JP2000353968A - Audio decoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of a big noise by interrupting output of an audio signal by a switch which permits or inhibits output of a decoder when there exists an error that cannot be corrected by a error corrector for correcting an error of a detected signal. SOLUTION: A bit stream signal detected by a demodulator 101 is inputted to an error corrector 102 and error correction is performed by using error correction information superimposed in the bit stream. The bit stream signal which is error corrected is inputted to a decoder 103 and is decoded to an audio signal before encoding. When a frequency of error is high and all the errors cannot be corrected by the error corrector 102, the information is transmitted from the error corrector 102 to a switch 104 and the switch 104 inhibits output of the audio signal of an output of the decoder 103. The switch 104 is the one that permits or inhibits the output of the decoder 103.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio decoding device for transmitting an encoded audio signal and a digital wireless microphone system using the same.

[0002]

2. Description of the Related Art Conventionally, as this type of apparatus, there has been an audio decoding apparatus as shown in FIG. In FIG. 8, a demodulator 801 detects a received signal.
The error corrector 802 corrects an error existing in the detected baseband signal. Decoder 803
Converts an error-corrected bit stream signal into an audio signal. As described above, also in the above-described conventional example, it is possible to decode a signal transmitted and compressed.

[0003]

However, in the above-described conventional audio decoding apparatus, the error correction unit 802
When an error exceeding the error correction capability occurs, the bit stream signal containing the error is decoded. At this time, there is a problem that an extremely large noise is generated in the audio signal output from the decoder 803. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned conventional problem, and to provide an excellent audio decoding device which does not generate large noise even when an error exceeding the correction capability of an error corrector occurs.

[0004]

An audio decoding apparatus according to the present invention comprises a demodulator for detecting a received signal, an error corrector for correcting an error in the detected signal, and an audio signal for correcting the error-corrected signal. And a switch for permitting or prohibiting the output of the decoder, and when an error that cannot be corrected by the error corrector exists, the output of the audio signal is stopped by the switch. It has a configuration as follows. With this configuration, when an error that exceeds the correction capability of the error corrector occurs, the output of the audio signal is stopped, so that no large noise is generated.

[0005] Further, an audio decoding device according to the present invention includes a level control device in addition to the above configuration.
By gradually increasing the output level with a constant time constant when returning from the error processing, a natural error recovery can be achieved in terms of audibility.

An audio decoding apparatus according to the present invention includes a demodulator for detecting a received signal, an error corrector for correcting an error in the detected signal, and a decoding for converting the error-corrected signal into an audio signal. Device, and a switch for selectively permitting or stopping the audio signal for each sub-band, and when there is an error that cannot be corrected by the error corrector, an audio signal other than the lowest frequency sub-band by the switch. Is stopped. With this configuration, a signal in a band where energy such as human voice is unevenly distributed is reproduced, and among errors, only errors in a high frequency band that is easily detected audibly can be suppressed.

In addition, the audio decoding apparatus of the present invention has a level control device in addition to the above-described configuration. When returning from error processing, the output level is gradually increased with a constant time constant, so Natural error recovery can be performed.

The audio decoding apparatus according to the present invention comprises a demodulator for detecting a received signal, an error corrector for correcting an error in the detected signal, and a decoding for converting the error-corrected signal into an audio signal. A dequantizer that dequantizes the error-corrected signal and converts the error-corrected signal into an audio signal for each subband; a synthesis filter device for synthesizing the audio signal for each subband; A sine wave generator that replaces the low-frequency band sub-band signal with a single frequency sine wave, corrects the phase, and outputs
A switch for selectively permitting or stopping the audio signal for each of the subbands, wherein when an error that cannot be corrected by the error corrector exists, the synthesis filter is used for the signal of the subband of the lowest frequency by the switch. The output from the device or the sine wave generator is selected, and the output of audio signals of other subbands is stopped. With this configuration, if there is an error that cannot be corrected by the error corrector, the signal of the lowest frequency subband is replaced with a single frequency sine wave, the phase is corrected and output, and the audio signal of the other subband is output. By stopping the output, it is possible to remove an error while maintaining the sound quality of a signal having a strong spectrum such as a human voice and having a small temporal variation.

The audio decoding apparatus according to the present invention further includes a level control device in addition to the above-described configuration. When returning from the error processing, the output level is gradually increased with a constant time constant, thereby improving the audibility. Natural error recovery can be performed.

The audio decoding apparatus according to the present invention further includes a level control device in addition to the above-described configuration. By gradually attenuating the level of the sine wave, a sense of incongruity that occurs when a long-term error continues is provided. Can be suppressed.

Further, a digital wireless microphone system according to the present invention comprises the above-mentioned audio decoding device, and each of the above-mentioned audio decoding devices can be applied to a digital wireless microphone system.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS. (Embodiment 1) FIG. 1 shows the configuration of an audio decoding apparatus according to Embodiment 1 of the present invention. In FIG. 1, a demodulator 101 detects a received signal. The error corrector 102 corrects an error existing in the detected baseband signal. The decoder 103 converts the error-corrected bit stream signal into an audio signal. The switch 104 allows or prohibits the output of the decoder 103.

The operation of the audio decoding device configured as described above will be described. First, the demodulator 101
The bit stream signal detected by this is input to the error corrector 102, and performs error correction using the error correction information superimposed in the bit stream. The error-corrected bit stream signal is input to the decoder 103,
It is decoded into an audio signal before encoding. On the other hand, if the error frequency is high and all errors cannot be corrected by the error corrector 102,
Is transmitted to the switch 104, and the switch 104
The output of the audio signal which is the output of No. 3 is prohibited.

As described above, according to the first embodiment of the present invention, even when an error exceeding the correction capability of the error corrector occurs, it is possible to suppress the generation of large noise due to the error.

(Embodiment 2) FIG. 2 shows a configuration of an audio decoding apparatus according to Embodiment 2 of the present invention. In FIG. 2, a demodulator 201 detects a received signal. The error corrector 202 corrects an error existing in the detected baseband signal. The decoder 203 converts the error-corrected bit stream signal into an audio signal. The switch 204 permits or prohibits the output of the decoder 203. The level control device 205 controls the level of the output signal of the decoder 203.

Next, the operation will be described. As in the first embodiment, when an error that exceeds the correction capability of the error corrector 202 occurs, the switch 204 inhibits the output of the audio signal. Thereafter, when the error exceeding the error correction capability no longer occurs, the output is not restarted immediately, but the output level is gradually increased by the level control device 205, and after a certain period of time, the original output level is increased. Level.

As described above, according to the second embodiment of the present invention, when the occurrence of an error exceeding the correction capability of the error corrector is completed, the error can be recovered naturally from the viewpoint of hearing.

(Embodiment 3) FIG. 3 shows a configuration of an audio decoding apparatus according to Embodiment 3 of the present invention. In FIG. 3, a demodulator 301 detects a received signal. The error corrector 302 corrects an error present in the detected baseband signal. The inverse quantization device 303 inversely quantizes the bit stream signal to generate an audio signal for each subband. The synthesis filter 304 is a pre-filter for synthesizing an audio signal for each subband. The switch 305 permits or prohibits the output of an audio signal other than the sub-band of the lowest frequency band. The adder 306 synthesizes the audio signal of each subband permitted by the switch 305.

Next, the operation will be described. As in the first embodiment, when an error exceeding the correction capability of the error corrector 302 occurs, only the audio signal of the lowest frequency sub-band is output by the switch 305, and the output of the audio signal of the other bands is stopped. I do.

As described above, according to the third embodiment of the present invention, a signal in a band where energy such as human voice is unevenly distributed is reproduced, and only errors in a high frequency band which are easily detected audibly among errors are reproduced. Can be suppressed.

(Embodiment 4) FIG. 4 shows the configuration of an audio decoding apparatus according to Embodiment 4 of the present invention. In FIG. 4, a demodulator 401 detects a received signal. The error corrector 402 corrects an error existing in the detected baseband signal. The inverse quantization device 403 inversely quantizes the bit stream signal to generate an audio signal for each subband. The synthesis filter 404 is a pre-filter for synthesizing an audio signal for each subband. The switch 405 permits or prohibits the output of audio signals other than the sub-band of the lowest frequency band. The level control device 406 controls the level of the output signal from the switch 405. Adder 4
Reference numeral 07 is for synthesizing the audio signal of each sub-band, which is permitted by the switch 405 and whose level is controlled by the level control device 406.

Next, the operation will be described. As in the third embodiment, when an error exceeding the correction capability of the error corrector 402 occurs, the switch 405 prohibits the output of audio signals other than the subband of the lowest frequency band.
Thereafter, when an error exceeding the correction capability of the error correction does not occur, the output is not restarted immediately, but the output level is gradually increased by the level control device 406, and after a lapse of a certain time, the original output level is increased. Level.

As described above, according to the fourth embodiment of the present invention, when the occurrence of an error exceeding the correction capability of the error corrector is completed, it is possible to recover the error naturally from the viewpoint of hearing.

(Embodiment 5) FIG. 5 shows the configuration of an audio decoding apparatus according to Embodiment 5 of the present invention. In FIG. 5, a demodulator 501 detects a received signal. The error corrector 502 corrects an error existing in the detected baseband signal. The inverse quantization device 503 inversely quantizes the bit stream signal to generate an audio signal for each subband. The synthesis filter 504 is a pre-filter for synthesizing an audio signal for each subband. The sine wave generator 505 replaces the signal of the lowest frequency subband with a sine wave of a single frequency, corrects the phase, and outputs the corrected signal. The switch 506 permits or prohibits the output of audio signals other than the subband of the lowest frequency band, and outputs the output of the synthesis filter device 504 and the sine wave generator 5 for the subband of the lowest frequency band.
05 is permitted and the other output is prohibited.

FIG. 6 shows a part of the sine wave generator 505 and the switch 506 in FIG. 5 in detail.
In FIG. 6, a frequency counter 601 measures the frequency of an input subband signal having the lowest frequency. The buffer 602 holds a signal one frame before. The sine wave oscillator 603 generates a sine wave of the frequency measured by the frequency counter 601. The phase comparator 604 controls the phase of the sine wave generated by the sine wave oscillator 603, and maintains continuity of the phase of the signal one frame before remaining in the buffer 602. The switch 605 permits one of the output of the inverse quantization device 503 in FIG. 5 and the output of the phase comparator 604 in FIG. 6, and prohibits the other output.

[0026]
Next, the operation will be described with reference to FIG. The input signal of the lowest frequency sub-band is
It is input to the frequency counter 601 and measures the predominant frequency in the subband. The sine wave oscillator 603 generates a sine wave having a frequency equal to the frequency measured by the frequency counter 601. On the other hand, the signal of the sub-band is input to the buffer 602 and held for one frame. The sine wave generated by the sine wave oscillator 603 is input to the phase comparator 604, and is subjected to phase control so as to maintain continuity of the phase of the signal one frame before held in the buffer 602. The output of the phase comparator 604 and the output of the inverse quantizer 503 in FIG. 5 are input to the switch 605. Selects the output of the phase comparator 604.

As described above, according to the fifth embodiment of the present invention, when an error occurs, sound quality is maintained for a signal having a strong spectrum and a small temporal variation, such as a human voice. It is possible to eliminate errors while doing so.

Embodiment 6 FIG. 7 shows a configuration of an audio decoding apparatus according to Embodiment 6 of the present invention. In FIG. 7, a demodulator 701 detects a received signal. The error corrector 702 corrects an error existing in the detected baseband signal. The inverse quantization device 703 inversely quantizes the bit stream signal to generate an audio signal for each subband. The synthesis filter 704 is a pre-filter for synthesizing an audio signal for each subband. The sine wave generator 705 replaces the signal of the lowest frequency subband with a sine wave of a single frequency, corrects the phase, and outputs the corrected signal. The switch 706 permits or prohibits the output of an audio signal other than the sub-band of the lowest frequency band. The output is permitted and the other output is prohibited. The level control device 707 is
The level of the output signal after the switch 706 is controlled. The adder 708 synthesizes an audio signal for each subband, which is enabled by the switch 706 and whose level is controlled by the level control device 707.

Next, the operation will be described. As in the fifth embodiment, when an error exceeding the correction capability of the error corrector 702 occurs, the switch 706 prohibits the output of audio signals other than the lowest frequency band sub-band.
Thereafter, when an error exceeding the correction capability of the error correction does not occur, the output is not restarted immediately, but the output level is gradually increased by the level control device 707, and after a lapse of a certain time, the original output level is increased. Level.

As described above, according to the sixth embodiment of the present invention, when the occurrence of an error exceeding the correction capability of the error corrector is completed, a natural error recovery can be perceived.

(Embodiment 7) An audio decoding apparatus according to Embodiment 7 of the present invention has a configuration similar to that of Embodiment 6, and therefore the operation thereof will be described with reference to FIG. As in the fifth embodiment, when an error exceeding the correction capability of the error corrector 702 occurs, the switch 706 prohibits the output of audio signals other than the lowest frequency band sub-band. In addition, the output of the audio signal other than the subband of the lowest frequency band is also controlled by the level control device 7.
07, the output level is attenuated little by little, and the output is stopped after a certain period of time.

As described above, according to the seventh embodiment of the present invention, by gradually attenuating the level of the sine wave,
It is possible to suppress a sense of incongruity that occurs when long section errors continue.

[0033]

As described above, according to the audio decoding apparatus of the present invention, when an error that cannot be corrected by the error corrector is present, the output of the audio signal is stopped by the switch, so that a large noise caused by the error is eliminated. The effect that generation can be suppressed can be obtained.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of an audio decoding device according to a first embodiment of the present invention.

FIG. 2 is a functional block diagram of an audio decoding device according to a second embodiment of the present invention.

FIG. 3 is a functional block diagram of an audio decoding device according to a third embodiment of the present invention.

FIG. 4 is a functional block diagram of an audio decoding device according to a fourth embodiment of the present invention.

FIG. 5 is a functional block diagram of an audio decoding device according to a fifth embodiment of the present invention.

FIG. 6 is a detailed block diagram for explaining an operation of the audio decoding device according to the fifth embodiment of the present invention.

FIG. 7 is a functional block diagram of an audio decoding device according to Embodiment 6 of the present invention and Embodiment 7 of the present invention;

FIG. 8 is a functional block diagram of a conventional audio decoding device.

[Explanation of symbols]

101, 201, 301, 401, 501, 701, 8
01 demodulator 102, 202, 302, 402, 502, 702, 8
02 error corrector 103, 203, 803 decoder 104, 204, 305, 405, 506, 605, 7
06 Switch 205, 406, 707 Level control device 304, 404, 504, 704 Synthesis filter device 306, 407, 507, 708 Adder

Claims (8)

[Claims] 1. A demodulator for detecting a received signal, an error corrector for correcting an error of the detected signal, a decoder for converting the error-corrected signal into an audio signal,
An audio decoding device comprising: a switch for permitting or prohibiting the output of the decoder, and when there is an error that cannot be corrected by the error corrector, the switch stops the output of the audio signal. 2. The audio decoding device according to claim 1, further comprising a level control device, wherein the output level is gradually increased with a constant time constant when returning from error processing. 3. A demodulator for detecting a received signal, an error corrector for correcting an error in the detected signal, a decoder for converting the error-corrected signal into an audio signal,
A switch for selectively permitting or stopping the audio signal for each sub-band, and when there is an error that cannot be corrected by the error corrector, the switch outputs an audio signal other than the lowest frequency sub-band. An audio decoding device that stops. 4. The audio decoding device according to claim 3, further comprising a level control device, wherein the output level is gradually increased with a constant time constant when returning from the error processing. 5. A demodulator for detecting a received signal, an error corrector for correcting an error of the detected signal, a decoder for converting the error-corrected signal to an audio signal,
An inverse quantization device that inversely quantizes the error-corrected signal and converts it into an audio signal for each sub-band; a synthesis filter device for synthesizing the audio signal for each sub-band; A sine wave generator that replaces a sub-band signal with a single-frequency sine wave and corrects and outputs a phase; and a switch that selectively enables or stops an audio signal for each of the sub-bands, wherein the error corrector When there is an error that cannot be corrected by the switch, the switch selects the output from the synthesis filter device or the sine wave generator for the signal of the lowest frequency subband, and the audio signal of the other subband is selected. An audio decoding device characterized by stopping its output. 6. The audio decoding device according to claim 5, further comprising a level control device, wherein the output level is gradually increased with a constant time constant when returning from error processing. 7. The audio decoding device according to claim 5, further comprising a level control device, wherein the output level is gradually reduced with a constant time constant when outputting a sine wave. 8. A digital wireless microphone system comprising the audio decoding device according to claim 1.