JPS63177636A - In-band tone transmitting system - Google Patents

Abstract

PURPOSE:To surely prevent a loss of a tone signal by clipping a sound signal in advance at a transmitting side, and superposing the tone signal to this clipped sound signal and sending it out to a transmission line. CONSTITUTION:Between an amplifier 14 of a transmitting side and a synthesizer 13, a clipping circuit 17 is provided. This clipping circuit 17 has a clip level which has been set to a smaller level than a sound signal level corresponding to a dynamic range of a transmission line, and clips an amplified sound signal by this clip level. Accordingly, a tone signal which has been led into the synthesizer 13 through a press-to-talk switch 12 is superposed to the sound signal clipped by the clipping circuit 17, by the synthesizer 13 and sent out to a transmission line 8. Therefore, it does not occur that the sound signal is clipped in the course of transmission, and as a result, a loss of the tone signal is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an improvement in an in-band tone transmission method applied to, for example, a voice wireless communication system.

(Prior Art) In recent years, various communication systems have been developed in line with the diversification of communication needs. Among them, for example, there is a system that allows voice calls to be made between an extension telephone terminal and a wireless telephone terminal using a private branch exchange. There is a system that does this. FIG. 3 shows an example of its configuration. This system connects a private branch exchange (PBX) 2 to which an extension telephone terminal 1 is connected and an iwIIa base 8 device 4 to which a wireless telephone terminal 3 is connected. It is connected via a transmission path 8 consisting of a carrier end station device 5.6 and a wireless line 7.

By the way, in this type of system, communication between the extension telephone terminal 1 and the wireless telephone terminal 3 is carried out by, for example, a breath talk communication method, but in this case, the transmission of breath talk information is generally carried out by an in-band tone method. . The in-band tone method transmits information by superimposing a low-level tone signal on a voice signal as a main signal, and is conventionally configured as shown in FIG. 4, for example. That is, a tone signal generating circuit 11 is provided on the transmitting side, for example, the PBX 2, and the tone signal generated from the tone signal generating circuit 11 is switched on and off by a pre-stoke switch 12 and then introduced into a combiner 13. The synthesizer 13 superimposes the tone signal on the audio signal amplified by the amplifier 14 as shown in FIG. On the other hand, at the receiving side, for example, the radio telephone terminal 4, the audio signal that has arrived via the transmission path 8 is introduced via the transformer 21, amplified by the amplifier 22, and then output to an audio output circuit (not shown) to be sent out as audio. At the same time, the audio signal is passed through a bandpass filter 23 to separate and extract only the tone signal component and introduced into a tone detector 24, which detects the presence or absence of a tone signal and displays the result on a light emitting diode or the like. It is displayed on the device 25. In such a system, since the tone signal is at a low level, it is possible to transmit breathtalk information without practically affecting voice communication.

However, since audio signals generally have a wide signal level range, the peak of the signal waveform may be clipped during transmission depending on the dynamic range of the transmission path. For this reason, in the conventional method in which the tone signal is simply superimposed on the audio signal, when the audio signal is clipped, the fifth
As shown in Figure (b), the tone signal was lost and information was missing, which was very undesirable.

(Problems to be Solved by the Invention) As described above, the conventional in-band tone transmission method has the problem that tone signal loss occurs depending on the dynamic range of the transmission path, making it impossible to accurately transmit information. The present invention focuses on this point, and makes it possible to reliably transmit tone signals without loss even when the dynamic range of the transmission path is narrow, thereby achieving accurate information transmission and one in-band tone transmission The aim is to provide a method.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a clipping circuit having a clipping level set according to the dynamic range of the transmission path on the transmission side, and clips the audio signal with the clipping circuit. do,
A tone signal is superimposed on this clipped audio signal and transmitted.

(Function) As a result, the audio signal sent from the transmitting side to the transmission path has already had the leading part of the signal waveform clipped, so even if the dynamic range of the transmission path is narrow, the audio signal is transmitted on this transmission path. will no longer be clipped. Therefore, the problem that the tone signal superimposed on the audio signal is lost during transmission does not occur, and therefore the information by the tone signal is reliably transmitted without any loss.

(Embodiment) FIG. 1 is a block diagram of a voice communication system to which an in-band tone transmission method is applied in an embodiment of the present invention. In this figure, the same parts as in FIG. 4 are given the same reference numerals and detailed explanations will be omitted.

A clip circuit 17 is provided between the audio signal amplifier 14 and the synthesizer 13 on the transmitting side. This clip circuit 1
7 has a clip level set to a lower level than the audio signal level corresponding to the dynamic range of the transmission path, and the amplified audio signal is clipped according to this clip level. Therefore, the tone signal introduced into the synthesizer 13 via the breath-talk switch 12 is superimposed on the audio signal clipped by the clipping circuit 17 in the synthesizer 13 and sent to the transmission line 8. FIG. 2 shows the signal waveform after this superimposition.

Therefore, the audio signal is not clipped during transmission, and as a result, loss of the tone signal is prevented.

In this embodiment, the audio signal is clipped in advance on the transmitting side, and the tone signal is superimposed on the clipped audio signal before being sent to the transmission path. Clipping can be prevented, thereby reliably preventing loss of tone signals. Therefore, information transmission using tone signals can be performed reliably without errors, and the operational reliability of the system can be improved. Note that clipping the audio signal will cause distortion in the audio signal, but in general, audio has a property that the clarity does not deteriorate even if clipping distortion occurs, so the above-mentioned clipping will cause distortion in the audio signal. There are almost no negative effects.

Note that the present invention is not limited to the above embodiments. For example, although the clip level of the clip circuit is fixed in the above embodiment, it may be made variable. In this way, it is possible to set the optimum lip level according to the dynamic range of the transmission path. In addition, various modifications may be made to the configuration and installation position of the clip circuit, the configuration of the communication system, the type of information transmitted by tone signals, etc. without departing from the gist of the present invention.

[Effects of the Invention] As detailed above, according to the present invention, a clipping circuit having a clipping level set according to the dynamic range of the transmission path is provided on the transmitting side, and the audio signal is clipped by this clipping circuit. By transmitting the clipped audio signal with the tone signal multiplied by m, even if the dynamic range of the transmission path is narrow, the 1-tone signal can be reliably transmitted without loss. An in-band tone transmission method that allows more accurate information transmission can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram of a voice communication system to which an in-band tone transmission method is applied in an embodiment of the present invention;
Figure 2 is a signal waveform diagram of a tone signal @ superimposed voice signal transmitted by the same system, Figure 3 is a schematic configuration diagram showing an example of a voice communication system, and Figure 4 is a diagram of a conventional in-band tone transmission method. Block configuration diagram of the applied communication system,
FIG. 5 is a signal waveform diagram for explaining the method. 1...Inside I! J Telephone terminal, 2... Private branch exchange tM (
PBX), 3...wireless telephone terminal, 4...no li! Base station equipment, 5.6... Carrier terminal station @ location, 7... Wireless line, 8... Transmission line, 11... Tone signal generation circuit,
12...Breath talk switch, 13...Synthesizer,
14.22...Amplifier, 15.21...Transformer,
23...Band pass filter, 24...Tone detector, 25...Display device, 17...Clip circuit.

Claims (1)

[Claims] In a communication system that transmits information at the same time as a voice call by superimposing a low-level tone signal on the voice signal, the transmitting side can transmit the voice signal at a clip level set according to the dynamic range of the transmission path. An in-band tone transmission system characterized in that a clipping circuit is provided, and the tone signal is superimposed on an audio signal clipped by the clipping circuit and transmitted.