JP3148920B2 - Audio encoding / decoding device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio encoding / decoding apparatus used for converting an audio signal into a digital signal and transmitting or storing the digital signal.

[0002]

2. Description of the Related Art Conventionally, a speech signal is analyzed for each frame of a predetermined length, separated into a sound source signal and spectral envelope information and encoded, and the encoded data is decoded to generate a speech signal. For example, reference 1 (Takahashi, Iimori, "Vocorder using Vector Quantization of Phase Equalized Sound Source", Hokuriku Chapter Association of IEEJ, B145, P291, October 1992) Are known.

[0003] This conventional example utilizes the fact that a similar waveform is repeated at a pitch cycle when a voice signal is a voiced sound, and the sound source signal of the frame is represented by only one pitch cycle length signal in the frame. The characteristic is that the encoding characteristics of voiced sound parts have been improved by making the sound source signal short-time phase-equalized, thereby stabilizing the extraction of the representative sound source and increasing the efficiency of the vector quantization of the representative sound source. There is an advantage that it can be achieved.

FIG. 4 is a block diagram showing the configuration of the above-mentioned conventional speech coding / decoding apparatus. As shown in the figure,
The speech encoding / decoding device 200 includes an encoding unit 210 and a decoding unit 220. The encoding unit 210 includes a spectrum envelope analysis unit 2, an inverse filter unit 4, a phase equalization unit 7, a representative sound source extraction unit 9, a pitch period extraction unit 11, a voiced / unvoiced determination unit 13, It has a representative excitation coding unit 17. Further, the decoding unit 22
0 represents the representative excitation decoding section 19 and the representative excitation repetition section 21
And a synthesis filter unit 23.

Next, the operation of the above-described conventional speech coding / decoding apparatus 200 will be described. First, the encoding unit 210
Will be described. The spectrum envelope analysis unit 2
The input audio signal S1 is analyzed for each input frame, and the spectral envelope of the audio signal of the corresponding frame is calculated as follows.
For example, it is obtained by a linear prediction analysis method and is output to the inverse filter unit 4 as spectrum envelope information S3. At the same time, the spectrum envelope analyzer 2 encodes the spectrum envelope information S3 and outputs it as a spectrum envelope code S5 to the outside.

[0006] The voiced / unvoiced determination section 13 outputs the input voice signal S
1 is analyzed, for example, to determine whether the input voice signal S1 is a voiced sound or an unvoiced sound, and the result of the determination is output to the pitch period extraction unit 11 as voiced / unvoiced determination information S12. At the same time, the voiced / unvoiced determination unit 13 encodes the voiced / unvoiced determination information S12 and outputs it as a voiced / unvoiced determination code S16 to the outside. When the voiced / unvoiced judgment information S12 is a voiced sound, the pitch cycle extracting unit 11 performs a pitch cycle analysis on the input speech signal S1, and uses the obtained pitch cycle S10 as the representative sound source extracting unit 9.
Output to Further, the pitch period extracting unit 11 simultaneously
The pitch period S10 is encoded and output to the outside as a pitch period code S15.

The inverse filter unit 4 performs, for example, a linear prediction inverse filter process on the input speech signal S 1 using the above-mentioned spectrum envelope information S 3 to obtain a sound source signal S 6, and outputs the sound source signal S 6 to the phase equalization unit 7. The phase equalizer 7 performs a short-time phase equalization process so that the phase of the sound source signal S6 becomes zero at the maximum amplitude position (peak position) on the waveform appearing at the pitch period interval, and the phase equalized sound source signal S8 Is output to the representative sound source cutout unit 9. The representative sound source cutout unit 9 has a pitch cycle S
10 is input, that is, voiced / unvoiced determination information S12
Is a voiced sound, a signal having a length of one pitch period S10 is cut out from the phase-equalized excitation signal S8 based on the position of the maximum amplitude of the phase-equalized excitation signal 8 in the corresponding frame. Representative excitation coding section 17 as excitation S14
Output to The representative excitation coding unit 17 encodes the above-mentioned representative excitation S14 by, for example, vector quantization, and outputs the obtained representative excitation code S18 to the outside.

Next, the operation of the decoding unit will be described.
The representative excitation decoding unit 19 outputs the encoded representative excitation code S
18 and decodes the decoded representative sound source S20 into the representative sound source repetition unit 2.
Output to 1. The representative sound source repetition unit 21 decodes the voiced / unvoiced determination code S16 and the pitch period code S15 into voiced / unvoiced determination information and a pitch period, respectively, and if the voiced / unvoiced determination information is a voiced sound, the pitch period The decoded representative excitation S20 is repeated at intervals of to generate a decoded excitation signal S27,
Output to the synthesis filter 23. If the voiced / unvoiced determination information is unvoiced, white noise is generated and output to the synthesis filter 23 as a decoded excitation signal S27. The synthesis filter unit 23 decodes the spectrum envelope from the spectrum envelope code S5, and synthesizes the decoded speech signal S28 from the decoded spectrum envelope and the decoded excitation signal S27 by, for example, a linear prediction synthesis filter technique.

[0009]

However, in the conventional speech encoding / decoding apparatus 200 as shown in FIG. 4, the representative excitation repetition section 21 of the decoding section 220 simply converts the decoded representative excitation S20 to the pitch period. Since the decoded excitation signal S27 of the corresponding frame is repeatedly generated at intervals, the decoded excitation signal suddenly changes at the frame boundary if the shape of the decoded representative excitation of the relevant frame and the frame immediately before and after is different to some extent or more. As a result, there is a problem that the sound quality of the decoded audio signal is deteriorated (such as abnormal noise due to a sudden change).

This will be described with reference to FIG. FIG.
5A and 5B are diagrams illustrating generation of a decoded excitation signal by simple repetition of a decoded representative excitation in the above-described conventional speech encoding / decoding apparatus. FIG. 5A illustrates a representative excitation, and FIG. Is shown. As shown in the figure, if the shape of the decoded representative sound source of the corresponding frame M is different from that of the immediately preceding and succeeding frames (M-1) and (M + 1), the frame boundaries B3 and B3
In FIG. 4, the decoded excitation signal suddenly changes, and as a result, the sound quality of the decoded audio signal deteriorates (such as abnormal noise due to a sudden change).

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and it is possible to generate a decoded excitation signal with good continuity even if the corresponding representative frame and the immediately preceding and succeeding frames have different decoded representative excitations. It is an object of the present invention to provide a speech encoding / decoding device capable of obtaining a good decoded speech signal.

[0012]

According to a first aspect of the present invention, an input audio signal is analyzed for each frame of a predetermined length, and spectral envelope information of the input audio signal and a sound source are analyzed. A signal and a pitch period are obtained, and when the input voice signal is a voiced sound, short-time phase equalization is performed so that the phase of the sound source signal becomes zero at the maximum amplitude position on the signal waveform appearing at the pitch period interval. An encoding unit that extracts a representative sound source for one pitch period length after performing the process, encodes the representative sound source, the pitch period, and the spectrum envelope information, and outputs the information as a spectrum envelope code;
The coded parameters output from the coder are decoded, and when the input voice signal is a voiced sound, the decoded representative sound source having one pitch cycle length is arranged at intervals of the pitch cycle. And a decoding unit that generates a decoded excitation signal and decodes the decoded audio signal using the decoded excitation signal and the decoded spectrum envelope. Sound source shaping means for weighting and adding the representative sound source and the impulse signal of the corresponding frame; and representative sound source repetition for generating the decoded sound source signal by arranging the shaped representative sound sources output from the sound source shaping device at intervals of the pitch period. And means in the decoding unit.

According to a second aspect of the present invention, in the audio encoding / decoding apparatus according to the first aspect, the sound source shaping means is configured to determine a change in an audio signal of the corresponding frame and a frame near the corresponding frame. It is configured to change the value of a weighting coefficient when weighting and adding the representative sound source and the impulse signal according to the magnitude.

[0014]

According to the first aspect of the present invention, the sound source shaping means weights and adds the representative sound source and the impulse signal of the decoded frame. In addition, the representative excitation repeating unit generates the decoded excitation signal by arranging the shaped representative excitations output from the excitation shaping unit at intervals of the pitch period.

According to the second aspect of the present invention having the above structure, the sound source shaping means may be configured to set the representative sound source and the representative sound source in accordance with a magnitude of a change in an audio signal between the relevant frame and a frame near the relevant frame. The value of the weighting coefficient when weighting and adding the impulse signal is changed.

[0016]

【Example】

(First Embodiment) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a speech encoding / decoding device according to a first embodiment of the present invention. As shown in the figure, the speech encoding / decoding device 101 includes an encoding unit 110 and a decoding unit 120. The encoding unit 110 includes a spectrum envelope analysis unit 2, an inverse filter unit 4, a phase equalization unit 7, and a representative sound source extraction unit 9
, Pitch period extracting unit 11, voiced / unvoiced determining unit 13
And a representative excitation coding unit 17. The decoding section 120 includes a representative excitation decoding section 19, a representative excitation repetition section 21, an excitation shaping section 25, and a synthesis filter section 2.
3. The difference between the speech encoding / decoding device 101 of the first embodiment and the speech encoding / decoding device 200 of the conventional example described above is that
20 in that a sound source shaping unit 25 as a sound source shaping means is provided. The sound source shaping unit 25 is arranged on the output side of the representative sound source decoding unit 19 and on the input side of the representative sound source repetition unit 21 which is a representative sound source repetition unit. The components other than the sound source shaping unit 25 have the same functions and effects as those of the components shown in FIG. 4, and therefore, are denoted by the same reference numerals as those of the components shown in FIG. 4, and description thereof will be omitted.

The speech encoding / decoding device 101 will be described below.
Will be described. The sound source shaping section 25 shapes the representative sound source S20 by weighting and adding the impulse signal to the representative sound source S20. Due to this shaping, the shaped waveform of the shaped representative sound source S26 always approaches the impulse.
Even if this is repeated in the representative excitation repeating section 21, a decoded excitation signal S22 having a smooth change can be generated. If the input audio signal changes greatly between the current frame and its neighboring frames, adjust the above weighting coefficient to make the representative sound source closer to the impulse, thereby smoothing the change of the sound source signal. Can be.

Hereinafter, the operation of the sound source shaping section 25 will be described.
This will be described in more detail. Here, the representative sound source sound S20 is RC
i (i is a positive integer from 1 to P), an impulse signal having a pulse at the same position as the maximum amplitude position of the representative sound source S20 is RIi, a pitch period is P, and a weighting coefficient is α (α is 0 When ≦ α ≦ 1 (real number), the sound source shaping unit 25 weights and adds the two according to, for example, the following formula: RMi = (1−α) × RCi + α × RIi (1) A certain signal RMi is obtained.

In the above equation (1), the following equation

(Equation 1) There is a relationship.

FIG. 2 is a diagram for explaining the operation of weighted addition of the representative sound source represented by the above equation (1) in the sound source shaping section 25. As shown in the figure, it is shown that a shaped representative sound source that approaches the shape of the impulse waveform can be obtained.

The sound source shaping section 25 decodes the spectrum envelope code S5 to obtain a spectrum envelope, and calculates a distance D between the spectrum envelope of the current frame and the spectrum envelope of the immediately preceding frame. Sets a large weighting coefficient α to make the shaped representative sound source closer to an impulse.

The representative excitation repetition section 21 repeats the shaped representative excitation S26 obtained by the excitation shaping section 25 at a pitch cycle interval to obtain a decoded excitation signal S22.

FIG. 3 shows an example of the decoded excitation signal S22 generated in this embodiment. FIG. 5A shows a shaped representative excitation, and FIG. 5B shows a decoded excitation signal. I have. As shown in the figure, a decoded excitation signal having a smooth change between frames is obtained by the processing of the excitation shaping section 21.

(Second Embodiment) In the first embodiment described above,
Although the sound source shaping unit 25 uses the distance value D between the spectral envelopes of the current frame and the immediately preceding frame to set the magnitude of the weighting coefficient α, the present invention is not limited to this.
It may be configured as in the second embodiment using the cross-correlation values of the representative sound sources of both frames.

The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the claims of the present invention, and any device having the same function and effect can be realized by the present invention. It is included in the technical scope of the invention.

[0026]

As described above, according to the present invention, since the representative sound source is shaped by the sound source shaping means so as to approximate an impulse, a decoded sound source signal having a smooth change between frames can be obtained. Further, when the change of the input speech signal is large, the input speech signal is shaped so as to be closer to the impulse, so that a decoded excitation signal that can follow a large change can be obtained. Therefore, there is an advantage that a high-quality decoded audio signal can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a speech encoding / decoding device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an operation of a sound source shaping unit in the speech encoding / decoding device illustrated in FIG.

FIG. 3 is a diagram for explaining an operation of generating a decoded excitation signal in the speech encoding / decoding apparatus shown in FIG.

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

5 is a diagram illustrating an operation of generating a decoded excitation signal in the speech encoding / decoding device illustrated in FIG. 5;

[Explanation of symbols]

 2 Spectrum Envelope Analysis Unit 4 Inverse Filter Unit 7 Phase Equalization Unit 9 Representative Sound Source Extraction Unit 11 Pitch Period Extraction Unit 13 Voiced / Unvoiced Judgment Unit 17 Representative Sound Source Coding Unit 19 Representative Sound Source Decoding Unit 21 Representative Sound Source Repetition Unit 23 Synthesis Filter Unit 25 sound source shaping unit 101 voice coding / decoding device 110 coding unit 120 decoding unit 200 voice coding / decoding device 210 coding unit 220 decoding unit S signal, etc.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-250694 (JP, A) JP-A-61-51200 (JP, A) JP-A-60-260098 (JP, A)

Claims (2)

(57) [Claims] 1. An input audio signal is analyzed for each frame of a predetermined length to obtain spectrum envelope information, a sound source signal, and a pitch period of the input audio signal, and when the input audio signal is a voiced sound, After performing a short-time phase equalization process so that the phase of the sound source signal becomes zero at the maximum amplitude position on the signal waveform appearing at the pitch period interval, a representative sound source for one pitch period length is extracted. An encoding unit that encodes the sound source and the pitch cycle and the spectrum envelope information and outputs the encoded information as a spectrum envelope code, and decodes each encoded parameter output from the encoding unit,
When the input audio signal is a voiced sound, a decoded excitation signal is generated by arranging the decoded representative excitation having one pitch cycle length at intervals of the pitch cycle,
A decoding unit that decodes the decoded speech signal using the decoded excitation signal and the decoded spectrum envelope, wherein the representative excitation and the impulse signal of the decoded corresponding frame are Sound source shaping means for weighting and adding, and representative sound source repetition means for generating the decoded excitation signal by arranging shaped representative sound sources output from the sound source shaping means at intervals of the pitch period, provided in the decoding unit. Speech encoding / decoding device. 2. The sound source shaping means includes: a weighting coefficient value for weighting and adding the representative sound source and the impulse signal according to the magnitude of a change in an audio signal between the relevant frame and a frame near the relevant frame. 2. The speech encoding / decoding apparatus according to claim 1, wherein