output of the circuit 23 is 'L', the transmission call input form a microphone 1 is judged to be the peripheral noise to turn off the switch 24, and the transmission call level is not inputted to the circuit 13, thereby preventing malfunction.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field 1 The present invention relates to a voice switch circuit for a loudspeaker telephone that allows hands-free communication.

[Background Art] In general, in this type of loudspeaker telephone that is equipped with amplifying means for amplifying each of the transmitting signal and the receiving signal and is capable of communicating with the hand 717-, an audio switch circuit is provided to prevent howling. There is. FIG. 1 shows an audio switch circuit for a loudspeaker telephone according to the present invention, which includes a microphone 1, amplifiers 2, 4, 5, 7, 9, and 11 for amplifying the transmitting signal or the receiving signal, and the transmitting and receiving signals. variable loss circuits 3 and 8 for suppressing the amplification degree of the amplification means for use and reception;
A speaker 10, a rectifying and smoothing circuit 6゜12 that rectifies and smoothes the transmitting signal and receiving signal amplified by the amplifiers 5 and 11 to form a transmitting level signal and a receiving level signal, and outputs of the rectifying and smoothing circuits 6 and 12. Comparison circuit 13 and comparison circuit 1
The control means 14 controls the variable loss circuits 3 and 8 based on the three outputs, and a side sound prevention circuit 15. By the way, in this loudspeaker telephone, the sound emitted from the speaker 10 is input to the microphone 1, and if the near end-toward gain and the far end-toward gain are 1 or more, howling will occur. Note that the near-end loop gain is the gain of the loop in which the speaker 10 and the microphone 1 are coupled via the side-blocking sound circuit 15 of the own telephone, and the far-end loop gain is the gain of the loop in which the speaker 10 and the microphone 1 are coupled via the side sound protection circuit 15 of the own telephone. is the gain of the containing loop.

A variable loss circuit 3.8 is provided to reduce the above-mentioned near end-return gain and far end-return gain to 1 or less, and when transmitting, the transmitting and receiving levels are compared because the transmitting level is high. In response to the output of the comparison circuit 13, the control means 14 reduces the loss of the variable loss circuit 3 of the transmitting amplifying means, and increases the loss of the variable loss circuit 8 of the receiving amplifying means, On the other hand, when receiving a call, since the receiving level is high, the variable loss circuit 3 of the transmitting amplification means receives the output of the comparison circuit 13 and is controlled by the control means 14
The loss of the variable loss circuit 8 of the receiving amplification means is reduced. By the way, the voice during a call is not continuously at a constant level, but there are pauses in the voice during which there is no sound, and a portion of the transmitting signal leaks from the side sound protection circuit 15 and is input to the amplifier 7, and the level increases to a high level. The transmitter may be amplified, and when transmitting, the receiving level input of the comparison circuit 13 becomes larger than the transmitting level input, and the control states of the variable loss circuits 3 and 8 are reversed. In addition, because the sound from the speaker 10 is not input to the microphone 1 when receiving a call, reception blocking may occur. Therefore, in order to prevent such inconvenience from occurring, a time constant circuit is provided in at least one of the rectifying and smoothing circuit 6.12 and the comparator circuit 13, so that the state of the output of the comparator circuit 13 is maintained even during a silent pause period during a call. I'm trying not to flip it.

By the way, in such a conventional example, a pair of rectifier charging circuits 16m as shown in FIG. A noise speech discrimination circuit 16 consisting of a noise speech discrimination circuit 16b and a comparison circuit 16c is provided, and the output of the rectification and smoothing circuit 6 is inputted to the comparison circuit 13 only when the transmission input from the microphone 1 is determined to be speech. However, the rectifier charging circuit 16m is set so that charging time>discharging time, and the rectifying charging circuit 16b is set so that charging time>discharging time. Now, the transmitting input input via the microphone 1 is sent to the rectifier charging circuit 16a.

16b, for voices with rapid changes, the output of the rectifier charging circuit 16b is the output of the rectifier charging circuit 16a, whereas for steady noise with gradual changes, the output of the rectifier charging circuit 16b is the output of the rectifier charging circuit 16b. This becomes the rectifier charging circuit 16a output. Therefore, by determining the magnitude of the outputs of both the rectifying charging circuits 16a and 16b using the comparing circuit 16c, it is possible to distinguish between ambient noise and voice. However, the ambient noise does not necessarily change gradually; for example, 1! l II 41k 9L -s km klr
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In the conventional example, such ambient noise is not regarded as noise, but is determined as voice, and there is a problem in that the transmitting/receiving switching circuit malfunctions due to the ambient noise.

[Objective of the Invention 1 The present invention has been made in view of the above points, and its purpose is to make it possible to transmit and receive calls even if the ambient noise is periodic or pulse-like. It is an object of the present invention to provide a voice switch circuit for a loudspeaker telephone in which malfunctions due to ambient noise in the switching circuit are less likely to occur.

DISCLOSURE OF THE INVENTION 1 (Embodiment) FIG. 2 shows a circuit diagram of a main part of an embodiment of the present invention, and the schematic configuration is the same as that in FIG. 1, and the basic operation is also the same.

Here, the feature of the present invention is that the microphone 1
Other than the voice band of the transmitting input input via the (for example,
Low-pass filter 20 that cuts frequencies above 3KHz
, a level comparison circuit 23 that detects the level ratio between the transmission input and the low-pass transmission input passed through the low-pass filter 20; and the output of the level comparison circuit 23 that turns on and off and inputs the transmission level to the comparison circuit 13. In Figure 6, the rectifier and smoothing circuit 21 is equivalent to the rectifier and smoother circuit 6, and the output of the rectifier and smoother circuit 21 is (Speech input level that does not pass through the low-pass filter 20)
is input to one input terminal of the level comparison circuit 23 via the threshold setting circuit 22, and the threshold setting circuit 22
is formed by a volume that appropriately divides the transmitting input level to form a reference level. On the other hand, the rectifying and smoothing circuit 6 is configured to receive the transmitting input that has passed through the low-pass filter 20 and output a low-pass transmitting level, and the level comparing circuit 23 receives the input signal from the threshold setting circuit 22. The reference level and the low-pass transmission level are compared, and when the output of the level comparison circuit 23 is 'H' level, the switch 24 is turned on, and when the output of the level comparison circuit 23 is 'L'', the switch 24 is turned off. .

The control means 14 includes a charging/discharging circuit 14a that prevents cutting of endings and beginnings of words when switching between sending and receiving calls;
11 output, and a switching control circuit 14b that operates either variable loss circuit 3 or 8 based on the output of 11.

The operation of the embodiment will be described below. Now, when we analyze the spectrum of the audio waveform, as shown in IJIJ3 figure (a), the level becomes flat and low above 5 kHz. Additionally, ambient noise is generally considered to be a spectrum with peaks at random positions as shown in Figure 3(b), and in a state where voice and ambient noise are mixed, the spectrum is as shown in Figure 3(c). considered to be a condition. In addition, the 7t Le Manto (
The frequency components that characterize vowels differ depending on the length of the vocal tract, but normally there are 3.4 of them up to about 3KHz, and 3.
It is thought that there is no problem in speech recognition even if there are no components of KHz or higher. (For example, the first part of the Technical Standards of the Telegraph and Telephone Public Corporation
In Article 9, the frequency range is 300Hz-3.4KHz. ) Therefore, if the signal is passed through the steep low-pass filter 20 having a cutoff frequency of about 3 KHz, the noise level cut ratio will be much larger than the voice level cut ratio. Taking this into consideration, when there is voice, the level ratio of the low-pass transmitting speech input level passed through the low-pass filter 20 and the transmitting speech input level before passing through will be high because the loss level is small, and only noise will be present. In this case, the cut ratio by the low-pass filter 20 is large, so the level ratio becomes low. Therefore, threshold setting circuit 2
A reference level for voice/noise discrimination in step 2 is set, and a level comparison circuit 23 compares it to discriminate whether it is voice or noise. Here, if the output of the level comparison circuit 23 is "H", it means that it is determined to be voice, so the switch 24 is turned on and the transmitting input level is input to the comparison circuit 13, and normal transmission and reception are performed. On the other hand, if the output of the level comparison circuit 23 is L'', it means that the transmitting input input through the microphone 1 is determined to be ambient noise, so the switch 24 is turned off. The transmitting level is not input to the comparison circuit 13, thereby preventing malfunction of the transmitting/receiving switching circuit due to ambient noise.

In addition, in order to satisfy Article 19 of the above-mentioned Telephone and Telecommunications Public Corporation Standards, a low-pass filter equivalent to the four-pass filter 20 of the present invention is required, so by sharing this low-pass filter, the number of parts can be reduced. It is now possible to reduce costs.

[Effects of the Invention 1] As described above, the present invention is a voice switch circuit that prevents howling by controlling the amplification degree of a loudspeaker telephone equipped with amplifying means for amplifying the transmitting signal and the receiving signal, respectively. a rectifying and smoothing circuit that rectifies and smoothes the signal and the received signal to detect the transmitting level and the receiving level;
A voice switch circuit for a public address telephone comprising a comparison circuit for comparing a transmission level and a reception level, and a control means for controlling the amplification degree of the transmission and reception amplification means based on the output of the comparison circuit. a mouth-pass filter that cuts out the voice band of the transmitting input input through the
A level comparison circuit that detects the level ratio between the transmitting input and the low-pass transmitting input that has passed through the draw-pass filter, and a switch that is turned on and off at the output of the level comparing circuit to control the input of the transmitting level to the comparison circuit. This system is equipped with a malfunction prevention circuit that detects ambient noise by comparing the speaker input through the microphone and the low-pass voice input passed through a low-pass filter. Even if it is sexual or pulse-like,
This has the effect that malfunctions due to ambient noise in the transmitting/receiving switching circuit are less likely to occur.

[Brief explanation of the drawing]

Fig. 1 is a block circuit diagram of the audio circuit of a loudspeaker telephone according to the present invention, Fig. 2 is a block circuit diagram of a main part of an embodiment of the present invention, Fig. 3 is an explanatory diagram of the same operation, and Fig. 4 is a conventional example. FIG. 1 is a microphone, 6.12 is a rectifier and smoothing circuit, 13 is a comparison circuit, 14 is a control means, 20 is a low-pass filter, 2
3 is a level comparison circuit, and 25 is a malfunction prevention circuit.

Claims (1)

[Claims] (1) A voice switch circuit that prevents howling by controlling the amplification degree of a loudspeaker telephone equipped with amplification means for amplifying the transmitting signal and the receiving signal, the circuit rectifying and smoothing the transmitting signal and the receiving signal, respectively. A rectifying and smoothing circuit that detects the transmitting level and the receiving level, a comparison circuit that compares the transmitting level and the receiving level, and a control means that controls the amplification degree of the transmitting and receiving amplification means based on the comparison circuit output. In an audio switch circuit for a public address telephone, comprising:
A low-pass filter that cuts out the audio band of the transmitting input that is input through the microphone, a level comparison circuit that detects the level ratio between the transmitting input and the low-pass transmitting input that has passed through the low-pass filter, and the level comparison circuit output. 1. An audio switch circuit for a loudspeaker telephone, comprising a malfunction prevention circuit comprising a switch that is turned on and off to control input to a transmitting level comparison circuit.