JPH06188849A - Multiplex transmitter - Google Patents

Abstract

PURPOSE:To provide a multiplex transmitter capable of multiplex transmitting sound and plural modulation signals simultaneously within the prescribed frequency band of a transmission line and also not damaging the clarity and intelligibility of sound. CONSTITUTION:The transmission band of the sound signals is set at a low frequency removal band (A) for which the intelligibility and the clarity are not damaged and at the same time, low frequency removal sound signals are synthesized with the first modulation signals (C) of a low frequency and the second modulation signals (B) of the frequency band at the intermediate part of the low frequency removal sound signals and are simultaneously transmitted. Also, since transmitted multiplex signals are separated respectively to the low frequency removal sound signals and the first and second modulation signals and demodulated, the clarity and the intelligibility of the sound are not damaged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multiplex transmission apparatus for simultaneously transmitting a plurality of modulated signals such as voice signals and digital data within a predetermined frequency band of a transmission line.

[0002]

2. Description of the Related Art Conventionally, in terminal equipment such as telephone lines,
A multiplex transmission system is known in which only one line is used to simultaneously transmit a low-frequency signal such as voice and measurement waveform data, and a plurality of signals such as digital data. For example, in wired or wireless communication, a voice signal and a modulation signal such as digital data can be simultaneously transmitted by a frequency division method. The frequency band of the wired transmission line is 0.3 to 3.4K for telephones.
When the voice and other modulated signals are multiplex-transmitted at a low frequency of Hz, the middle portion of the frequency band of the transmission path is divided and branched, and the voice signal is transmitted at a low frequency as shown in FIGS. 6 (A) and (B). A method of setting the modulation signal on the high frequency band side on the band side and a method of setting the voice signal on the high frequency band side and the modulation signal on the low frequency band side, as shown in FIG. 6C, are known. ing.

Also, a compound communication system for synthesizing and transmitting a voice signal and a signal other than the voice signal is a Japanese Patent Publication No. 55-2861.
No. 6 is disclosed. In this method, as shown in FIG. 7, a voice signal is transmitted in a low band and a high band of a transmission frequency band, and a transmission frequency band in which a center band component having a flat phase characteristic in which a voice signal is removed is removed is a facsimile data. It is used as a transmission band for signals other than voice.

[0004]

Speech is composed of vowels and consonants, and vowels have formants in the frequency band shown in FIG. For example, the first vowel "a"
Since the formant is around 0.3 KHz, if the transmission frequency band of voice is set to 0.3-2 KHz,
Since the second formant of the vowel "a" is 2.4 to 3 KHz, the transmitted voice may be lost. Also in the consonant, "sa", "shi", "su", "se",
The frequency range pronounced as "so" has a main component at 2 KHz or higher, so that the transmitted voice is lost, and there is a problem that the clarity and intelligibility of the voice are significantly deteriorated. Further, when two or more types of modulated signals are transmitted from a modem or the like as shown in FIG. 6B, the band of the voice signal is further narrowed, so that only one modulated signal is multiplexed and transmitted in addition to voice. Was the limit. Therefore, in the method in which the voice signal is transmitted only in the low frequency band or the high frequency band of the transmission frequency band, there is a problem that the intelligibility in the call is significantly deteriorated because the vowel and consonant components of the voice are lost.

Further, in the method disclosed in Japanese Patent Publication No. 55-28616, signals other than voice signals are transmitted using the central band of the transmission frequency band, but the clarity of voice is not impaired. The modulated signal that can be combined with the audio signal is
In reality, it is limited to one type. Furthermore, although a method is also used in which a voice signal in a voice band removed to transmit a signal other than voice is reproduced on the receiving side to improve intelligibility, there is a drawback that a very complicated circuit is required. there were.

An object of the present invention is to provide a multiplex transmission apparatus capable of simultaneously multiplex-transmitting voice and a plurality of modulated signals within a predetermined frequency band of a transmission line, and which does not impair the clarity and intelligibility of voice. Is.

[0007]

According to the present invention, there is provided transmission voice generation means for generating a low-frequency-removed voice signal in which low-frequency components of a voice signal are removed, and low frequency in a band of the removed low-frequency component. A first modulated signal generating means for generating a first modulated signal, a second modulated signal generating means for generating a second modulated signal in a frequency band of an intermediate portion of the low frequency band removed audio signal, It is configured by including a band-removed voice signal, a composite transmission unit that combines and transmits the first modulated signal and the second modulated signal.

Also, the present invention is a sound reproducing means for extracting and reproducing only a low-frequency-removed audio signal from which a low-frequency component has been removed from a multiplex transmission signal, and a band of the low-frequency component removed from the multiplex transmission signal. A first modulated signal reproducing means for extracting and reproducing only the first modulated signal set to the above, and only a second modulated signal set in a frequency band of an intermediate portion of the low frequency band removed audio signal from the multiplex transmission signal. And a second modulated signal reproducing means for taking out and reproducing.

[0009]

The transmission band of the audio signal is set to the low frequency band removing frequency band in which the intelligibility and the intelligibility are not deteriorated, and the low frequency band removing audio signal is the first modulated signal of the low frequency band and the low frequency band removing audio signal. Is synthesized with the second modulated signal in the frequency band of the middle part of the signal and transmitted at the same time. Further, since the transmitted multiplex signal is demodulated separately from the low frequency band removed voice signal and the first and second modulated signals, the clarity and intelligibility of the voice are not impaired.

[0010]

[Example] 0.3 to 3.4 KH used on a telephone line
audio that is multiplexed and transmitted in the z frequency band,
A frequency band of a modulated signal of digital data and a low frequency signal from a modem or the like will be described with reference to FIG. FIG. 1A shows an audio transmission frequency band, which is approximately 0.5 to 3.4K with the low frequency band 0.3 to 0.5KHz removed.
The low frequency rejection band of Hz is used. Figure 1 (B)
Indicates the frequency band of the modulated signal of the digital data transmitted from the modem, and two carrier frequencies f ₁ and f ₂ are used in this example. The modem transmission frequency band is within the voice transmission frequency band, and the carrier wave f has an amplitude such that the modulation signal of the modem is not interfered by the voice signal.
₁ and f ₂ are set. Also, as shown in FIG. 1C, a low-frequency signal or a low-speed signal such as a waveform signal from a measuring instrument or the like that is simultaneously transmitted has a frequency of 0.3 to 0.5 KHz including a carrier wave f _{3 of the} waveform signal, as shown in FIG. It is divided into frequency bands.

Next, the reason for distributing the voice signal and the modulated signals f ₁ , f ₂ and f ₃ as shown in FIG. 1 will be described. FIG. 2 shows the energy versus frequency of the speech signals generated by male and female speakers. As can be seen from the figure, the main component of the audio signal is 0.2
.About.0.5 KHz, and the amount of energy decreases as the frequency increases. Therefore, the amplitudes of the modulated signals f ₁ and f ₂ of the modem can be set to a level that does not interfere with the voice signal.

FIG. 3 shows the relationship between the cutoff frequency of the filter and the intelligibility of the voice. When the upper limit of the audio frequency is set to 1.5 KHz by the low-pass filter (LP), the intelligibility drops to 60%. , The intelligibility is 100 when the cutoff frequency of 0.5 KHz by the high-pass filter (HP) is set as the lower limit.
It just drops slightly from%. That is, FIG. 3 shows that sufficient clarity can be obtained by allocating the voice transmission frequency band to 0.5 to 3.4 KHz, and even if the low frequency component of the voice signal is removed, there is no problem in conversation. . Particularly, the high frequency band of the voice is important, and the voice and a plurality of modulated waves are simultaneously generated by setting the modulation signals f ₁ and f ₂ in the frequency band in which the formant is small, considering the relationship of the formants with FIG. Can be transmitted.

Furthermore, a low-frequency-removed voice signal and a plurality of modulated signals f ₁ , f ₂ and f synthesized for simultaneous transmission.
The demodulation of ₃ can be easily performed by the filter formed at the receiving end. The modulated signals f ₁ and f ₂ of the modem are taken out by a bandpass filter which passes only the component within the frequency band in which the signal components exist, and are restored to the original signals by the demodulator. Although the output side of this band pass filter includes a voice signal within the same band, there is no problem because the voice signal is synthesized with an amplitude that does not interfere with the modem. Further, the low-frequency modulated signal f ₃ can be restored by a low-pass filter and a demodulator like the modulated signal of the modem.

FIG. 4 shows the frequency characteristics of the received voice restoration filter in the frequency band near the carrier frequencies f ₁ and f ₂ . Digital data output from the modem "1" binary logic "0" is the frequency deviation modulation (FSK) in response to, sideband level of the carrier f _1, f ₂ generated at this time is FIG. 4 Since it is low as shown by the solid line, even if a part of the sideband in which the carriers f ₁ and f ₂ are removed by the filter for restoring the received voice shown by the broken line in the figure passes, the influence on the voice is extremely small. . Further, the voice restoration filter is composed of two narrow band elimination filters for eliminating the band for each of the carriers f ₁ and f ₂ to obtain the modulated signal f ₁
Since the voice signal component in the frequency band between −f ₂ can also be extracted as the reception signal, the influence on the intelligibility of the voice is extremely small. FIG. 5 is a block diagram showing an embodiment of the multiplex transmission apparatus of the present invention which realizes the above-mentioned principle. Figure 5
In the transmitting side, the audio signal converted into the electric signal by the microphone 1 is amplified by the amplifier 2, and the audio signal of 0.5 KHz or less is cut off by the high-pass filter (HPF) 3. Next, the low-pass filter (LPF) 4 blocks the frequency band of 3.4 KHz or more, and as a result, the audio signal from which the low frequency band in the audio transmission band shown in FIG. Entered in.

A low-frequency signal such as a measurement waveform or a low-speed transmission waveform is input from a measuring instrument to a voltage / frequency (V / F) converter 6, where it is modulated to a frequency corresponding to a voltage level and is converted into a high frequency range. The signals are sequentially sent to the filter 7 and the low pass filter 8. A low-frequency signal that passes through the frequency band of 0.3 to 0.5 KHz as shown in FIG. 1C in the high-pass filter 7 and the low-pass filter 8 is input to the adder 5.

Digital data from the measuring instrument is CP
U9, whose output is frequency shift keying (FSK)
Modulated by the circuit 10, the modulated output is sequentially sent to the high-pass filter 11 and the low-pass filter 12, and is shown in FIG.
The modulated signal that has passed the frequency band shown in is input to the adder 5.

The adder 5 adds a voice signal in a limited frequency band through each filter, a modulation signal corresponding to digital data from a modem, a low frequency signal such as a measured waveform, and multiplexes them, and at the same time, the hybrid circuit 13 , Is transmitted via the transmission line 14 including a telephone line.

On the receiving side, the multiplexed signal sent via the transmission line 14 is received via the hybrid circuit 15, and the voice signal is subjected to the high-pass filter 16, the band-pass stop filters (BEF) 17 and 18, and the low-pass filter. Only the audio signal is selected through the filter 19, amplified through the amplifier 20 in sequence, and then output from the speaker 21 as audio. Further, the low frequency modulation signal f ₃ is supplied to the high pass filter 22 and the low pass filter 2
Only the low frequency signal is selected through 3 sequentially and demodulated into a voltage waveform by the frequency / voltage (F / V) converter 24. Further, the received multiplexed signal is sequentially passed through a high-pass filter 25 and a low-pass filter 26 to select only the modulation signals f ₁ and f _{2 of} the modem corresponding to the digital data, and the frequency shift demodulation circuit 27 discriminates the digital data. CPU28
The digital data is output via.

As described above, the three kinds of signals of the voice, the digital data and the waveform signal sent from the transmitting side are simultaneously multiplexed by frequency division and sent to the receiving side via the transmission line 14 and are classified by the receiving side. And is demodulated. As described with reference to FIGS. 1 to 4, since a specific transmission frequency band is set depending on the type of signals to be multiplexed, low frequency signals and digital data may be lost,
Also, the intelligibility and intelligibility of the voice will not be impaired.

Note that the multiplex transmission apparatus of the present invention is not limited to the configuration of FIG. 5, and various modifications can be made as long as they satisfy the gist of the present invention described with reference to FIGS. Is.

[0021]

According to the present invention, a plurality of types of signals including voice can be multiplex-transmitted within a limited frequency band of a transmission line without impairing the intelligibility and intelligibility of the voice. By comparison, the transmission of voice can be improved and two types of modulated signals other than voice can be multiplexed. Further, since the multiplex transmission signal can be restored to the voice signal and the modulated signal respectively, and the voice signal component of the frequency band of the modem modulated signal can also be restored as the reception signal, the influence on the intelligibility of the voice is extremely small. Also, the circuit configuration of the multiplex transmission device is simple and can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a diagram for explaining distribution of transmission frequency bands of voice and various signals according to the present invention.

FIG. 2 is a diagram showing a relationship between a speaker's vocal energy and frequency.

FIG. 3 is a diagram showing a relationship between a cutoff frequency of a filter and voice clarity.

FIG. 4 is a diagram showing filter characteristics of received voice restoration in a frequency band near the modulation frequency of the modem of the present invention.

FIG. 5 is a block diagram showing an embodiment of a multiplex transmission device of the present invention.

FIG. 6 is a diagram showing distribution of transmission frequency bands of conventional audio signals and modulated signals.

FIG. 7 is a diagram showing another distribution of transmission bands of conventional audio signals and modulated signals.

FIG. 8 is a diagram showing the distribution of formants of vowels.

[Explanation of symbols]

3,7,11,16,22,25 High-pass filter 4,8,12,19,23,26 Low-pass filter 17,18 Bandpass stop filter 5 Adder 13,15 Hybrid circuit 14 Transmission line

Claims (3)

[Claims] 1. A transmission apparatus that multiplex-transmits a voice signal and a modulated signal within a predetermined transmission frequency band of a transmission path, wherein a transmission voice generation unit generates a low-frequency-removed voice signal from which a low-frequency component of the voice signal has been removed. A first modulation signal generating means for generating a low frequency first modulation signal in the band of the removed low frequency component, and a second modulation in a frequency band of an intermediate portion of the low frequency removed audio signal. A second modulation signal generating means for generating a signal, and a synthetic transmission means for synthesizing and transmitting the low-frequency-removed audio signal, the first modulation signal, and the second modulation signal. Multiplexing device. 2. A multiplex transmission device for demodulating a multiplex transmission signal including a voice signal and a modulation signal multiplexed within a predetermined transmission frequency band of a transmission line, wherein a low frequency component is removed from the multiplex transmission signal. Sound reproduction means for extracting and reproducing only the low-frequency removed sound signal, and a first modulated signal for extracting and reproducing only the first modulated signal set in the band of the removed low-frequency component from the multiplex transmission signal Reproduction means, and second modulation signal reproduction means for extracting and reproducing only the second modulation signal set in the frequency band of the intermediate portion of the low-frequency-removed audio signal from the multiplex transmission signal. And multiplex transmission equipment. 3. The multiplex transmission device according to claim 1, wherein the second modulation signal is a signal obtained by frequency shift modulating digital data.