JPS59126331A - Voice switching circuit - Google Patents

Abstract

PURPOSE:To prevent the beginning of a talk from being cut and to improve the quality of telephone service by providing a delay circuit in front of a variable loss circuit to which a signal is inputted after its transmission or reception level is read out. CONSTITUTION:A means level inputted from a line L and obtained through a rectifying circuit 5 for a receive signal is compared by a comparator 4 with a mean level inputted from a transmission-side circuit Ls and obtained through a rectifying circuit 3 for a transmit signal and variable loss circuits 1 and 8 are controlled to make the circuit 1 and 8 high loss and low loss respectively; and a speech signal is passed through delay circuits 9 and 10 to be delayed by times corresponding to the control delay of variable loss circuits 1 and 8, and then inputted to the variable loss circuits 1 and 8. The delay-release time of level detection is set similarly with a conventional voice switch circuit, so the delay time is set to between a value of a high-loss low-loss and a value of low-loss high-loss switching time so that the output (a) of the variable loss circuit 1 is an output free of the cutting of the beginning of a talk.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to an audio switch circuit using a variable loss circuit to prevent howling in a 2-wire to 4-wire conversion circuit.

(2) Prior Art and Problems For example, in a 2-wire to 4-wire conversion circuit provided in a telephone terminal, etc., an audio switch is provided as a howling prevention means. FIG. 1 is a diagram illustrating the conventional early formation of such a voice switch, and shows L8. LR indicates the sending line and receiving line among the 4 lines on the terminal side, L indicates the 2-line line, and 1
．． 8 is a transmitting and receiving variable loss circuit, 2.7 is an amplifier, 3
．． 5 is a rectifier circuit, 4 is a comparator, and 6 is a side noise prevention circuit such as a hybrid coil. How many times have you sent it? The transmission signal from fM L s is amplified by an amplifier 2 via a variable loss circuit 1, and sent to the line via a side sound protection circuit 6. On the other hand, the reception signal from the other party passes through the FULL sound circuit 6, the variable loss circuit 8, the amplifier 7, and is amplified and received by the receiving line LR.Therefore, the receiving line LH is connected to a speaker, and the transmitting side When a microphone or the like is connected to the circuit Ls, audio from a speaker is input to the microphone, and if the near-end to loop gain and far-end to loop gain are 1 or more, howling will occur. is the loop gain when the line L B + L a is coupled via the side sound protection circuit 6 of the own terminal t111, and the far end-to-loop gain is the gain of the loop including the other terminal, etc. In order to reduce the illumination rate to 1N, a variable loss circuit 1 is provided in the transmitter circuit, a variable loss circuit 8 is provided in the receiver circuit, and the comparator 4 Compare the speaking level and the receiving level, and when transmitting, when the transmitting level is high, 1lilJ is controlled so that the loss of variable loss circuit 1 is small and the loss of variable loss circuit 8 is large, and when receiving a call, the receiving level is By increasing the level, the loss of the variable loss circuit 1 is controlled to be large and the loss of the variable loss circuit 8 is controlled to be small.

Furthermore, the rectifier circuit 3.5 includes a time constant circuit to prevent the output state of the comparator 4 from inverting during a short pause period during a call, and to prevent the hangover time from occurring, for example, from 200 to 300m5. It is set.

However, because there is a delay time until the average level of the audio is detected due to the output of the rectifier circuit 3.5, there is a problem that the control of the variable loss circuit 1.8 does not follow the instantaneous level changes of the audio signal. (O) This has the disadvantage that the beginning of the speech is cut off, that is, the beginning of the speech is cut off, and the quality of the call deteriorates.
.

Furthermore, if the time for level detection is shortened in order to shorten the time for cutting off at the beginning of a conversation, the variable loss circuit operates frequently, which impairs the naturalness of the conversation.

(3) Purpose of the Invention In view of the above-mentioned problems, the present invention provides control of the audio signal input to the variable loss circuit in order to eliminate cutting-off at the beginning of speech due to control delay of the variable loss circuit, etc. It is an object of the present invention to provide a voice switch circuit that delays according to the delay time.

(4) Structure of the Invention In order to achieve the above object, the present invention compares the transmitting level and the receiving level, and based on the result, the variable loss circuit provided in the transmitting circuit and the variable loss circuit provided in the receiving circuit. The audio switch circuit controls the loss circuit reciprocally, and is characterized by comprising a delay circuit at the front stage of the variable loss circuit which is input after extracting the transmitting level and the receiving level.

3- (5) Examples of ζchimei The present invention will be explained in more detail in Example 1 below.

FIG. 2 shows an embodiment of the audio switch circuit of the present invention.
FIG. In FIG. 2, the same symbols as in FIG. 1 indicate the same objects, and 9.10 is a delay circuit. A comparator 4 compares the average level input from the Katsuji line and obtained via the rectifier circuit 5 of the received signal and the average level input from the transmission/side line and obtained via the rectifier circuit 3 of the transmit signal. The variable loss circuit 1.8 is controlled to have high loss or low loss, and the speech signal is transmitted through the delay circuit 9゜1.
0, the signal is delayed by a time corresponding to the control delay of the variable loss circuit 1.8 described above, and is input to the variable loss circuit 1.8.

Figure 3 shows the transmitting line L of the 2-wire to 4-wire conversion in Figure 2.
8 is a time chart illustrating an example of the operation. Third
(A) to (E) in the figure correspond to (A) to (E) in FIG. 2, and (E) shows an example of how the circuit appears in the conventional circuit. The input signal (a) inputted from the line L8 is delayed by a fixed time td by the delay circuit 9, and becomes the input signal (b) to the variable loss circuit 10. Ota,
A part of the input signal (A) passes through the rectifier circuit 3 and an average of 1 novel (C) is detected. This average level (c) is times IN
The comparator 4 compares the average level of the speech signal received from L, and when it becomes larger than the threshold value Ath, the variable loss circuit 1 can be switched from high loss to low loss state) This switching from high loss to low loss The operation time required for is t.

On the other hand, the recovery time from when the signal input from the side iLs disappears until the variable loss circuit 1 is switched from low loss to high loss requires tr.

The delay-recovery times ta and tr in level detection are set so that ta < tr as in the conventional audio switch circuit, so the delay time td is set to 1. <ta
By setting <tr, the output (E) of the variable loss circuit 1 becomes an output without cutting off the beginning of a speech.

Even if we compare this output (E) with the output without a conventional delay circuit (E), we can see that in the conventional variable loss circuit, the transmitting signal is input when the loss is high, so this output may be cut off at the beginning of the line, resulting in a conversation. It can be seen that while the quality deteriorates, the present invention improves the quality.

In the above explanation, the transmission of Ls→L was explained to the king, but L→L
The same explanation applies to the reception of 0. Here, as is known, even if the delay in the call signal is quite large when the echo is small, it does not impede the naturalness of the call.
According to the present invention, the tan tan tr time can be set freely as long as the condition % ta<td<tr is satisfied. Therefore, in order to reduce the disconnection at the beginning of speech unlike in the conventional circuit, t
It is not necessary to set tl to be short, and according to the present invention, by setting tl appropriately long, the voice switch circuit can be operated stably without frequent switching.

(6) As described in detail, according to the present invention, a circuit for delaying the call signal is provided on the input side of the variable loss circuit, and a manual signal extraction for level detection and a delay at the time of input to the variable loss circuit are provided. This prevents the beginning of the speech from being cut off.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional voice switch circuit, FIG. 2 is a block diagram of an embodiment of the voice switch circuit of the present invention, and FIG. 3 is a block diagram of a conventional voice switch circuit.
It is an operation time chart of the figure. 1.8 is a variable loss circuit, 9.10 is a delay circuit, 4 is a comparison circuit, and 3.5 is a rectifier circuit.

Claims (1)

[Claims] An audio switch circuit that compares a transmitting level and a receiving level, and reciprocally controls a variable loss circuit provided in a transmitting circuit and a variable loss circuit provided in a receiving circuit based on the result. and the transmitting level. An audio switch circuit characterized in that a delay circuit is provided at the front stage of a variable loss circuit that is input after extracting a reception level.