JP2000244949A - Dtmf signal transmitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To transmit a DTMF signal without generating an error even when delay time is shortened on the transmitting side by comparing an output from a DTMF character extraction part with an output from a receiving side DTMF detection part, selectively switching either one of an output from a decoder processing part and an output from a DTMF generation part and shortening the delay time of a transmitting side DTMF detection processing part. SOLUTION: Relating to the transmitting device, a DTMF character extraction part 14 in a receiving side codec processing part 13 extracts a DTMF character superposed to compressed sound data from arriving encoded data. A DTMF generation part 7 generates a PCM code of a DTMF signal based on an output from the extraction part 14. A decoder processing part 6 receives only the compressed sound data from the extraction part 14 and extends the received data. A comparing part 16 mutually compares outputs from a 2nd DTMF detection part 15 and the extraction part 14 and outputs a switching control signal to a switching part 17 based on a selection control table.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DTMF signal transmission device, and more particularly, to a delay generated for DTMF detection in a codec processing unit on a transmission side which converts a voice band signal into a low bit rate digital signal and transmits the digital signal. Means for reducing time. Note that the low bit rate here refers to a bit rate of 1/8 or less of 64 kbps when encoding a voice band signal based on the sampling theorem.

[0002]

2. Description of the Related Art DTMF (dual tone multi frequenc)
y) The signal is generally a tone dial signal generated by pressing a push button of a telephone, and is a combination of two frequencies in a voice frequency band. In recent years, it has been frequently used not only for connection of a line but also for selection signals of numbers / symbols of various interactive automatic services after a telephone line is established. The frequency configuration used for the DTMF is set so as to avoid harmonic relations that frequently appear in music and voices, so that the DTMF receiver is less likely to malfunction due to speech voices other than DTMF signals. In recent years, digitalization of communication systems has progressed. For example, DSU (Di
In a transmission device having a digital service unit (GI) function, an analog signal from a terminal such as a telephone or a facsimile accommodated by the transmission device is converted to a PCM (Pulse Code Modulator) in order to increase line efficiency.
In addition to digitalization by means of ION), the digitally compressed data is transmitted at a low bit rate. There are various types of digital compression technology. Among them, the one that achieves a high compression ratio removes information components of low importance by focusing on human characteristics, and performs correlation before and after signals. To make predictions. When such a digital compression technique is used, humans can recognize voice information with almost no deterioration in voice quality. However, when a DTMF signal is transmitted and received between analog terminal devices, processing between mechanical devices is general, and the analog signal waveform restored on the receiving side after the above-described high-compression digital compression / expansion conversion is performed. May greatly change with respect to the DTMF original signal waveform on the transmission side, and the DTMF receiver may malfunction.

In order to improve this, conventionally, in a transmission device on the transmission side, a digital signal (DT) has been obtained before digitally compressing an audio signal.
Some MF signals are detected and transmitted as a character (predetermined code string) signal associated with the DTMF signal, and some transmission devices on the receiving side detect the character signal and generate a DTMF signal. FIG. 4A is a diagram illustrating a configuration example of a transmission-side codec processing unit of a conventional DTMF signal transmission device, and FIG. 4B is a configuration example of a reception-side codec processing unit of a conventional DTMF signal transmission device. FIG. It should be noted that a configuration for performing one-way communication is shown for simplicity of description. The transmission-side codec processing unit 1 of the DTMF signal transmission apparatus shown in the example of FIG. 4A converts an analog signal from an analog terminal into an A / D (analog /
Digital data is input by a (digital) converter into a digital signal.
It is distributed and input to the DTMF detector 3. The output of the coder processing unit 2 and the output of the DTMF detection unit 3 are connected to a switch 4, and the output of the switch 4 is transmitted as encoded data.

[0004] The transmitting-side codec processing section 1 of the DTMF signal transmission apparatus shown in FIG. 1 functions as follows. That is,
The coder processing unit 2 converts audio data, which is an uncompressed digital signal (for example, in a PCM code state), into, for example, ITU-
T Recommendation G. 729 CS-ACELP (Conjuga
te Structure and Algebrai
c Code-Excited Linear Pre
The DTMF detection unit 3 detects a DTMF signal from the audio data by performing a frequency analysis using, for example, a Goertzel algorithm or the like, and detects the DTMF signal. When this is done, it is converted into a character signal corresponding to the type of the DTMF signal and output. The combination of DTMF signals used here is
Assuming that there are 16 types of four frequencies in the high group and four types in the low group, the character signal is 4 bits. Then, when there is an output from the DTMF detection unit 3, the switching unit 4 switches the contacts so as to select the output of the DTMF detection unit 3 and sends the character signal as encoded data to the receiving side. When there is no output from 3, the contact is switched so as to select the output of the coder processing unit 2, and the compressed audio data is transmitted to the receiving side as encoded data.

[0005] The receiving side codec processing section 5 of the DTMF signal transmission apparatus shown in the example of FIG. 4 (b) distributes the coded data to be input to the decoder processing section 6 and the DTMF generating section 7, and the switching section 8 Is the output of the decoder processing unit 6 and the DTMF
One of the outputs of the generator 7 is selected and output as audio data.

[0006] The receiving side codec processing section 5 of the DTMF signal transmission apparatus shown in FIG. 1 functions as follows. That is,
The decoder processing section 6 expands the coded data and inversely converts the data into audio data. The DTMF generating section 7 detects a character signal from the coded data, and a DTMF signal in a PCM state corresponding to the character signal. Is to occur. When a character signal is detected by the DTMF generator 7, the switch 8 switches the DTMF generator 7.
The output of the decoder processing unit 6 is selected and output at other times.

[0007] The form of the signal transmitted at this time will be described. FIG. 5 shows an example of the form of a transmission / reception signal of a conventional DTMF signal transmission apparatus. One frame consists of 80 bits, and FIG. 5A shows a case where the output of the coder processing unit 2 is selected. FIG. 5B shows a case where the output of the DTMF generator 7 is selected. That is, in both figures, a frame identification bit is added to the head of the frame, and in this case, 5 bits are allocated. FIG. 5A shows voice data compressed to the remaining 75 bits, and FIG. 5B shows four bits of a character signal after a frame identification bit, and the remaining 71 bits are pseudo data in advance. It has a configuration in which a predetermined code string is mounted.

As described above, by observing the frame identification bits on the receiving side, the transmitting side can determine which of the output signals from the coder processing section 2 or the DTMF detecting section 3 is present. Or D by the switching unit 8
TMF can be switched and output.

[0009]

However, the above-mentioned conventional DTMF signal transmission device has the following problems. That is, the time required for digital compression encoding in the coder processing unit 2 on the transmission side is 10 m.
s, while DT in the DTMF detector 3
The time required for MF signal detection takes about 40 ms. Accordingly, it is necessary to delay the output from the coder processing unit 2 by about 30 ms and transmit the encoded data, and the transmitted encoded data has a delay time of about 40 ms. If the sample time of the DTMF detection unit 3 is shortened, the required time can be reduced to 10 ms. However, if the sample time is shortened, the probability of erroneously detecting a voice signal as a DTMF signal increases.
There was a problem that MF tone could be heard. Further, if the delay time is long, there is a problem that not only a sense of incongruity occurs in the response between the callers during a call but also the processing load becomes heavy when using the online time adjustment function or the echo cancel function.

The present invention has been made to solve such a problem, and a DT that can transmit a DTMF signal without error even if the delay time on the transmission side is reduced.
An object is to provide an MF signal transmission device.

[0011]

SUMMARY OF THE INVENTION In order to solve the above problems, a DTMF signal transmitting apparatus according to the present invention is a communication apparatus for transmitting a voice band signal at a low bit rate, and a transmitting apparatus transmits voice data. A coder processing unit that performs digital compression encoding, and a DTMF (dual tone mult)
i) a transmitting DTMF detecting section for detecting a signal, and a superimposing section for superimposing a DTMF character signal on the encoded data digitally compressed and encoded by the coder processing section based on the output from the DTMF detecting section. The receiving-side device performs DTM from the received encoded data.
A DTMF character extraction unit for extracting an F character signal, a decoder processing unit for digitally expanding and decoding encoded data, a receiving DTMF detection unit for detecting a DTMF signal from an output of the decoder processing unit, and a DTMF character extraction unit A DTMF generating unit that generates a DTMF signal based on an output from the DTMF character extracting unit, a comparing unit that compares an output of the DTMF character extracting unit with an output of the receiving-side DTMF detecting unit, A switching unit for selectively switching one of the output of the decoder processing unit and the output of the DTMF generation unit, wherein the delay time of the transmission-side DTMF detection processing unit is reduced.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on illustrated embodiments. FIG. 1 is a functional block diagram showing an embodiment of a DTMF signal transmission apparatus according to the present invention. FIG. 1A is a diagram illustrating a configuration example of a transmission-side codec processing unit, and FIG. 1B is a diagram illustrating a configuration example of a reception-side codec processing unit.

The transmission side codec processing unit 10 of the DTMF signal transmission apparatus shown in the example of FIG.
And a first DTMF detection unit 11 and a superimposition processing unit 12. The audio data input to the transmission-side codec processing unit 10 is in a PCM code state, which is the coder processing unit 2 and the first DTMF The distribution is provided to the detection unit. Then, the output from the coder processing unit 2 and the first DT
The output of the MF detection unit 11 is connected to the superimposition processing unit 12, and the output of the superimposition processing unit 12 is transmitted to the receiving side as encoded data.

The transmitting codec processing section 10 of the DTMF signal transmitting apparatus shown in FIG. 1 functions as follows. That is, the coder processing unit 2 converts voice data, which is an uncompressed digital signal, into a compressed digital signal as in the case of the conventional one, and the first DTMF detection unit 11 has the same configuration as the conventional one. When a DTMF signal is detected, a corresponding character signal is output. However, the sample time is reduced to 10 ms, which is the same as the processing time of the coder processing unit 2. Then, the superimposition processing section 12 superimposes the output of the first DTMF detection section 11 on the output signal of the coder processing section 2 and sends out the coded data to the receiving side as encoded data.

Here, the above-described superimposition processing will be described with reference to the drawings. FIG. 2 is a diagram showing an example of a form of a transmission / reception signal of the DTMF signal transmission device according to the present invention. In the signal form shown in this example, one frame is composed of 80 bits, and one flag bit is added to the head of the frame. For example, when the first DTMF detection unit detects a DTMF signal, the flag bit is set to "1", and a character signal is assigned bit by bit to 20, 40, 60, and 80 bit positions from the head bit of the frame. go. That is, a 4-bit character signal is dispersedly embedded in one frame and transmitted together with the compressed digital audio signal. When the DTMF signal is not detected, the flag bit is set to "0" and only the compressed digital audio signal is transmitted.

Next, the receiving-side codec processing unit 13 of the DTMF signal transmission apparatus shown in the example of FIG. 1B receives a DTMF character extracting unit 14 which receives the input encoded data.
A decoder processing unit 6 which receives compressed audio data from which the DTMF characters have been removed from the DTMF character extraction unit 14 as input, and a second DTMF detection unit 15 which receives expanded audio data from the decoder processing unit 6 as input.
A comparison unit 16 to which the output of the detection result from the second DTMF detection unit 15 and the output of the extraction result from the DTMF character extraction unit 14 are input, and the extraction result from the DTMF character extraction unit 14 D with output as input
A TMF generating unit 7 and a switching unit 17 that switches between the output of the decoder processing unit 6 and the output of the DTMF generating unit 7 based on the output of the comparing unit 16 and outputs the data as audio data.

The receiving-side codec processing unit 13 of the DTMF signal transmission apparatus shown in FIG. 1 functions as follows. That is, the DTMF character extraction unit 14 extracts a DTMF character superimposed on the compressed voice data as shown in FIG. Specifically, the flag bit at the head of the frame is monitored, and if "1", the code at the bit position of 20, 40, 60, 80 of the frame is extracted and recognized as a 4-bit DTMF character. DTMF type information
It is supplied to the generator 7 and one input of the comparator 16. DT
The MF generator 7 generates a PCM code of the DTMF signal based on the output from the DTMF character extractor 14. The decoder processing unit 6 receives only the compressed audio data from the DTMF character extraction unit 14 and performs an inverse conversion so as to decompress it. The second DTMF detection unit 15 receives the audio data expanded by the decoder processing unit 6, detects a DTMF signal from the audio data, and supplies the result to one input of the comparison unit 10. The comparison unit 16 compares the output of the second DTMF detection unit 15 with the output of the DTMF character extraction unit 14, and outputs a switching control signal to the switching unit 17 based on the selection control table shown in FIG.

FIG. 3 shows a switching control table of the switching unit in the receiving codec processing unit of the DTMF signal transmission apparatus according to the present invention. First, the DTMF character extraction unit 1
4 is “voice” and the second DTMF detector 15
Is "sound", the comparing unit 16 outputs a control signal to the switching unit 17 so as to select the output of the decoder processing unit 6. Next, the DTMF character extraction unit 1
4 is “DTMF” and the output result of the second DTMF detection unit 15 is “voice”, the comparison unit 16
Outputs a control signal to the switching unit 17 so as to select the output of the decoder processing unit 6. Next, when the output result of the DTMF character extraction unit 14 is “voice” and the output result of the second DTMF detection unit 15 is “DTMF”, the comparison unit 16 sends the output of the decoder processing unit 6 to the switching unit 17. Output a control signal to select. Next, the output result of the DTMF character extraction unit 14 is “DTMF” and the second DTMF
When the output result of the F detection unit 15 is “DTMF”, the comparison unit 16 outputs a control signal to the switching unit 17 so as to select the output of the DTMF generation unit 7. That is, the switching process is performed with priority given to the detection result of the second DTMF detection unit 15.

At the receiving side, the DTMF signal is detected again from the decoded signal, and the DTM at the transmitting side is detected.
By comparing with the TMF detection result, the DT on the transmitting side is obtained.
It is possible to compensate for a decrease in detection accuracy due to a reduction in the MF detection time. In other words, when the result does not match in the comparing unit 16, it is determined that there is an error in the DTMF detection on the transmitting side, and a signal is output from the decoder processing unit 6 as a voice. , The DTMF signal generated by the DTMF generating unit 7 is selected by the switching unit 17 so that the DTMF signal is free from distortion due to transmission.
An MF signal can be output.

In the embodiment of the present invention described above, an example has been described in which the audio data is a PCM code, that is, an uncompressed digital signal. However, the present invention is not limited to this example. For example, the coder processing unit 2 on the transmission side and the first DTMF detection unit, and the second D
An A / D converter may be provided for the TMF detection unit 15 and a D / A converter may be provided for the decoder processing unit 6 and the DTMF generation unit 7 on the receiving side so that audio data is converted into an analog signal.

[0021]

As described above, the DTMF according to the present invention is
The signal transmission device reduces the time required for DTMF detection on the transmitting side to about the same as the time required for coder processing,
The DTMF character is superimposed on the compressed audio data and transmitted, and the DTMF is detected from the decompressed audio data on the receiving side and compared with the DTMF detection result on the transmitting side to compensate for the decrease in the DTMF detection accuracy on the transmitting side. With this configuration, the DTMF signal can be transmitted without error even if the delay time due to the detection of the DTMF signal on the transmission side is reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of a DTMF signal transmission device according to the present invention.

FIG. 2 is a diagram showing a signal form example of a transmission signal according to the present invention.

FIG. 3 is a diagram showing a switching control table according to the present invention.

FIG. 4 is a block diagram showing a configuration example of a conventional DTMF signal transmission device.

FIG. 5 is a diagram showing an example of a signal form of a transmission signal in the related art.

[Explanation of symbols]

 1, 10 ... codec processing section on transmission side 2 ... coder processing section 3 ... DTMF detection section 4, 8, 17 ... switching section 5, 13 ... codec processing section on reception side 6. ..Decoder processing unit 7: DTMF generation unit 11: first DTMF detection unit 12: superimposition processing unit 14: DTMF character extraction unit 15: second DTMF detection unit 16・ Comparison section

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (1)

[Claims] 1. A communication device for transmitting a voice band signal at a low bit rate, comprising: a coder processing unit for digitally compressing and coding voice data;
A transmitting-side DTMF detecting unit that detects a dual tone multi-frequency (TMF) signal; and a superimposing unit that superimposes a DTMF character signal on the encoded data digitally compressed and encoded by the coder processing unit based on an output from the DTMF detecting unit. And a DT for extracting a DTMF character signal from the received encoded data.
An MF character extracting unit, a decoder processing unit for digitally expanding and decoding the encoded data, a receiving DTMF detecting unit for detecting a DTMF signal from an output of the decoder processing unit, and an output from the DTMF character extracting unit. A DTMF generator for generating a DTMF signal;
A comparing section for comparing the output of the MF character extracting section with the output of the receiving side DTMF detecting section, and the output of the decoder processing section or the DTMF based on the output from the comparing section.
A DTMF signal transmission device comprising: a switching unit that selectively switches one of the outputs of an F generation unit.