JPH03191692A - Method and device for noise suppression voice signal conversion - Google Patents

Abstract

PURPOSE:To suppress noise generation due to a speech line control signal by converting an analog voice signal from analog to digital, and generating a digital voice signal which is delayed by a specific time, and selecting and sending out a delayed digital voice signal only when the speech line control signal is received. CONSTITUTION:The analog voice signal which is inputted from an analog speech line 10 is passed through a 2-line/4-line converting circuit 2 and inputted to the input terminal 6a of an output selecting circuit 6 through an A/D converter 3. The circuit 6 is so controlled by a control circuit 4 that the signal inputted to the terminal 6a is normally outputted. Then when a pulse signal for charging, etc., is sent out, the circuit 4 sends out an output switching control instruction to the circuit 6 in synchronism with a charging control signal transmission instruction to a control signal transmitting and receiving circuit 1. The circuit 6 receives the control instruction to perform switching to a signal which is inputted to the terminal 6b and passed through a delay circuit 5. Consequently, no noise is outputted from the circuit 6 when the delay time of the circuit 5 is adjusted to the length of a generated noise.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a noise suppressing voice signal conversion method and device, and in particular to a speech line control signal when converting between an analog voice signal and a digital voice signal in a telephone switching system. The present invention relates to an audio signal conversion method and apparatus for suppressing noise generation due to transmission and reception of audio signals.

[Conventional technology]

Conventionally, this type of voice signal converter includes a control signal transmitting/receiving circuit that transmits and receives call line control signals to and from the opposing exchange via an analog call line, a 2-wire/4-wire converter circuit, and an analog/digital converter circuit. There is a device (trunk) consisting of a control circuit and a control circuit.

As a measure to prevent noise from entering the audio signal of this device, as shown in FIG. There is a system in which the analog-to-digital conversion function is stopped only when noise occurs by controlling the power down of the circuit 3, so that only subscribers on the digital communication line 11 side cannot hear the noise.

[Problem to be solved by the invention]

The conventional audio signal conversion device described above uses a telephone line to transmit and receive a telephone line control signal. The audio signal is alternating current and the control signal is direct current, so there is usually no problem, but when transmitting and receiving control signals during a call, the transient phenomenon at the moment of switching appears to be alternating current, and is input to the analog-to-digital conversion circuit as an audio signal. This causes noise.

In order to reduce this noise, a method of inserting a filter between the telephone line and the telephone line control signal transmitting/receiving circuit reduces the noise by suppressing transient phenomena, but at the same time, the telephone line control signal cannot be identified. It becomes difficult. Furthermore, depending on the opposing device, the communication line may be restored by misrecognizing it as a restoration signal. Therefore, it is not possible to install a filter that makes the noise completely inaudible.

In addition, with the method of power-down control of the analog-to-digital conversion circuit, the audio is interrupted only while the power-down control is being performed, and the audio is interrupted due to the instability of the output when the power is turned on (the analog-to-digital conversion function is restored). The problem is that the level suddenly increases or fluctuates, so the person on the phone can hear it as noise.

SUMMARY OF THE INVENTION An object of the present invention is to provide a noise-suppressing audio signal conversion method and device that suppresses noise generation in digital audio signal output when transmitting and receiving call line control signals.

[Means to solve the problem]

The noise suppression voice signal conversion method of the present invention transmits and receives a voice line control signal between an opposing exchange via an analog voice line, and converts an analog voice signal on the analog voice line and a digital voice signal on the digital voice line. In the audio signal conversion method, an analog audio signal input from the analog telephone line is converted into a corresponding first digital audio signal, and a second digital audio signal delayed by a predetermined time from the first digital audio signal is converted into a corresponding first digital audio signal. When the first digital voice signal is not transmitted or received, the first digital voice signal is selected and sent to the digital telephone line, and the first digital voice signal is selected and transmitted to the digital telephone line, and the first digital voice signal is not transmitted or received. When performing either of these, the second digital audio signal is selected and sent to the digital communication line.

The noise suppression voice signal converter of the present invention is a voice signal converter that interfaces an analog call line and a digital call line, and transmits and receives a call line control signal to and from an opposing exchange connected to the analog call line. A control signal transmitting/receiving means, an analog-to-digital converting means for mutually converting an analog voice signal on the analog telephone line and a digital voice signal on the digital telephone line, and a digital voice signal output from the analog-to-digital converting means. a delay means for delaying the signal for a predetermined period of time, and one of the digital audio signals output from each of the analog-to-digital conversion means and the delay means under control from the control signal transmitting/receiving means and output to the digital communication line. and output selection means.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. A control signal transmitting/receiving circuit 1 is connected to the analog communication line 10, which transmits and receives communication line control signals to and from the opposite exchange, and converts the communication line between 2-wire and 4-wire to provide bidirectional (2-wire) analog audio. An analog/digital conversion circuit 3 that mutually converts analog audio signals and digital audio signals via a 2-wire/4-wire conversion circuit 2 that performs mutual conversion between signals and unidirectional (4-wire) analog audio signals. It is connected. The digital output side of the analog-to-digital conversion circuit 3 is
directly connected to one input terminal 6a of the output selection circuit 6,
It is connected to the other input terminal 6b of the output selection circuit 6 via a delay circuit 5 that delays the digital audio signal for a predetermined period of time. The output side of the digital communication line 11 is connected to the output side of the output selection circuit 6, and the input side is connected to the digital input side of the analog-to-digital conversion circuit 3.

The control circuit 4 monitors the status and controls the operation of each of the circuits mentioned above.

Next, the operation will be explained.

An analog voice signal input through an analog telephone line 10 passes through a 2-wire/4-wire conversion circuit 2 and is input into an analog/digital conversion circuit 3.

The audio signal converted into a digital signal by the analog-to-digital conversion circuit 3 is sent to the input terminal 6 of the output selection circuit 6.
input to a. The output selection circuit 6 is normally controlled by the control circuit 4 so that the signal input to the input terminal 6a is output, and the digital audio signal output from the analog-to-digital conversion circuit 3 is directly used as an output signal. It is sent to the digital telephone line 11.

Some call line control signals come into the voice signal as noise, such as billing pulse signals.

Therefore, when this type of control signal is sent, the control circuit 4 sends an output switching control command to the output selection circuit 6 in synchronization with the charge control signal sending command to the control signal transmitting/receiving circuit 1. Upon receiving this control command, the output selection circuit 6 switches the output from the signal input to the input terminal 6a to the signal input to the input terminal 6b. The signal input to the input terminal 6b is a digital audio signal passed through the delay circuit 5. Therefore, if the delay time of the delay circuit is adjusted to the length of the generated noise, the signal input to the input terminal 6b will be output only during the time when the noise is generated, and the noise will be removed from the output selection circuit 6. Therefore, only the subscriber on the digital communication line 11 side can no longer hear the noise.

Next, the timing of output switching and changes in audio signals will be explained. FIG. 3 is a time chart showing an example of audio signals from the input terminals 6a, 6b and the output section of the output selection circuit 6 shown in FIG. 1, and shows an example of noise generated during billing control.

The signal at the input terminal 6a is sent to the analog-to-digital conversion circuit 3.
Normally, this signal is used as the output of the output selection circuit 6. The signal at the input terminal 6b is
The output from the analog-to-digital conversion circuit 3 is passed through the delay circuit 5, and is delayed from the signal at the input terminal 6a by a certain time Td (for example, 2m5). Now, the charging control time (
It is assumed that Tn (corresponding to the noise generation time) satisfies Td≧Tn.

If charging control starts at tl and ends at t2, noise will be introduced into the signal at the input terminal 6a between t1 and t2.

Since the input terminal 6b receives a signal delayed by Td, the signal between t1 and t2 is input to the input terminal 6a (2tl-t2).
) to t1. Here, the output selection circuit 6
Therefore, if the signal at the input terminal 6b is output only between t1 and t2, it is possible to prevent noise from entering the output signal. Note that since many audio signals are periodic, the repetition of the same audio signal for about 2 mS will not cause any trouble in listening to the audio.

〔Effect of the invention〕

As explained above, the present invention replaces a digital voice signal in which noise has occurred due to the transmission and reception of a telephone line control signal with a signal immediately before the noise, so that subscribers on the digital telephone line side can hear the noise. There is an effect that can prevent it from happening.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing an example of a conventional audio signal converter, and FIG.
FIG. 1 is a time chart showing an example of the audio signal of the output selection circuit of FIG. 1... Control signal transmission/reception circuit, 2... 2-wire/4-wire conversion circuit, 3... Analog/digital conversion circuit, 4...
- Control circuit, 5... Delay circuit, 6... Output selection circuit, 10... Analog telephone line, 11... Digital telephone line.

Claims (1)

[Claims] 1. Communication line control signals are transmitted and received between an opposing exchange via an analog communication line, and the analog voice signal on the analog voice line and the digital voice signal on the digital voice line are exchanged. In the audio signal conversion method for converting an analog audio signal input from the analog telephone line into a corresponding first digital audio signal,
A second digital audio signal delayed by a predetermined time from the first digital audio signal is generated, and when the communication line control signal is not transmitted or received, the first digital audio signal is selected and transmitted to the digital communication line. A noise suppressing voice signal conversion method, characterized in that when transmitting or receiving the telephone line control signal, the second digital voice signal is selected and transmitted to the digital telephone line. 2. In a voice signal conversion device for interfacing an analog telephone line and a digital telephone line, a control signal transmitting/receiving means for transmitting and receiving a telephone line control signal between an opposing exchange connected to the analog telephone line; an analog-to-digital conversion means for mutually converting an analog voice signal on the line and a digital voice signal on the digital communication line; and a delay means for delaying the digital voice signal output from the analog-to-digital conversion means for a predetermined period of time; and output selection means for selecting one of the digital audio signals output from each of the analog-to-digital conversion means and the delay means and outputting it to the digital communication line according to control from the control signal transmission and reception means. A noise suppression audio signal conversion device characterized by: