JP2627579B2 - Audio muting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a CCITT G.100 over an error-prone transmission line such as a digital cordless telephone system. 721 32kbps ADPCM
The present invention relates to an audio muting method when a codec is used.

[0002]

2. Description of the Related Art Conventionally, for example, muting of voice in an analog cordless telephone system has been used in order to prevent a loud sound from being output from a receiver when a reception level is deteriorated or a control signal is transmitted. Also, in a radio using FM, a squelch circuit has been used to prevent noise at the time of reception level deterioration. In the audio muting in these cases, for example, generation of a loud noise is prevented by silencing the audio output to the receiver.

[0003]

However, like the next-generation digital cordless telephone system, CCIT
TG. A muting method using the 721 32 kbps ADPCM codec has not been proposed yet. Further, as in the case of analog, when control is performed to silence the audio signal to the receiver when the reception level is deteriorated, for example, when interference occurs, audio muting cannot be performed and noise occurs.

In view of such a conventional problem, the present invention has been developed, for example, as in the next-generation digital cordless telephone or the like, using the CCITT G.300. An object of the present invention is to propose a muting method applicable to a method using an ADPCM codec such as a 721 32 kbps ADPCM codec.

[0005]

According to the present invention, the above-mentioned object is achieved by the following means. That is, the present invention is realized in the transmission system having a function of performing communication using the ADPCM codec and detecting an error in a transmission frame by the following system. (1) It has a function of detecting that there is an error in consecutive frames or blocks. If the number of consecutive error frames or blocks is equal to or less than a certain value, a signal of an erroneous voice frame or block is immediately transmitted. replaced by frame or block signal transmitted to the codec, in the case of more than a predetermined value, replacing the signal of the audio frame or block has an error in a particular pattern, further, the voice band
Function of narrowing, decoding processing delay time and error of codec
It has a function to compensate for the propagation time,
Block and subsequent frame and block signals
An audio muting method characterized by narrowing the band to prevent noise. (2) Check that consecutive frames and blocks contain errors
Has the ability to be detected, the number of error frames to continue communicating and blocks
If the number of tracks is below a certain value,
The block or block signal was sent to the codec immediately before
Replace with a frame or block signal.
In the above case, the erroneous speech frame or block
Replace the signal with a specific pattern,
Function of narrowing, decoding processing delay time and error of codec
It has a function to compensate for the propagation time,
Block and subsequent frame and block signals
To reduce noise to prevent noise generation.
Audio muting method. (3) A pattern corresponding to a pattern of one word or a plurality of words of the ADPCM codec is prepared in advance, and has a function of performing code conversion between them, and a signal of an erroneous voice frame or block is transmitted to the codec immediately before. It has a function to reduce the received sound volume and a function to compensate for the decoding processing delay time and error propagation time of the codec, and to replace the frame or block with the error and the following An audio muting method characterized in that the reception volume is reduced for a frame or block signal so that excessive volume noise is not heard. (4) It has a function of detecting an error in consecutive frames and blocks and a function of preparing a pattern corresponding to a pattern of one or more words of the ADPCM codec and performing code conversion between them. If the number of consecutive error frames or blocks is equal to or less than a certain value, the signal of an erroneous voice frame or block is
Replace with the signal of the frame or block transmitted to the codec immediately before, and if errors continue beyond a certain value, code the signal of the erroneous voice frame or block to the signal of the frame or block transmitted to the codec immediately before. An audio muting method characterized by replacing the converted signal to prevent generation of noise. (5) A pattern corresponding to a pattern of one or more words of the ADPCM codec is prepared in advance, and has a function of performing code conversion between these patterns. Do
An audio muting method characterized by preventing generation of noise. With the above method, a high-quality call can be made without generating a loud noise at the time of level deterioration or occurrence of interference.

[0006]

FIG. 1 is a diagram showing an example of a block configuration according to the present invention for performing audio muting. In FIG. 1, 11 is an antenna, 12 is a receiver, 13 is a demodulator for demodulating a digital signal, 14 is an error detection device for detecting an error in a demodulated transmission frame, and 15 is an error detection device. Muting circuit (I) that performs muting in the ADPCM signal portion according to the command
Reference numeral 16 denotes an ADPCM decoder for converting an ADPCM signal into an analog audio signal, reference numeral 17 denotes a muting circuit (II) for performing muting in an analog audio signal portion in accordance with a command from the error detection device 14, and reference numeral 18 denotes a receiver.

As means for realizing the error detection device 14, for example, a method of adding an error detection code in a transmission frame to perform signal transmission and detect an error, and a method of detecting an error of a voice signal from an error of a frame synchronization pattern. An estimation method or the like can be used. The error detection device 14 will be described below with reference to FIG.
Will be described.

FIG. 2 is a diagram showing an example of a transmission frame configuration in a wireless section. In FIG. 2, 21 is a preamble,
Reference numeral 22 denotes a frame synchronization pattern for synchronizing frames, reference numeral 23 denotes an audio signal, and reference numeral 24 denotes an error detection code added on the transmission side so that errors in the audio signal can be detected. Hereinafter, the entire audio signal 23 in one transmission frame is referred to as an audio frame.

As a method using an error detection code, for example, CRC or BCH can be used. For codes such as BCH, the error rate can be measured because the number of error bits can be measured. However, such a code is complicated in encoding and decoding, and the number of detectable errors is limited. With codes such as CRC, detection is easy and the non-detection rate can be suppressed to a negligible level, but the number of errors is not known.

By using a more advanced error detection code, it is possible to know where in the audio signal 23 an error has occurred. For example, if the audio signal 23 is divided into a plurality of blocks and error detection is performed by CRC for each block, it is possible to know in which block an error has occurred.
An example is shown in FIG.

In FIG. 2, an audio signal 23 is divided into three blocks, and error detection is performed by CRC for each block. That is, in this example, one audio frame is composed of three blocks. When constructing a transmission frame, the CRC of each block is put together, for example, as an error detection code 24 and placed after the transmission frame. As a method of estimating an error of the audio signal 23 from the frame synchronization pattern 22,
For example, in the case of performing frame synchronization, a method of permitting some bits of error and performing frame synchronization, and estimating the error on the audio signal 23 on the assumption that errors occur at the same rate as the frame synchronization pattern Etc.

A drawback of the error detection method based on this estimation is that when the error detection code 24 is used, errors in the audio signal 23 can be found directly, whereas errors are indirectly estimated. The inability to find the error accurately. On the other hand, the merit is that the frame efficiency is high because the code for detection is not required.

The error detection device 14 instructs, for example, the muting circuit (I) 15 and the muting circuit (II) 17 for detecting an error by the above-described method, to muting the audio frame or block.

If the error rate can be detected, for example, muting is performed only when the error rate exceeds a threshold, or the muting method is changed depending on the level of the error rate. It is also possible to minimize the distortion of the sound generated due to muting.
Further, the error rate that can be estimated from the frame synchronization pattern 22 is usually based on the fact that the error rate has become considerably high, and the error detection code 24 uses a simple code that detects only the presence or absence of an error. There is also a method of changing the muting method depending on the level of the muting.

An embodiment of the muting system according to the present invention will be described below. FIG. 3 is a diagram showing the principle when the muting circuit (I) 15 is used in the audio muting system according to the first aspect. FIG. 3 shows an example in which two words of the original audio signal have an error. Here, for example, an ADPCM codec in which one word is 4 bits is assumed. If the error portion can be detected by the error detection device 14, the muting circuit (I) 15 replaces the error portion with a specific pattern such as “0001”, Send a signal. If the error detection device 14 cannot detect the error part, all the signals in the frame are replaced with the above pattern.

The specific pattern need not be one word, but may be a pattern extending over a plurality of words, such as "00011110". The muting control can be performed more finely with a pattern having a longer word number. In the above replacement, what pattern is most suitable depends on the characteristics of the ADPCM codec. In the following, CCITT G. 721 32kbps
4 shows a pattern when the ADPCM codec is used.

FIG. 4 shows CCITT G. 721 32 kb
FIG. 4 shows a part of a block diagram of a decoder input part of a psADPCM codec. In FIG. 4, reference numeral 41 denotes an adaptive inverse quantizer that generates a quantized difference signal DQ from an input code, and reference numeral 42 denotes a quantizer scale factor adaptation unit that generates an exponent part of the quantized difference signal DQ. I is the input signal 1 to ADPCM
Word, DQLN is a log ₂ normalized quantized difference signal, DQL is a log ₂ quantized difference signal, DQS is a sign bit of the quantized difference signal, Y is a quantized scale factor,
DQ is a quantization difference signal, WI is a quantization multiplier, and YUT is a high-speed quantization scale factor. RECONST43
Is a log ₂ normalized quantized difference signal D of the input signal I.
Table 1 shows a conversion table for the blocks that convert to QLN. The adder 44 is a block that generates a log ₂ quantized difference signal DQL by adding a quantized scale factor Y corresponding to an exponent to the log ₂ normalized quantized difference signal DQLN corresponding to a mantissa. The antilogarithmic unit 45 is a block that generates a quantized difference signal from the log ₂ quantized difference signal DQL and the sign bit DQS of the quantized difference signal. The FUNCTW 46 converts the input signal I into a quantization multiplier WI
Table 2 shows the conversion table for the blocks converted to. FI
LTD 47 is a block for generating a high-speed quantization scale factor YUT which is a basis for determining the next quantization scale factor from the quantization multiplier WI and the quantization scale factor Y.

Input stage RECONST 43 and FUNC
As can be seen from Tables 1 and 2 which are conversion tables of TW46, "0000" and "1111" are input words.
Is input, the scale factor and the transform code of the adaptive inverse quantizer become very large. Conversely, the change amount is small for the input of “0001” or “1110”. Therefore, when an error occurs in the transmission path of the audio signal, “000”
If interpolation is performed with a code having a small change amount such as “1”, it can be said that the possibility of generating large noise is small.

[0019]

[Table 1]

[0020]

[Table 2]

Next, an example according to claim 1 will be described below. Figure
FIG. 5 is a diagram showing an example of a case where the muting circuit (I) 15 is used in the audio muting method according to claim 1 . FIG. 5 shows an example in which, when the number of consecutive error frames is three or more, audio muting for replacing with a specific pattern such as “0001” is performed.
An example in which an erroneous frame is received twice consecutively is shown.

Since the first frame (No. 1 in the figure) has no error, the original audio signal and the signal after muting are the same. In the second frame (No. 2), there is an error in the frame.
It is sent to the CM decoder 16. Third frame (No. 3)
Is also incorrect, but since the number of consecutive errors is 2, the third
Instead of transmitting a frame, the frame (No. 1) transmitted immediately before is transmitted to the ADPCM decoder 16. 4th
There is also an error in the frame. In this case, the number of consecutive errors is 3
Therefore, the signal in the fourth frame is rewritten to the pattern of “0001” and the signal is transmitted to the ADPCM decoder 16. Similarly, when the error continues four or more times, the signal in the frame is similarly rewritten to the pattern of "0001" and
The signal is sent to the DPCM decoder 16.

When a frame having the number of consecutive errors of less than 3 and having no error is received, the number of consecutive errors is returned to 0, and the first
Start with sending a frame.

The purpose of this audio muting method is to remove the unnaturalness that occurs when the same frame is transmitted continuously. As described above, in the case where an error occurs continuously for a time longer than the time that can be regarded as a continuation of the same waveform, unnaturalness becomes noticeable in the audio muting method according to the second aspect. The muting method is a method for preventing this. Therefore, the permissible value of the number of continuous errors is closely related to the frame length, and needs to be equal to or less than a time at which the same waveform can be regarded as continuous.

Next, an example according to claim 3 will be described below. Figure
6 is a diagram showing an example of a case where the audio muting method according to claim 3 is used as the muting circuit (I) 15, for example. 6 (a) shows an example of a case portion of the error in the speech frame is not known, muting circuit 1
5 receives the indication of an erroneous frame from the error detection device 14 and converts the speech frame into an ADPCM decoder 16.
Instead of sending the audio frame, the voice frame sent immediately before is subjected to code conversion and then sent. 6 (b) is an example of a case portion of the error in the speech frame is a clear, muting circuit 15 receives the indication of the block (No.3) with errors in the frame from the error detector 14, Instead of the block, code conversion is performed on the immediately preceding block (No. 2), and the converted block (No. 2 ') is copied and sent to the ADPCM decoder 16. Table 3 shows an example of the code conversion.

[0026]

[Table 3]

The purpose of the audio muting method is as follows.
Simply using the signal sent immediately before in place of the site where the error occurred leaves unnaturalness, so the following code is subjected to the following conversion processing and then sent out as the frame.
It is to eliminate unnaturalness. As a code conversion method, for example, as shown in Table 3 above, the code conversion of the original audio signal is performed so that the input to the ADPCM codec is reduced. This conversion method is not limited to the method shown in Table 3, but is also used in Tables 1 and 2
As can be seen from the characteristics of the ADPCM codec of
Any method may be used as long as the original speech code is transcoded so that the input to the CM codec is reduced.

In addition to the conversion for each word as shown in Table 3, a code conversion method using a pattern corresponding to a plurality of words may be used. Table 4 shows an example of this case. The example of Table 4 shows an example of a pattern for converting an ADPCM codec signal for two words. In code conversion of a plurality of words, more detailed conversion can be performed than in code conversion for each word and unnaturalness is reduced, but there is a disadvantage that a code conversion pattern increases.

[0029]

[Table 4]

Next, an example according to claim 5 will be described below. Figure
FIG. 7 is a diagram showing an example of the case where the audio muting method according to claim 4 is used as the muting circuit (I) 15, for example. FIG. 7 shows that, for example, if the number of consecutive error frames is three or less,
In the example where audio is muted such that the frame is transmitted to the DPCM codec and the code is converted to the immediately preceding frame when the frame is transmitted three or more times, the frame is transmitted continuously.
An example is shown where a wrong frame is received.

In FIG. 7 , the first frame (No.
In 1), since there is no error, the original audio signal and the signal after muting are the same. In the second frame (No. 1), since there is an error in the frame, the first frame transmitted immediately before is transmitted to the ADPCM decoder 16 instead. Although the third frame (No. 1) also has an error, since the number of consecutive errors is 2, the immediately preceding frame (No. 1) is transmitted to the ADPCM decoder 16 instead of transmitting the third frame. . There is also an error in the fourth frame. In this case, since the number of consecutive errors is 3, the signal of the frame transmitted immediately before is subjected to, for example, code conversion in Table 3, and the signal (No. 1 ') is transmitted to the ADPCM decoder 16. There is also an error in the fifth frame. Also in this case, since the consecutive errors are three or more times, the signal of the frame transmitted immediately before is subjected to, for example, code conversion shown in Table 3 and the signal (No. 1 ") is transmitted to the ADPCM decoder 16. Similarly, when the error is repeated more than once, the signal is transmitted to the ADPCM decoder 16 after the code conversion of the frame transmitted immediately before is performed. The number of errors is returned to 0, and transmission from the first frame is started.

In the above example, the code conversion pattern shown in Table 3 is used even when the error is repeated four or more times. However, a method of switching the code conversion pattern according to the number of consecutive errors may be used. Further, in the above example, the conversion for each word in Table 3 was performed as the code conversion pattern, but a multi-word code conversion pattern as shown in Table 4 may be used, for example.

Next, an example according to claim 5 will be described below. Figure
FIG. 8 is a diagram showing an example in the case where the audio muting method according to claim 6 is used as the muting circuit (I) 15, for example. 8 (a) is an example of a case portion of the error in the speech frame is not known, muting circuit 15
Receives the indication of an erroneous frame from the error detection device 14, performs code conversion on the entire speech frame,
The data is sent to the M decoder 16. FIG. 8B shows an example in which an error part in a voice frame is clear. When the muting circuit 15 receives an indication of an erroneous block (No. 2) in the frame from the error detection device 14, The block is subjected to code conversion, and the converted block (No. 2 ′) is sent to the ADPCM decoder 16. Table 5 shows an example of the code conversion.

[0034]

[Table 5]

The purpose of the audio muting method is as follows.
When a code error occurs, it is rare that all the data at the portion where the error is detected is erroneous, and the utterance is output using data that is not erroneous without impairing the naturalness. As a code conversion pattern for this purpose, for example, as shown in Table 5 above, it is desirable to perform code conversion on the audio signal so that the output of the ADPCM decoder does not suddenly change. That is, the conversion differs depending on the size of the input to the ADPCM codec. In the case of a small input having little influence on the output, the input is kept as it is, and in the case of a large input causing a rapid change in the output, the conversion is made to a smaller value. This conversion method is not limited to the method shown in Table 3, and as can be seen from the characteristics of the ADPCM codec shown in Tables 1 and 2,
If the input to the M codec is small, leave it as is,
In the case of a large input, a code conversion pattern for converting to a smaller value may be used.

In addition to the conversion for each word as shown in Table 5, a code conversion method using a pattern corresponding to a plurality of words may be used. Table 6 shows an example of this case. The example of Table 6 shows an example of a pattern for converting an ADPCM codec signal for two words. In code conversion of a plurality of words, more detailed conversion can be performed than in code conversion for each word and unnaturalness is reduced, but there is a disadvantage that a code conversion pattern increases. In this case, if the input to the ADPCM codec is small, the code conversion pattern may be left as it is, and if the input is large, a code conversion pattern for converting to a smaller value may be used.

[0037]

[Table 6]

Next, the muting method according to claim 1
An example of the muting circuit (II) used for the following is shown below.
FIG. 9 is a diagram showing an example of a device configuration of the muting circuit (II) 17 in this case . In FIG. 9 , 101
Is a band variable filter that functions to narrow the voice band when a transmission error occurs, and 102 is a processing delay time and error propagation time compensation circuit inside the ADPCM codec.

One of the functions of the ADPC is to take into account the processing delay time inside the ADPCM codec,
The variable bandpass filter 10 is not at the timing of inputting the signal to the M codec but at the timing at which the signal is output.
1 has a function as a compensation circuit for operating the circuit. The second function is to function as a compensation circuit for the error propagation time described below. The ADPCM codec has an adaptive prediction unit inside. When erroneous data is input, a discrepancy occurs between the adaptive prediction unit of the ADPCM codec on the encoding side and the adaptive prediction unit on the decoding side, and noise is generated. Occur. Therefore, there is a possibility that noise is generated due to error propagation for a certain time after input of erroneous data, and it is necessary to operate the variable bandpass filter 101.

In the above example, the delay time and error propagation time compensation circuit 102 operates the variable bandpass filter 101 according to the characteristics of the ADPCM codec, but the variable bandpass filter 101 is simply applied to the next frame or all blocks. 101 may be operated.

FIG. 10 shows an example in which the location of an error in a voice frame is unknown. When the muting circuit 17 receives an indication of an erroneous frame from the error detection device 14,
The variable bandpass filter 101 is operated in consideration of the processing delay time and the error propagation time inside the ADPCM codec. If the location of the error in the audio frame is clear,
At 10 , the frame may be read as a block.

In the above example, the muting circuit (II) 17
Has been described taking muting of an analog part as an example, but muting can be similarly performed in the PCM part by performing μ1aw⇔linear conversion and using a digital filter.

Next, a muting method according to claim 2
An example of the muting circuit (II) used for the following is shown below.
FIG. 11 is a diagram showing an example of a device configuration of the muting circuit (II) 17 in this case . In FIG. 11 , 12
Reference numeral 1 denotes a level suppression circuit that attenuates the level of a sound when a transmission error occurs, and 122 denotes a delay time and error propagation time compensation circuit. 122 functions, ADPC 9
This is the same as the processing delay time and error propagation time compensation circuit 102 of the M codec. Further, the delay time and error propagation time compensation circuit 122 may simply operate the level suppression circuit 121 for the next frame or all blocks, similarly to the delay time and error propagation time compensation circuit 102 in FIG.

FIG. 12 shows an example in which an error part in an audio frame is unknown. When the muting circuit (II) 17 receives an indication of an error frame from the error detection device 14, the muting circuit (II) 17 The level suppress circuit 121 is operated in consideration of the processing delay time and the error propagation time. If the site of the error in the speech frame clear may In other read as block frame in FIG.

In the above example, the muting circuit (II) 17
Has been described taking muting in an analog part as an example, but muting is also possible in the PCM part by performing μ1aw⇔linear conversion and performing digital level conversion.

In FIG. 1, muting circuit (I)
15 and the muting circuit (II) 17 work in a mutually interpolating manner. In the muting method using only the muting circuit (I) 15 , code conversion is performed on the input side of the ADPCM codec, so that noise may be generated in some cases. Muting circuit (II) 17
The muting scheme using only also be suppressed becomes slightly unnatural voice itself is performed a sufficient noise suppression. As exemplified in FIG. 1, for example, a muting circuit (I) 1
Muting method and muting circuit using 5
By combining the muting methods using (II) 17, it is possible to configure better muting.

[0047]

As described above, according to the present invention,
In a transmission system that performs communication using the ADPCM codec, the use of the audio muting described in the claims alone or in combination prevents simple generation of noise even when a transmission error occurs. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an audio muting system according to the present invention.

FIG. 2 is a configuration diagram of a transmission frame in a transmission system targeted by the present invention.

FIG. 3 is a signal pattern illustrating an operation example of a muting circuit (I) used in the present invention.

FIG. 4 is a block diagram showing an example of a decoder input portion of an ADPCM codec used in the present invention.

FIG. 5 is a signal pattern showing another operation example of the muting circuit (I) used in the present invention.

FIG. 6 is a signal pattern showing another operation example of the muting circuit (I) used in the present invention.

FIG. 7 is a signal pattern showing another operation example of the muting circuit (I) used in the present invention.

FIG. 8 is a signal pattern showing another operation example of the muting circuit (I) used in the present invention.

FIG. 9 is a block diagram illustrating a configuration example of a muting circuit (II) used in the present invention.

FIG. 10 is a time chart for explaining the operation of the configuration example of FIG. 9;

FIG. 11 is a block diagram illustrating a configuration example of a muting circuit (II) used in the present invention.

FIG. 12 is a time chart for explaining the operation of the configuration example of FIG. 11;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Antenna 12 Receiver 13 Demodulator 14 Error detection device 15 Muting circuit (I) 16 ADPCM decoder 17 Muting circuit (II) 18 Handset 21 Preamble 22 Frame synchronization pattern 23 Audio signal 24 Error detection code 41 Adaptive inverse quantizer 42 Quantization scale factor adaptation unit RECONST 43 Block for converting input signal 1 to log ₂ normalized quantization difference signal DQLN 44 Adder 45 Antilogarithmizer FUNCTW46 Block for converting input signal I to quantization multiplier WI FILTD47 High speed Block 101 for generating quantization scale factor YUT 101 Band variable filter 102 Delay time and error propagation time compensation circuit 121 Level suppress circuit 122 Delay time and error propagation time compensation circuit

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-268317 (JP, A) JP-A-58-147810 (JP, A) JP-A-63-16472 (JP, A) 48994 (JP, B2)

Claims (5)

(57) [Claims] In a transmission system having a function of performing communication using an ADPCM codec and detecting an error in a transmission frame, consecutive frames and blocks have an error.
Has the function of detecting
If the number of blocks is less than a certain value, an erroneous sound
Sends the voice frame or block signal to the codec immediately before
Replaced with the received frame or block signal, fixed value
In the above case, the error frame or block
Replace the signal with a specific pattern,
Function of narrowing, decoding processing delay time and error of codec
It has a function to compensate for the propagation time,
Block and subsequent frame and block signals
An audio muting method characterized by narrowing the band to prevent noise. 2. Communication is performed using an ADPCM codec.
Transmission method with a function to detect errors in transmission frames
Error in consecutive frames or blocks in formula
Has the function of detecting
If the number of blocks is less than a certain value, an erroneous sound
Sends the voice frame or block signal to the codec immediately before
Replaced with the received frame or block signal, fixed value
In the above case, the error frame or block
Replace the signal with a specific pattern,
Squeezing function, codec decoding delay time and error propagation
It has a function to compensate the seeding time,
For lock and subsequent frame and block signals
To reduce the listening volume so that excessive volume noise is not heard.
Features and to Ruoto voice muting method to. 3. Communication is performed using an ADPCM codec.
Transmission method with a function to detect errors in transmission frames
In the formula, a pattern corresponding to a pattern of one word or a plurality of words of the ADPCM codec is prepared in advance, and has a function of performing code conversion between these, and transmits a signal of an erroneous voice frame or block to the codec immediately before. by replacing the signal of the frame or block to the code converted signal, wherein the to Ruoto <br/> voice muting method to prevent the occurrence of noise. 4. Communication is performed using an ADPCM codec.
Transmission method with a function to detect errors in transmission frames
In the formula, there is a function of detecting an error in a continuous frame or block, and a function of preparing a pattern corresponding to a pattern of one or more words of the ADPCM codec in advance and performing code conversion between them. If the number of consecutive error frames or blocks is equal to or less than a certain value, the signal of the erroneous voice frame or block is replaced with the signal of the frame or block transmitted to the codec immediately before. If consecutive, the signal of the erroneous voice frame or block is
Replacing a frame or block signal that sent to the codec just prior to the code converted signal, wherein the to Ruoto voice muting method to prevent the occurrence of noise. 5. Communication is performed using an ADPCM codec.
Transmission method with a function to detect errors in transmission frames
In the formula, a pattern corresponding to a pattern of one word or a plurality of words of the ADPCM codec is prepared in advance, and has a function of performing code conversion between them, and performs the code conversion on a signal of an erroneous voice frame or block. performed, characteristics and be Ruoto voice muting method to prevent the occurrence of noise.