JPH0837504A - Predictive coded audio signal receiver - Google Patents

Abstract

PURPOSE:To suppress clicking noise caused by code replacement for suppressing clicking noise based on transmission line error. CONSTITUTION:When the transmission line error is detected by an error detecting part 15, a gate signal for the length from 3 to 5 packets from the packet just after that error is generated by a gate signal generating part 21, and the clicking noise in the output of an ADPCM decoder 13 is detected by a detecting part 22. That detected output and the gate signal are ANDed by a circuit 23, a holding circuit 24 is set by that output rising, and a suppressing signal is generated up to the end of the packet at that time. Corresponding to the suppressing signal, an ADPCM decoded output is suppressed by a suppressing processing part 25 and supplied to a PCM decoder 44.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention decodes a predictive-coded voice signal such as ADPCM coding into an analog signal, and in particular, a predictive-coded voice signal considering improvement of voice quality deterioration due to a transmission path error. Regarding the receiver.

[0002]

2. Description of the Related Art A coded speech signal sequence including an error is ADP
When input to the CM decoder, the states of the adaptive predictor and the scale factor adaptation unit inside the decoder are different from those on the encoder side due to an erroneous code. As a result, the output waveform from the decoder is different from the input voice waveform to the encoder, which causes click noise and deteriorates the voice quality. Code replacement is a conventional method for improving such deterioration of voice quality. The code replacement method will be described below with reference to FIG. The 32 kb / s received ADPCM coded voice signal 11 is supplied to the ADPCM decoder 13 through the code replacement processing section 12, converted into a 64 kb / s PCM code, and the PCM code is converted into an analog section signal by the PCM decoder 14. It But CR
When an error is detected by the error detection unit 15 such as the C error detection, the AD in the packet is detected for the packet.
The code replacement processing unit 12 performs code replacement on the received ADPCM code voice signal so as to limit the possible values of the PCM code. There may be various patterns in this replacement pattern, for example, "100" which is a code representing the maximum difference.
A general pattern is to replace “0” and “0111” with “1111”, which is a code indicating no difference.The signal after this replacement processing is performed by the ADPCM decoder 13
By inputting into, the change in the voice signal after decoding is limited, so that click noise caused by a sudden change in amplitude is reduced. Therefore, at least immediately before the packet corresponding to the code replacement processing unit 12 is input, the error detection unit 15 detects whether or not the packet has an error.

[0003]

In the conventional ADPCM voice signal quality improving system for transmission line errors described above, the internal state of the ADPCM decoder 13 does not match the internal state of the encoder side immediately after the end of error detection. Even if the ADPCM signal input to the ADPCM decoder 13 has no error, A
Click noise can be generated from the DPCM decoder. SUMMARY OF THE INVENTION It is an object of the present invention to solve this problem and to provide a predictive coded voice signal receiver such as ADPCM which can improve the quality of output voice particularly for errors which occur in bursts.

[0004]

According to the first aspect of the present invention, click noise is detected from the decoded output of the predictive code decoder by the click noise detecting means, and the detection results in the decoded signal from the predictive code decoder. Is suppressed by the suppression means.
According to the second aspect of the invention, the suppression of the suppression means is performed when the gate signal is generated by the gate signal generation means by the signal in which the transmission path error is detected and the click noise is detected in the gate signal. From then to the end of the packet at that time, a suppression signal is generated, and this is done.

According to the third aspect of the invention, in the suppression of the suppressing means, the gate signal is generated by the gate signal generating means by the signal in which the transmission path error is detected, and the pulse is generated by the click noise detecting means. Is performed by the logical product output of the pulse and the gate signal. In the invention of any one of claims 2 and 3, the gate signal is generated only when a replacement for a specific code is performed.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the invention of claim 2, and FIG.
The same symbols are attached to the portions corresponding to. Error detector 1
5, it is checked whether or not there is an error in the received ADPCM code by using a cyclic code (CRC code) for each packet having an appropriate code length, for example, 160 bits, and if an error is detected,
As in the conventional case, the code replacement processing unit 12 replaces a specific code, for example, "1000" or "0111", in the packet with "1111". In the present invention, the gate signal generation unit 21 is driven by the error detection output signal indicating that an error is further detected, and the gate signal generation unit 21 generates the gate signal immediately after the packet in which the error detection signal is generated. Error-free ADP after the code replacement
When the CM signal is received, the internal state of the ADPCM decoder 13 is restored to a normal state, that is, the time until it becomes equal to the internal state of the encoder. Need about 5 Therefore, the length of the gate signal generated by the gate generator 21 is 3 to 5
It is assumed to be the packet length.

In the present invention, the click noise in the decoded output from the ADPCM decoder 13 is detected by the click noise detector 22. The click noise detection unit 22 measures the absolute value of the amplitude difference between adjacent PCM codes output from the decoder 13 and determines that the noise is click noise if the measured value is larger than the threshold value. For example, a PCM coded signal equivalent to 14 bits has a threshold value of 40
0h to 800h (h represents a hexadecimal number) is used.
That is, since the maximum value in 14-bit encoding is 3FFFh, the threshold value is set to about 1/16 to 1/8 of the maximum allowable amplitude.

The logical product of the click noise detection output signal and the gate signal is taken by the logical product circuit 23, the rising edge of the logical product circuit 23 is held in the holding circuit 24, and the output from the holding circuit 24. The suppression signal suppresses the ADPCM decoded output in the suppression processing circuit 25 inserted on the input side of the PCM decoder 14 by the suppression signal, that is, ADPCM.
The decoded output is zero (removed) or reduced. The holding circuit 24 is reset at the end of the packet at that time. Therefore, the suppression signal continues until the packet at that time ends after the click noise is detected.

If the click noise is detected by the click noise detecting section 22 without providing the holding circuit 24, the vibration attenuation of the click noise is expected, and for example, a pulse width of about several samples of the PCM code. Pulse is output from the click noise detection unit 22, the logical product of this click noise detection pulse and the gate signal is obtained by the circuit 23, and the output pulse of the circuit 23 is used as the suppression signal by the suppression processing circuit 25. May be supplied. This is an embodiment of the invention of claim 3.

In either of the first and second aspects of the invention,
As indicated by the dotted line in FIG. 1, when the substitution processing is performed by the code substitution processing unit 12, a signal indicating that is input to the gate signal generation unit 21, and a gate signal is generated at the end of the packet. Good. Further, although the gate signal is generated in the above description, the gate signal generation unit 21 may be omitted and a pulse may be output from the click noise detection unit 22, and the suppression processing circuit 25 may be directly controlled by this pulse. The holding circuit 24 may be set by the output of the noise detection unit 22, the holding circuit 24 may be reset by the end of the packet at that time, and the suppression processing circuit 25 may be controlled by the output of the holding circuit 24.

Although the present invention has been applied to the reception of ADPCM voice signals in the above description, it can also be applied to the reception of voice signals encoded by other predictive encoders.

[0012]

As described above, according to the present invention, click noise caused by a transmission path error can be suppressed by code replacement, and the internal state does not match with that of the encoder caused by the code replacement. If click-based noise is generated, it is detected and suppressed. In this case, according to the second or third aspect of the invention, the click noise is further suppressed only when the transmission line error is detected by the gate signal of the gate signal generation unit or only when the code replacement is performed. Therefore, the click noise present in the normal signal can be correctly recognized in the normal state.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the invention of claim 1;

FIG. 2 is a block diagram showing a conventional ADPCM receiver.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyoshi Enomoto 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Inventor Shuji Kubota 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corp. (72) Inventor Shuzo Kato 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corp.

Claims (4)

[Claims] 1. A transmission path error of a received predictive encoded speech signal is detected, and when a transmission path error is detected, a predetermined code of the predictive encoded speech signal in that portion is replaced with a specific code. In the predictive coded voice signal receiver supplied to the predictive code decoder, the predictive code is detected by click noise detecting means for detecting click noise from the decoded output of the predict code decoder, and by detecting output of the click noise. A predictive-coded speech signal receiver comprising: a suppression unit that suppresses a decoded signal from a decoder. 2. The predictive coded speech signal is received in packet units, and the suppression by the click noise detection output to the suppression means is gate signal generation means for generating a gate signal by the signal in which the transmission path error is detected. And a means for generating a suppression signal from the click noise detected in the gate signal to the end of the packet at that time, which is performed by the suppression signal. Predictive coded audio signal receiver. 3. Suppression to the suppression means by the click noise detection output includes gate signal generation means for generating a gate signal according to the signal in which the transmission path error is detected, and the click noise detection means includes the click characteristics. A pulse having a predetermined width is generated when noise is detected, and the pulse and the gate signal are logically ANDed by an ANDing means, and the logical product output pulse is used. The predictive coded audio signal receiver described. 4. The predictive coded speech signal receiver according to claim 2 or 3, wherein said gate signal generating means is adapted to generate only when replacement processing for said specific code is performed. .