JPS6384216A - Voice/data multiplexer - Google Patents

Abstract

PURPOSE:To suppress the noise component in a modulation carrier mixed in a voice signal band by providing a filter circuit having a prescribed transmitting characteristic to a voice signal output path of a frequency division multiplex signal converted into an electric signal by an acoustic coupler. CONSTITUTION:A filter circuit 21 is provided between a speaker 20 and a voice signal reception circuit BEF 19. The noise component caused by a modulation carrier passing through a handset 3 comprising a carbon microphone is distributed mainly in the voice band adjacent to the band of modulation carrier and a low frequency band by a band of the modulation carrier from a frequency OHz. Thus, the characteristic of the circuit 21 is set in response to the distribution of the noise component. As a result, even if a frequency multiplex signal including noise component in the voice band is sent as a side tone via a telephone set, the noise component is suppressed by the circuit 21 and sent from the speaker 20, then the noise level sent in mixing with the received voice is less and high quality talking is attained.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Field of Application) The present invention is a system for transmitting voice signals by combining data and voice frequency division multiplexed signals with a telephone handset using an acoustic cube. -Regarding improvements to data multiplexing equipment.

(Prior art) In recent years, a method has been developed that simultaneously transmits graphic data and audio signals input by hand using a tablet input device using a telephone line, but this type of method uses frequency modulation of a carrier wave by data. The carrier wave and the audio signal are frequency division multiplexed and transmitted as shown in FIG. 6, for example. FIG. 7 shows an example of the configuration of a voice/data multiplexing apparatus for implementing this type of transmission system, where 1 indicates a telephone connected to the telephone line 2, and 3 indicates its handset. This device frequency modulates a carrier wave using input data DT in a frequency modulation circuit 11, limits the band of this modulated carrier wave in a band pass filter (BPF) 12, converts audio VC into an audio signal with a microphone 13, and then performs band elimination. filter(
BEF) 14 attenuates the modulated carrier wave band, and an adder 15 synthesizes these modulated carrier waves and the audio signal, which is then electro-acoustic converted by the speaker 16a of the acoustic coupler 16 and input to the speaker of the handset 3. , is sent from telephone 1 to telephone line 2. On the other hand, the frequency division multiplexed signal that has arrived via the telephone line 2 is acoustic-to-electrically converted by the microphone 16b of the acoustic coupler 16 from the receiver of the handset 3, and the frequency division multiplexed signal is introduced into the BPF17.
and BEF 19, the modulated carrier wave band is separated and extracted by BPF1 7, and then demodulated by frequency demodulation circuit 18 to reproduce the data and output to a monitor device or the like. Further, the BEF 19 separates and extracts the audio signal component from the frequency division multiplexed signal, and the audio signal is sent out as audio from the monitor speaker 20. If such a device is used, simultaneous transmission of voice and data can be performed relatively easily by using an existing telephone, and for example, it is possible to transmit solid information such as a map while talking.

However, such conventional devices have the following problems. In other words, the carrier wave modulated by data in the frequency modulation circuit 11 changes its carrier frequency as the data changes, and is output as a modulated carrier wave containing various frequency components at the point of change in the carrier frequency. For this reason, B
The PFl 2 outputs a modulated carrier wave whose frequency is fully spread in its passband, and this modulated carrier wave is synthesized with the audio signal by the adder 15, and then converted into an audible sound by the acoustic coupler 16, which is transmitted to the handset 3. It will be input into the transmitter. Carbon microphones, which do not require signal amplification means, are generally used in telephone transmitters, but when audible sound with a modulated carrier wave as described above is input to this carbon microphone, second-order distortion occurs. A frequency multiplexed signal in which a noise component is superimposed on the audio signal band is then transmitted. Then, when the frequency multiplexed signal containing this noise is transmitted as sidetone from the receiver to the receiver circuit side via the telephone 1fi1, the noise component is not removed by the BEF 19, so the noise is output as is from the speaker 20, and the receiver receives the call. This will impede the ability to hear audio. This is particularly undesirable because it becomes a problem when the quality of the call is poor, such as when the line loss in the communication path is large, and in some cases it becomes impossible to make a call.

(Problems to be Solved by the Invention) As described above, in the conventional device, the noise component from the modulated carrier wave generated when passing through the transmitter of the telephone is directly output from the speaker of the receiver circuit as sidetone. Therefore, there is a problem in that the listening of the received voice is obstructed and the quality of the call is deteriorated.The present invention focuses on this point, and the noise component of the modulated carrier wave mixed into the voice signal band is directly transmitted to the receiving circuit system. The present invention aims to provide a voice/data multiplexing device that can improve the quality of calls by reducing the S/N ratio of received voices by preventing them from being output from speakers.

[Structure of the Invention] (Means for Solving the Problems) As shown in FIG.
A filter circuit 100 having predetermined pass characteristics is provided, and the filter circuit 100 suppresses noise components caused by modulated carrier waves generated in the audio signal band.

(Function) As a result, even if a frequency multiplexed signal containing a noise component in the voice band is transmitted as sidetone through the telephone, the noise component is suppressed by the filter circuit 100 and sent out from the speaker, so it is mixed into the received voice. As a result, even if the line quality is poor, the quality of the received voice is sufficiently ensured and high-quality calls are possible (Example) Figure 2 shows the present invention. 1 shows the configuration of an audio/data multiplexing device in an embodiment of the present invention. In this figure, the same parts as those in FIG. 7 are given the same reference numerals and detailed explanations will be omitted.

A filter circuit 21 is provided between the BEF 19 of the audio signal reception circuit and the speaker 20.

This filter circuit 21 is composed of a band elimination filter having a predetermined attenuation range in the audio band. By the way, the noise component generated when the modulated carrier wave passes through the transmitter of the handset 3 made of a carbon microphone is as follows.
For example, as shown in FIG. 3, there is a voice band i adjacent to the band f0 of the modulated carrier wave.

It is mainly distributed in a low frequency band of 10 minutes from the frequency OHz to the band of the variable vA carrier wave. Therefore, the pass characteristic of the filter circuit 21 is set, for example, as shown in FIG. 4, depending on the distribution of this noise component.

With such a configuration, the frequency multiplexed signal returned as sidetone from the telephone tll during a call is first removed at 8EF'19 to separate and extract the voice signal, and then introduced into the filter circuit 21. , this filter circuit 21
further controls the passband. Here, as shown in FIG. 4, the pass characteristic of this filter circuit 21 is such that the amount of pass attenuation of the noise generation band by the modulated carrier wave is set to be large. Noise components due to variable FJ4m transmission are suppressed. Therefore, the speaker 20 outputs sidetone and received sound that are less affected by the noise component. FIG. 5B shows the frequency characteristics of the audio signal after passing through the filter circuit 21, and the level of the noise component is significantly reduced compared to characteristic A when the audio signal does not pass through the filter circuit 21.

Note that by passing through the filter circuit 21, in addition to the noise components, some bands of the received voice and sidetone are attenuated, but the voice signals of the received voice and sidetone are attenuated throughout the entire audible frequency band. Since the signal is distributed at the ^ level, even if it is partially attenuated by the filter circuit 21, it hardly affects the communication.

As described above, in this embodiment, the filter circuit 21 is provided in the voice reception path, and the filter circuit 21 suppresses the noise component due to the change in the frequency multiplexed signal transmitted as sidetone [R transmission]. Therefore, the noise level output from the Skuichiriki 20 is significantly reduced, and as a result, the S/N of the received voice improves, making it possible to improve the call quality, especially when making a call in a state where the call path quality is poor. It is possible to hear the received voice clearly even in the case of

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, a filter circuit is provided between the BEF 19 and the speaker 20 in the voice receiving path, but the BPF1
7 and the branch point to BEF19 and the above-mentioned BEF19. In addition, the configuration, pass characteristics, etc. of the filter circuit can be modified in various ways without departing from the gist of the present invention.

[Effects of the Invention] As detailed above, according to the present invention, a filter circuit having a predetermined pass characteristic is provided in the audio signal output path of the frequency division multiplexed signal converted into an electric signal by the acoustic coupler,
By suppressing the noise component due to the modulated carrier wave generated in the audio signal band by this filter circuit, it is possible to prevent the noise component of the modulated carrier wave mixed into the audio signal band from being output as is from the speaker of the receiving circuit system. As a result, it is possible to provide a voice/data multiplexing device that can reduce the S/N of received voice and improve call quality.

[Brief explanation of the drawing]

FIG. 1 is an Akebono block diagram for explaining the present invention in detail, and FIGS. 2 to 5 are audio and
This is to explain the data multiplexing device. Fig. 2 is a circuit block diagram showing the configuration of the device, Fig. 3 is a frequency characteristic diagram showing the noise generation distribution, and Fig. 4 shows the pass characteristics of the filter circuit. FIG. 5 is a frequency characteristic diagram of an audio signal to explain the effect, FIG. 6 is a frequency characteristic diagram showing the state of frequency division multiplexing of a modulated carrier wave by audio and data, and FIG.
The figure is a circuit block diagram showing the configuration of a conventional audio/data multiplexing device. 100...Filter circuit, 1...Telephone, 2...
Telephone line, 3...Handset, 11...Frequency modulation circuit, 12.17...Band pass filter (BPF)
), 13... Microphone, 14.19... Band elimination filter (BEF), 15... Adder,
16...Acoustic coupler, 16a...Speaker, 16b
... Microphone, 18 ... Frequency demodulation circuit, 20
...monitor speaker, 21...filter circuit. Applicant's representative Patent attorney Takehiko Suzue Shu 3 losses (Hz) Figure 3 lap a number mountain 2] Shu 3 losses [ce] Figure 5 Frequency (Hz)

Claims (1)

[Claims] After frequency-division multiplexing the carrier wave frequency-modulated by the data and the voice signal, the signal is coupled to the handset of the telephone via an acoustic coupler and sent out to the telephone line, and the frequency-division multiplexed signal arriving via the telephone line is transmitted to the above-mentioned acoustic In an audio/data multiplexing device that converts the signal into an electrical signal using a coupler and then separates it into an audio signal and a modulated carrier wave and outputs each, the audio A voice/data multiplexing device characterized by being provided with a filter circuit that suppresses noise components due to modulated carrier waves generated in a signal band.