JPH07271391A - Audio decoder - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a speech decoding apparatus capable of preventing deterioration in the quality of reproduced speech due to erroneous detection of an error in speech coding parameters. In a voice decoding device that reproduces a voice signal by performing decoding based on a voice encoding parameter input for each frame, a decoder 1 that decodes the voice encoding parameter.
01, an error detection circuit 102 for detecting an error in a speech coding parameter, storage circuits 104, 105 for storing the decoded speech coding parameter over two frames in which no error is detected, and these storage circuits 104, 105. An interpolation circuit 106 that performs an interpolation calculation of the read speech coding parameters, a speech coding parameter of the frame for which an error is not detected, and a speech code obtained by the interpolation circuit 106 for a frame in which an error is detected. It has a voice synthesizer 108 for reproducing the voice signal by selecting the conversion parameter with the switch 107.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speech decoding apparatus which receives speech coding parameters and decodes and reproduces original speech.

[0002]

2. Description of the Related Art A voice encoding / decoding device used in a mobile communication system such as an automobile telephone is designed to allow a mobile terminal to pass through a place having a low electric field strength such as a valley of a building in addition to a low bit rate. It is required that good audio can be reproduced even if a code error occurs due to the above. Japanese Patent Sho 58-
The speech synthesizer described in Japanese Patent Publication No. 49874 is an example of a conventional speech decoding apparatus proposed to meet such a demand.

FIG. 4 is a block diagram of this conventional speech decoding apparatus. 1 is an input terminal, 2 is an output terminal, 3 is a regenerative relay demodulation circuit, 4 is a synthesis circuit, 5 is a momentary interruption and instantaneous interruption recovery. An instantaneous interruption detection circuit for detecting time, 6 is a delay storage circuit for delaying and storing one set of analysis parameters, and 7 is a switch.

In this conventional apparatus, the received signal input from the input terminal 1 is regeneratively relayed and demodulated by the regenerative relaying demodulation circuit 3, converted into an analysis parameter of a digital signal, and output to the delay storage circuit 6 and the switch 7. When it is not the momentary interruption, the momentary interruption detection circuit 5 detects that it is not the momentary interruption and outputs it to the delay memory circuit 6 and the switch 7. The delay memory circuit 6 is based on the signal from the instantaneous interruption detection circuit 5,
The analysis parameters from the regenerative repeater demodulation circuit 3 are input and sequentially delayed and stored. The switch 7 connects the regeneration relay demodulation circuit 3 and the synthesis circuit 4 based on the signal from the instantaneous interruption detection circuit 5. The synthesizing circuit 4 restores the audio signal based on the output signal of the regenerative repeater demodulating circuit 3 via the switch 7 and outputs it to the output terminal 2.

When a momentary interruption occurs in the input signal from the input terminal 1, the momentary interruption detecting circuit 5 detects it and outputs this information to the delay storage circuit 6 and the switch 7. Delay memory circuit 6
Stops the delayed storage of the input signal from the regenerative relay demodulation circuit 3 based on the instantaneous interruption information from the instantaneous interruption detection circuit 5, and repeatedly outputs the stored contents to the switch 7 in order of oldness. Since the delay memory circuit 6 has a storage capacity of one set of analysis parameters, the analysis parameter of the immediately preceding set is the switch 7.
Is output to. The switch 7 connects the delay storage circuit 6 and the synthesis circuit 4 based on the instantaneous interruption information from the instantaneous interruption detection circuit 5. The synthesizing circuit 4 restores the audio signal based on the input signal from the delay storage circuit 6 and outputs the audio signal to the output terminal 2.
When the instantaneous interruption is restored, the instantaneous interruption detection circuit 5 detects the momentary interruption recovery time and outputs the instantaneous interruption recovery information to the delay storage circuit 6 and the switch 7. At this time, the operation returns to the above-described case when it is not the instantaneous interruption.

As described above, in the conventional speech decoding apparatus, when an error occurs in the speech coding parameter due to the instantaneous interruption of the radio wave, the speech is reproduced based on the one set of speech coding parameters input at the normal time. Even if a code error occurs, it is possible to prevent a significant deterioration in sound quality. However, the detection capability of the instantaneous interruption detection circuit 5 is limited, and erroneous detection may occur regardless of which detection method is used. Therefore, when an error exceeding the detection capability of the instantaneous interruption detection circuit 5 occurs, the sound quality of the reproduced voice may be significantly deteriorated.

[0007]

As described above, in the conventional speech decoding device, since the detection capability of the instantaneous interruption detection circuit is limited, the instantaneous interruption may be erroneously detected, and there is a code error due to the instantaneous interruption. It is possible to detect that there is no error even in a frame that has been opened. In such a case, the voice coding parameter of the frame that is not detected despite the code error is stored, and the voice is reproduced based on this voice coding parameter, so that the sound quality of the decoded voice deteriorates. There was a problem. It is an object of the present invention to provide a voice decoding device capable of preventing deterioration in the quality of reproduced voice due to erroneous detection of an error in a voice encoding parameter.

[0008]

In order to solve the above-mentioned problems, the present invention inputs a voice coding parameter for each predetermined unit section and performs a decoding based on the voice coding parameter to obtain a voice signal. In the audio decoding device for reproduction, an error detecting means for detecting an error in the audio encoding parameter,
Storage means for storing at least one set of speech coding parameters over a plurality of unit sections in which no error is detected by the error detection means, and speech code based on the speech coding parameters for the plurality of unit sections read from the storage means. Parameter reproducing means for reproducing an encoding parameter and a unit section in which an error is not detected by the error detecting means reproduces a voice signal based on a voice encoding parameter of the unit section, and a unit section in which an error is detected by the error detecting means With regard to the above, there is provided a reproducing means for reproducing an audio signal based on the audio encoding parameter reproduced by the parameter reproducing means.

More specifically, as the parameter reproducing means, an interpolating means for interpolating a voice coding parameter over a plurality of unit sections read out from the storing means is provided, and a unit in which an error is detected by the error detecting means. For the section, the audio signal may be reproduced based on the audio encoding parameter obtained by the interpolation means.

Further, in the present invention, a selecting means for selecting the most reliable speech coding parameter among the speech coding parameters over a plurality of unit intervals read out from the storage means is provided, and the error detecting means detects an error. For the detected unit section, the reproduction unit may reproduce the audio signal based on the audio encoding parameter selected by the selection unit.

[0011]

In the speech decoding apparatus according to the present invention, the presence or absence of a code error in the speech coding parameter input by the error detecting means is detected, and in the unit section in which no error is detected, based on the speech coding parameter input. The audio is reproduced by the reproducing means, and at least one set of the audio encoding parameters is stored by the storing means. In this way, the speech coding parameters of a plurality of unit sections in which an error is not detected are stored in the storage means, and the interpolation means performs interpolation calculation on the coding parameters of the plurality of unit sections read from the storage means. Done. Then, in the unit section in which the error is detected, the voice is reproduced based on the voice coding parameter obtained by the interpolation means.

Here, even if an error has occurred in the input voice coding parameter, even if it is detected that there is no error by the error detection of the error detection means, such error detection is performed in two or more units. The probability of continuous occurrence over an interval is very low. Therefore, by performing the interpolation calculation of the voice coding parameters of a plurality of unit sections that are detected as having no error, even if the voice coding parameters of any of the unit sections are erroneous, other unit sections in which no error occurs are generated. As a result of the speech coding parameter mitigating the effect of the error, the reliability of the speech coding parameter obtained by the interpolation calculation is improved, so that the speech is reproduced based on the speech coding parameter of only one unit section. Compared with the conventional method,
The sound quality is significantly reduced.

Further, the reliability of the speech coding parameters of a plurality of unit sections detected as having no error is judged by some means, and the speech coding parameter having the highest reliability is used based on the judgment result. Even if the reproduction is performed, the sound quality deterioration of the reproduced sound is similarly reduced.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is a block diagram of a speech decoding apparatus according to an embodiment of the present invention. The speech decoding apparatus according to this embodiment includes a coding parameter decoder 101 for decoding speech coding parameters input to an input terminal 100, an error detection circuit 102 for detecting an error in input speech coding parameters, and a switch. 103, first and second storage circuits 104 and 105 for storing speech coding parameters of a frame (unit section) detected as “no error” by the error detection circuit 102, and these storage circuits 104 and 105.
The interpolating circuit 106 that performs the interpolating operation of the speech coding parameter read out from, the switch 107 that selects one of the output of the coding parameter decoder 101 and the output of the interpolating circuit 106, and the switch 107 The speech synthesizer 108 synthesizes the original speech from the speech coding parameter, reproduces it, and outputs it to the output terminal 109. The switch 103, the interpolation circuit 106, and the switch 107 are controlled by the output of the error detection circuit 102.

Next, the operation of the speech decoding apparatus according to this embodiment will be described. A plurality of speech coding parameters transmitted from a speech coding device on the transmission side (not shown) are input to the input terminal 100 on a frame-by-frame basis. Taking these speech coding parameters as an example where the coding system of the speech coding apparatus is the CELP (Code Excited Linear Prediction) system, these LPC analysis parameters, drive signal of the synthesis filter, pitch and gain of the voice signal, etc. It is a parameter. Further, these speech coding parameters are error-correction-coded and transmitted.

These speech coding parameters input to the input terminal 100 are decoded by the coding parameter decoder 102 and further output to the switches 103 and 107.

The speech coding parameter input to the input terminal 100 is also input to the error detection circuit 102, and it is detected here whether or not there is a code error. Switch 1
03 and 107 are controlled by the output of the error detection circuit 102. That is, when the output of the error detection circuit 102 indicates “no error”, the switch 107 selects the speech coding parameter decoded by the coding parameter decoder 101 and sends it to the speech synthesizer 108. At this time, the switch 103 is turned on to send the speech coding parameter decoded by the coding parameter decoder 101 to the first storage circuit 104. First memory circuit 104
The second storage circuit 1 stores the contents stored and held until then.
After outputting to 05, the new voice coding parameter input via the switch 103 is stored, and at the same time, the contents stored and held until then are output to the interpolation circuit 106.
On the other hand, the second storage circuit 105 clears the contents stored and held until then, and stores the contents input from the first storage circuit 104.

In this way, the first and second storage circuits 104 and 105 store and hold the speech coding parameters of the frames for which no code error has been detected by the error detection circuit 102 for two frames in ascending order. .

Next, when the output of the error detection circuit 102 indicates that there is an error, the switch 103 is turned off and the speech coding parameter in which the error is detected is input to the storage circuit 104. Blocked and interpolator 1
The first and second storage circuits 104 and 105
Interpolation calculation of the voice encoding parameter is performed based on the contents of Specifically, for example, when the LSP parameter is used as the LPC analysis parameter which is one of the speech coding parameters, the interpolation circuit 106 interpolates the LSP parameter according to the following equation.

Ωi (n) = αωi (n-1) + (1-α) ωi (n-2) (1) where 1 ≦ i ≦ P, P is the analysis order, and ωi (n) is the current LSP parameter of frame, ωi (n-1), ωi
(N-2) are LSP parameters stored and held in the storage circuits 104 and 105, respectively, which are the first and second newest parameters among the LSP parameters of the frame detected as "no error".

Further, α is ωi (n-1) and ωi (-2)
Is a coefficient 0 <α <1 for weighted averaging. More practically, it is set in a range of 0.8 <α <1.
Thus, the weighting coefficient α for ωi (n-1) is set to ωi
The reason for making it larger than the weighting coefficient (α-1) for (n-2) is that ωi (n-1) is temporally closer to the speech coding parameter actually requested as the interpolation calculation result.

The output of the error detection circuit 102 is "in error".
, The speech coding parameter interpolated by the interpolation circuit 106 as described above is the switch 107.
Is selected by and input to the voice synthesizer 108. The voice synthesizer 108 reproduces a voice signal based on the input voice encoding parameter and outputs it to the output terminal 102.

As described above, in this embodiment, for at least one set of speech coding parameters (LSP parameters in the above example) of the frame in which an error has been detected, the parameters of two frames in which no error has been detected in the past are set. The parameters interpolated by weighted average are used instead. As described above, there is a possibility of erroneous detection because the detection capability of the error detection circuit 102 is limited. The reliability of the interpolated parameter is greatly improved by weighted averaging the speech coding parameters of the two frames, and by using this for decoding and reproduction of the speech signal,
It is possible to prevent deterioration of the sound quality of the reproduced voice in the frame in which the code error occurs. Further, in the conventional method, the interpolation of the speech coding parameter is performed based on the parameter of one frame, so to speak, whereas in the present embodiment, the interpolation accuracy is improved because it is performed based on the parameter of two frames. However, the effect of further improving the quality of reproduced voice can be expected.

In the above embodiment, the voice coding parameters of two frames are stored and held, and the parameter of the wrong frame is obtained by quadratic interpolation based on the contents of the voice coding parameters. The number may be increased and higher-order interpolation may be performed. In this case, the effect of erroneous detection of an error can be reduced and the interpolation accuracy can be increased.

(Embodiment 2) FIG. 2 is a block diagram showing the configuration of a decoding apparatus according to another embodiment of the present invention. The same parts as those of the embodiment shown in FIG. 1 are designated by the same reference numerals, and different points will be mainly described. In this embodiment, the point that the interpolation of the voice coding parameters is performed by the moving average is different from the embodiment of FIG. different.

That is, in FIG. 2, the error detection circuit 1
The voice coding parameter decoded by the coding parameter decoder 101 when the output of 02 indicates “no error” is stored and held in the first storage circuit 201. The interpolation circuit 202 includes coefficient multipliers 203 and 204, an adder 205, and a second storage circuit 206. The storage circuit 206 stores and holds the contents in frame units in which the output of the error detection circuit 102 indicates "no error". Controlled as. In the case of this embodiment, the interpolated value of the speech coding parameter is calculated by the following equation.

Ωi = βΩi + (1−β) ωi (n−1) (2) where Ωi is the interpolation value of the LSP parameter, and the adder 2
05 output, ωi (n−1) is the LSP parameter of the frame for which the output of the error detection circuit 102 indicates “no error”, (1−β) is the coefficient of the multiplier 203, and β is the multiplier 20.
4 (coefficient of moving average).

According to the present embodiment, the interpolation of the speech coding parameters is performed by moving averaging the parameters of all frames without error in the past, so that the reliability of the interpolation parameters and the interpolation accuracy are improved. Furthermore, two coefficient multipliers 2
03, 204, adder 205, and one storage circuit 20
Since the high-order interpolation is performed by the interpolation circuit 202 configured by 6, the circuit scale can be reduced as compared with the case where the high-order interpolation is realized by the simple averaging as in the embodiment of FIG. is there.

In each of the above-described embodiments, the interpolation calculation of the voice coding parameter is performed in frame units, but it may be performed in subframe units. In that case, the correlation of the parameters used for the interpolation becomes strong, so that the interpolation accuracy is improved.

(Third Embodiment) FIG. 3 is a block diagram showing the configuration of a speech decoding apparatus according to still another embodiment of the present invention. The same parts as those of the embodiment shown in FIG. 1 are designated by the same reference numerals, and different points will be mainly described. In this embodiment, a reliability determination unit 301 and a switch 302 are provided, and instead of performing interpolation of a voice encoding parameter. , First and second memory circuits 10
1 is that the voice coding parameters stored and held in 4, 105 are selectively used for decoding and reproducing a voice signal.
Is different from the embodiment described above.

First and second memory circuits 104 and 105
Stores the speech coding parameters decoded by the coding parameter decoder 101 when the output of the error detection circuit 102 indicates “no error”. The reliability determination unit 301 determines that one of the speech coding parameters stored and held in the storage circuits 104 and 105, which has better continuity with the past speech coding parameter, has higher reliability, Switch 3 based on the judgment result
Control 02. Then, when the error detection circuit 102 detects that “there is an error”, the voice coding parameter selected by the switch 302 is selected by the switch 107,
Based on this, the voice synthesizer 108 decodes and reproduces the voice.

When selecting the speech coding parameters stored and stored in the storage circuits 104 and 105, in addition to the method of considering the continuity with the past speech coding parameters as described above, Regarding the included filter coefficient, a speech coding parameter including the filter coefficient that makes the filter more stable may be determined to have higher reliability. Regarding the power coefficient included in the speech coding parameter, the speech coding parameter including the power coefficient in which the change from the power coefficient included in the past speech coding parameter changes more smoothly is determined to be more reliable. You may.

As described above, according to the present embodiment, the speech coding parameters of the frame in which the error is detected are the speech codes stored in the plurality of storage circuits 104 and 105 when the error is not detected. By selecting a parameter having the highest reliability among the conversion parameters and using it for audio reproduction, it is possible to prevent deterioration of the sound quality of the reproduced audio of the frame in which the code error has occurred.

[0034]

As described above, according to the present invention, when there is an error in the speech coding parameter, the speech coding is performed based on the speech coding parameters of a plurality of unit sections which are determined to have no error in the past. Is reproduced and output, sound quality deterioration due to erroneous detection of error detection can be prevented, and the sound coding parameter can be accurately interpolated at the time of a code error, so that the reproduced sound quality is improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a speech decoding apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of a speech decoding apparatus according to another embodiment of the present invention.

FIG. 3 is a block diagram showing the configuration of a speech decoding apparatus according to yet another embodiment of the present invention.

FIG. 4 is a block diagram showing the configuration of a conventional speech decoding device.

[Explanation of symbols]

100 ... Input terminal 101 ... Coding parameter decoder 102 ... Error detection circuit 103 ... Switch 104 ... First storage circuit 105 ... Second storage circuit 106 ... Interpolation circuit 107 ... Switch 108 ... Speech synthesizer 109 ... Output terminal 201 ... temporary storage circuit 202 ... interpolation circuit 203 ... coefficient multiplier 204 ... coefficient multiplier 205 ... adder 206 ... storage circuit 301 ... reliability determination unit 302 ... switch

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Emperor Amata 1 Komukai Toshiba-cho, Kouki-ku, Kawasaki-shi, Kanagawa Prefecture Corporate Research & Development Center

Claims (3)

[Claims] 1. A voice decoding device for inputting a voice coding parameter for each predetermined unit section, performing decoding based on the voice coding parameter to reproduce a voice signal, and detecting an error in the voice coding parameter. Error detection means, storage means for storing at least one set of the speech coding parameters over a plurality of unit sections in which no error is detected by the error detection means, and speech over a plurality of unit sections read from the storage means. Parameter reproducing means for reproducing a voice coding parameter based on a coding parameter, and for a unit section in which an error is not detected by the error detecting means, a voice signal is reproduced based on a voice coding parameter of the unit section, and the error is reproduced. The unit section in which the error is detected by the detecting means is reproduced by the parameter reproducing means. A speech decoding apparatus comprising: a reproducing unit that reproduces an audio signal based on the generated audio encoding parameter. 2. A voice decoding device for inputting a voice encoding parameter for each predetermined unit section, performing decoding based on the voice encoding parameter, and reproducing a voice signal, wherein an error of the voice encoding parameter is detected. Error detection means, storage means for storing at least one set of the speech coding parameters over a plurality of unit sections in which no error is detected by the error detection means, and speech over a plurality of unit sections read from the storage means. Interpolation means for performing an interpolation calculation of the coding parameter, and for a unit section in which no error is detected by the error detection means, a voice signal is reproduced based on the voice coding parameter of the unit section, and the error detection means detects the error. A voice signal is generated for the generated unit section based on the voice coding parameter obtained by the interpolation means. A voice decoding apparatus comprising: a reproducing unit for reproducing. 3. A voice decoding apparatus for inputting a voice coding parameter for each predetermined unit section, decoding the voice coding parameter based on the voice coding parameter to reproduce a voice signal, and detecting an error of the voice coding parameter. Error detection means, storage means for storing at least one set of the speech coding parameters over a plurality of unit sections in which no error is detected by the error detection means, and speech over a plurality of unit sections read from the storage means. A selecting means for selecting the most reliable speech coding parameter among the coding parameters and a unit section in which no error is detected by the error detecting means reproduces a speech signal based on the speech coding parameter of the unit section. , The sound selected by the selecting means for the unit section in which the error is detected by the error detecting means. A voice decoding apparatus comprising: a reproduction unit that reproduces a voice signal based on a voice encoding parameter.