JPH08328595A - Speech encoding device - Google Patents

Abstract

PURPOSE: To provide a speech encoding device capable of expressing the part insufficiently expressed by an adaptive code book among a period part of an input speech and improving tone quality of a reproduced speech. CONSTITUTION: In the speech encoding device constituting a speech synthesis filter by linear predictively analyzing the input voice, reproducing the speech based on a code vector stored in the code book and the speech synthesis filter and encoding the speech based on the reproduced voice and the input speech, a pulse code book 7 storing plural kinds of code vectors for a pitch waveform of a voiced sound is provided, and the code vector read out from the pulse code book is made periodic based on an impulse line selected by the retrieval of the impulse line.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speech coding apparatus such as a code driven linear predictive speech coding method (CELP) and a pitch synchronization noise source code excited linear predictive speech coding method (PSI-CELP).

[0002]

2. Description of the Related Art In recent years, low bit rate audio encoding technology has been in the limelight in order to effectively use the radio wave band of car phones and mobile phones and to compress the amount of information in the audio part in multimedia communication. There is.

As this type of speech coding system, a code driven linear predictive speech coding system (CELP: Code Excited Lin) is used.
ear Prediction), pitch synchronization noise source code excitation linear prediction speech coding method (PSI-CELP: Pitch Synchronou)
s Innovation Code ExcitedLinear Prediction) has already been developed.

In the CELP coding system, a linear filter corresponding to the spectral envelope of input speech is constructed by a linear predictive analysis method, and the speech is driven by driving it with a time series code vector stored in a codebook. This is an encoding method for reproduction.

In the PSI-CELP coding system, the CEL
A codebook based on the P coding method
This is a method of driving a linear prediction filter using the candidate vector prepared in Section 1 as the excitation source. The PSI-CELP coding method is characterized in that the excitation source is periodicized in synchronization with the adaptive codebook period corresponding to the pitch period of speech.

FIG. 6 shows an example of a CELP coding device. First, a continuous input voice signal is divided into sections at regular intervals of about 5 to 10 ms. This interval is referred to as a subframe here.

Next, the linear prediction analysis unit 101 performs linear prediction analysis on the input speech in units of subframes to calculate P- _th order linear prediction coefficients α _i (i = 1, 2, ... P). Then, the linear prediction synthesis filter 102 is created based on the obtained linear prediction coefficient α _i .

Next, the adaptive codebook 103 is searched. The adaptive codebook 103 is used to express the periodic component of speech, that is, the pitch.

The output code vector corresponding to the input code of the adaptive codebook 103 has a length (hereinafter referred to as a lag) corresponding to the input code from the rear of the excitation signals of the linear prediction synthesis filter 102 in the previous subframe and before. It is created by segmenting and repeatedly arranging it until the sub-frame length is reached.

The linear predictive synthesis filter 102 is driven by the produced output code vector to produce reproduced voice. Then, after the reproduced voice is subjected to a gain that theoretically minimizes the distance between the input voice and the reproduced voice (distortion of the reproduced voice with respect to the original voice), the distance between the input voice and the reproduced voice is calculated by the distance calculation unit 105. Calculated by

Such an operation is repeated for each input code, and the code of the excitation vector that minimizes the distance is selected.

Thereafter, the noise codebook 104 is searched. The noise codebook 104 is used to represent a variable portion of speech that cannot be represented by the adaptive codebook 103. The noise codebook 104 normally uses white Gaussian noise as a basic tone, and various code vectors each having a length of one subframe (hereinafter referred to as a noise code vector).
Is stored in advance.

First, the noise code vector corresponding to the input code is read from the various noise code vectors stored in the noise code book 104. Next, in order to remove the influence of the code vector selected in the adaptive codebook search, the read noise code vector synthesis filter output is converted to the code vector synthesis filter output selected in the adaptive codebook search. On the other hand, it is made orthogonal to each other and a reproduced voice is created. Then, after the reproduced voice is given a gain such that the distance between the input voice and the reproduced voice is theoretically minimized, the distance between the input voice and the reproduced voice is calculated by the distance calculation unit 1.
Calculated as 05.

Such an operation is repeated for each input code, and the code of the excitation vector that minimizes the distance is selected.

The input code of the adaptive codebook 103 selected by the search of the adaptive codebook 103 and the code representing the gain corresponding thereto, the input code of the noise codebook 104 selected by the search of the noise codebook 104, and the corresponding code The code representing the gain and the linear prediction coefficient are output as the encoded output.

[0016]

Problems to be Solved by the Invention Adaptive Codebook 1
03 efficiently expresses the pitch structure of the voice in the voiced part and the stationary part. However, when there is almost no power of the excitation signal of the previous subframe, when the current subframe is a non-stationary speech such as a rising portion of speech that is composed of a component different from the preceding subframe, the current subframe is In the case of a noisy voice such as an unvoiced part having no pitch period, the adaptive codebook 103 cannot compose an appropriate code vector, which causes a problem that reproduction sound quality is deteriorated.

In order to deal with such a problem, a codebook that outputs a random component is adapted to the adaptive codebook 103.
A method of complementarily preparing is proposed. Like a noise codebook, such a codebook is called a fixed codebook because it has a structure that outputs a code vector that has a fixed correspondence to the input code in every subframe.

The fixed codebook is searched at the same time as the adaptive codebook, and either output vector is exclusively selected according to the minimum distortion criterion. That is, the adaptive codebook and the fixed codebook complement each other and operate as one codebook.

Further, a component which is periodic but cannot be dealt with only by the component of the previous subframe, that is, a non-stationary component of the voiced part which cannot be represented by the adaptive codebook is expressed by the noise codebook with a small distortion. In order to do so, a method of making the noise code vector periodic corresponding to the period of the adaptive code vector has already been proposed.

However, since the code vector stored in the fixed codebook and the noise codebook is a code vector for noise in the first place, whichever method is used, the adaptive codebook of the periodic part of the input speech is used. Sometimes it was not possible to express the parts that were not expressed sufficiently.

According to the present invention, among the periodic parts of the input voice,
It is an object of the present invention to provide a speech coding apparatus capable of expressing a portion that is not sufficiently expressed by an adaptive codebook and improving the sound quality of reproduced speech.

[0022]

A first speech coding apparatus according to the present invention constitutes a speech synthesis filter by performing linear predictive analysis on input speech, and a speech vector and a code vector stored in a codebook are used. In a voice encoding device for reproducing a voice based on a synthesis filter and encoding the voice based on the reproduced voice and an input voice, a pulse code storing a plurality of types of code vectors for a pitch waveform of voiced sound A book is provided, and the code vector read from the pulse codebook is periodicized based on the impulse train selected by the impulse train search.

A second speech coding apparatus according to the present invention is
A codebook including an adaptive codebook that stores a code vector corresponding to a past excitation signal and a noise codebook that stores a code vector for noise by configuring a speech synthesis filter by performing linear predictive analysis on input speech. In a voice encoding device that reproduces a voice based on a code vector read from a voice synthesis filter and a voice synthesis filter, and encodes a voice based on the reproduced voice and an input voice, a plurality of voiced pitch waveforms A pulse codebook in which different types of code vectors are stored is provided in a complementary manner to the noise codebook.When creating a reproduced voice based on the code vector read from the pulse codebook, the input voice A series of impulses in which impulses are generated at different pitch cycle intervals and initial positions are different from each other. Based on the impulse train and the voice synthesis filter, the reproduced voice corresponding to each impulse train is created, and the impulse train with the smallest distortion between the reproduced voice and the input voice is selected and read from the pulse codebook. The encoded code vector is periodicized based on the selected impulse train.

A third speech encoding apparatus according to the present invention is
A means for creating a speech synthesis filter by performing a linear predictive analysis on the input speech, and a plurality of code vectors are sequentially cut out by changing the cutout position from the adaptive codebook in which the code vectors corresponding to the past excitation signals are stored. By driving the speech synthesis filter with each of the code vectors that have been generated to generate reproduced voices corresponding to the respective code vectors that have been cut out, and searching for a code vector that minimizes distortion between the reproduced voice and the input voice. Exploration means,
Also, each code vector is sequentially read from the noise codebook in which a plurality of types of code vectors for noise and the pulse codebook in which a plurality of types of code vectors for the pitch waveform of voiced sound are stored, and each code read out. Second search means for creating a reproduced voice corresponding to each read code vector based on the vector and the voice synthesis filter and searching for a code vector in which the distortion between the reproduced voice and the input voice is the smallest The second search means includes a plurality of impulse trains having different initial positions, which are impulse trains in which impulses are generated at pitch intervals of the input voice when creating the reproduced voice based on the code vector read from the pulse codebook. Based on the type of impulse train and the speech synthesis filter, the replay corresponding to each impulse train Creates each voice, selects the impulse train that minimizes the distortion between the reproduced voice and the input voice, and makes the code vector read from the pulse codebook periodic based on the selected impulse train. It is characterized by having.

A fourth voice encoding device according to the present invention is
A means for creating a speech synthesis filter by performing a linear predictive analysis on the input speech, and a plurality of code vectors are sequentially cut out by changing the cutout position from the adaptive codebook in which the code vectors corresponding to the past excitation signals are stored. By driving the speech synthesis filter with each of the code vectors generated, the reproduced voice corresponding to each code vector that is cut out is created, the distortion between each reproduced voice and the input voice is calculated, and a plurality of types of code vectors are generated. By sequentially reading out the code vector from the fixed codebook in which is stored and driving the voice synthesis filter with the read code vector, the reproduced voice corresponding to each read code vector is created, and the reproduced voice is generated. And the distortion of the input speech are calculated, and the code vector cut out from the adaptive codebook and First search means for searching the code vector read out from the constant codebook for which the distortion calculation result is the minimum, and a noise codebook storing a plurality of code vectors for noise and a pitch waveform of voiced sound From the pulse codebook in which a plurality of types of code vectors are stored, the code vectors are sequentially read, and the reproduced speech corresponding to the read code vectors is read based on the read code vectors and the speech synthesis filter. Respectively, and second search means for searching for a code for a code vector in which the distortion between the reproduced voice and the input voice is minimized, and the second search means is based on the code vector read from the pulse codebook. An impulse train in which impulses are generated at pitch intervals of the input sound when creating a reproduced sound. Create a reproduced voice corresponding to each impulse train based on multiple types of impulse trains whose initial positions are different from each other and a voice synthesis filter, and select the impulse train that minimizes the distortion between the reproduced voice and the input voice. However, it is characterized by comprising means for making the code vector read from the pulse codebook periodic based on the selected impulse train.

[0026]

In the first speech coding apparatus according to the present invention, the pulse codebook in which plural kinds of code vectors for the pitch waveform of voiced sound are stored is provided. The code vector read from the pulse codebook is made periodic based on the impulse train selected by the impulse train search.

In the second speech coding apparatus according to the present invention, the pulse codebook in which plural kinds of code vectors for the pitch waveform of voiced sound are stored is provided in a complementary manner to the noise codebook. The pulse codebook is
Searched simultaneously with the noise codebook, either output vector is exclusively selected by the distortion minimization criterion.

In creating a reproduced voice based on the code vector read from the pulse codebook,
Reproduced voices corresponding to the respective impulse trains are created based on a plurality of types of impulse trains in which impulses are generated at the pitch cycle intervals of the input voice and having different initial positions, and the voice synthesis filter. The impulse train that minimizes the distortion between the reproduced voice and the input voice is selected. Then, the code vector read from the pulse codebook is made periodic based on the selected impulse train.

In the third speech coding apparatus of the present invention, the speech synthesis filter is created by performing the linear predictive analysis on the input speech. From the adaptive codebook in which the code vectors corresponding to the past excitation signals are stored, a plurality of code vectors are sequentially cut out by changing the cutout position, and the cutout is performed by driving the speech synthesis filter with each cutout code vector. The reproduced voice corresponding to each of the generated code vectors is created. Then, the code vector that minimizes the distortion between the reproduced voice and the input voice is searched for.

Further, each code vector is sequentially read out from the noise codebook in which a plurality of types of code vectors for noise are stored and the pulse codebook in which a plurality of types of code vectors for the pitch waveform of voiced sound are stored. Reproduced voices corresponding to the read code vectors are created based on the output code vectors and the voice synthesis filter. Then, the code vector that minimizes the distortion between the reproduced voice and the input voice is searched for.

In creating a reproduced voice based on the code vector read from the pulse codebook,
Reproduced voices corresponding to the respective impulse trains are created based on a plurality of types of impulse trains in which impulses are generated at the pitch cycle intervals of the input voice and having different initial positions, and the voice synthesis filter. The impulse train that minimizes the distortion between the reproduced voice and the input voice is selected. Then, the code vector read from the pulse codebook is made periodic based on the selected impulse train.

In the fourth speech encoding apparatus of the present invention, the speech synthesis filter is created by performing the linear predictive analysis on the input speech. From the adaptive codebook in which the code vectors corresponding to the past excitation signals are stored, a plurality of code vectors are sequentially cut out by changing the cutout position, and the cutout is performed by driving the speech synthesis filter with each cutout code vector. The reproduced voice corresponding to each of the generated code vectors is created. The distortion between each reproduced voice and the input voice is calculated. Further, the code vectors are sequentially read from the fixed codebook in which a plurality of types of code vectors are stored, and the speech synthesis filter is driven by the read code vectors to correspond to the read code vectors. Playback audio is created respectively. The distortion between each reproduced voice and the input voice is calculated. Then, the code vector cut out from the adaptive codebook and the code vector read from the fixed codebook are searched for the one having the smallest distortion calculation result.

Further, each code vector is sequentially read out from the noise codebook in which a plurality of types of code vectors for noise are stored and the pulse codebook in which a plurality of types of code vectors for the pitch waveform of voiced sound are stored. Reproduced voices corresponding to the read code vectors are created based on the output code vectors and the voice synthesis filter. Then, the code vector that minimizes the distortion between the reproduced voice and the input voice is searched for.

In creating a reproduced voice based on the code vector read from the pulse codebook,
Reproduced voices corresponding to the respective impulse trains are created based on a plurality of types of impulse trains in which impulses are generated at the pitch cycle intervals of the input voice and having different initial positions, and the voice synthesis filter. The impulse train that minimizes the distortion between the reproduced voice and the input voice is selected. Then, the code vector read from the pulse codebook is made periodic based on the selected impulse train.

[0035]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a speech coder. In this speech coder, the excitation source of the linear prediction filter consists of two parts. One excitation source consists of an adaptive codebook 4 and a fixed codebook 5, and the other excitation source consists of a noise codebook 6 and a pulse codebook 7.

The adaptive codebook 4 is used to express the periodic component of the voice, that is, the pitch, as described above. The adaptive codebook 4 stores the excitation signal e (adaptive code vector) of the linear prediction filter for a predetermined length in the past.

As described above, the fixed codebook 5 has a structure in which the current subframe has a component different from that of the preceding subframe when there is almost no power of the excitation signal in the preceding subframe. It is provided to complement the adaptive codebook 4 in the case of non-stationary speech, in the case where the current subframe is noisy speech such as an unvoiced part having no pitch period, and the like. The fixed codebook 5 stores various code vectors (fixed code vectors) each having a length corresponding to the sub-frame length.

The noise codebook 6 is used to represent the aperiodic component of speech, as described above. The noise codebook 6 stores various code vectors (noise code vectors) each having a length corresponding to the sub-bram length.

The pulse codebook 7 is used for expressing a part of the periodic part of the input speech which is not sufficiently expressed by the adaptive codebook. FIG. 2 shows an example of a plurality of code vectors (pulse code vectors) stored in the pulse codebook 7. A code vector for a typical pitch waveform of voiced sound is used as each pulse code vector.

The operation of the speech coder will be described below.

A continuous input voice signal is divided into sections having a constant interval of about 40 ms. This interval is referred to as a frame here. Further, the audio signal in one frame is divided into sections having a constant interval of about 8 ms. This interval is referred to as a subframe here.

(1) Creation of Linear Prediction Analysis and Linear Prediction Synthesis Filter First, the linear prediction analysis unit 1 performs a linear prediction analysis on the input speech on a frame-by-frame basis. In this example, the linear prediction analysis unit 1 performs linear prediction analysis twice in one frame, and two 10th-order linear prediction coefficients are obtained by each analysis. Then, based on the obtained linear prediction coefficient, the linear prediction coefficient α _i (i = 1, 2, ..., 10) for each subframe in the one frame is calculated. A linear prediction synthesis filter (speech synthesis filter) 3 is created for each subframe based on the obtained linear prediction coefficient α _i for the subframe.

(2) Pitch Extraction Further, the pitch extraction unit 2 extracts the pitch period Tp of the input voice on a frame-by-frame basis.

(3) Search for Codebook Next, search for adaptive codebook 4 and fixed codebook 5 (adaptive / fixed codebook search) and search for noise codebook 6 and pulse codebook 7 (noise / pulse code). Book search) is performed in subframe units.

(3-1) Adaptive / fixed codebook search

(3-1-1) Distance Calculation by Adaptive Codebook In the adaptive / fixed codebook search, first, distance calculation by the adaptive codebook 4 is performed. In the distance calculation by the adaptive codebook 4, first, the output code vector corresponding to the input code of the adaptive codebook 4 is created as follows.

The excitation signals (adaptive code vectors) of the linear predictive synthesis filter 3 in the preceding subframe and in the preceding subframes stored in the adaptive codebook 4 are divided by the length corresponding to the input code (hereinafter referred to as lag). It is cut out.

If the lag is shorter than the subframe length,
An output code vector is created by repeatedly arranging the cut out adaptive code vectors until the subframe length is reached. When the lag is longer than the subframe length, the output code vector is created by cutting out the length corresponding to the subframe length from the head of the cut out adaptive code vector.

The length (lag) corresponding to each input code is different. The length corresponding to each input code is determined based on the length corresponding to the pitch cycle Tp detected by the pitch extraction unit 2. If the length corresponding to the pitch cycle Tp detected by the pitch extraction unit 2 is L ₀ ,
The length corresponding to each input code is a length selected from a predetermined range centered on L ₀ .

The linear predictive synthesis filter 3 is driven by the produced output code vector to produce reproduced voice. Then, after the reproduced voice is given a gain such that the distance between the input voice and the reproduced voice (distortion of the reproduced voice with respect to the original voice) is theoretically minimized, the distance between the input voice and the reproduced voice is calculated by the distance calculation unit 8. Calculated by After such an operation is repeated for each input code to adaptive codebook 4, fixed codebook 5 performs distance calculation.

(3-1-2) Distance Calculation by Fixed Codebook In the distance calculation by the fixed codebook 5, the fixed code vector corresponding to the input code of the fixed codebook 5 is read. The linear predictive synthesis filter 3 is driven by the read fixed code vector, and reproduced voice is created. Then, after the reproduced voice is given a gain such that the distance between the input voice and the reproduced voice is theoretically minimized, the distance calculation unit 8 calculates the distance between the input voice and the reproduced voice. Such an operation is repeated for each input code to the fixed codebook 5.

In this way, when the distance calculation by the adaptive codebook and the distance calculation by the fixed codebook are performed, the input code of the excitation vector that minimizes the calculated distance and the gain corresponding thereto are selected.

(3-2) Noise / pulse codebook search

(3-2-1) Distance Calculation by Noise Codebook In the noise / pulse codebook search, distance calculation by the noise codebook 6 is first performed. In the distance calculation by the noise codebook 6, the noise code vector corresponding to the input code of the noise codebook 6 is read.
Next, in order to remove the influence of the code vector selected in the adaptive / fixed codebook search, the synthesis filter output of the read noise code vector is the synthesis filter of the code vector selected in the adaptive / fixed codebook search. The output is orthogonalized, and reproduced sound is created.

Then, after the reproduced voice is provided with a gain that theoretically minimizes the distance between the input voice and the reproduced voice, the distance calculation unit 8 calculates the distance between the input voice and the reproduced voice. After such an operation is repeated for each input code to the noise codebook 6, the distance calculation by the pulse codebook 7 is performed.

(3-2-2) Distance Calculation by Pulse Codebook When performing distance calculation by the pulse codebook 7, first, impulse train search is performed.

In this impulse train search, an impulse train is first created based on the pitch period Tp extracted by the pitch extracting unit 2. When the length corresponding to the pitch cycle Tp extracted by the pitch extraction unit 2 is shorter than the subframe length Ts, impulses are generated at the pitch cycle intervals extracted by the pitch extraction unit 2 as shown in FIG. And an impulse train P0 whose total length is equal to the subframe length Ts is created.

Pitch cycle T extracted by the pitch extraction unit 2
When the length corresponding to p is longer than the subframe length Ts, an impulse train P0 composed of one impulse is created as shown in FIG.

Then, a reproduced voice is created based on the impulse train in the same manner as the reproduced voice is created based on the noise code vector read from the noise codebook 6, and the distance to the input voice is calculated. Be done.

As shown in FIG. 3 or 4, such processing is performed on a plurality of impulse trains P0 to Pn having different initial positions of the impulse trains, and the impulse train having the shortest distance is selected.

After that, the distance calculation by the pulse codebook 7 is performed. In the distance calculation by the pulse codebook 7, the pulse code vector corresponding to the input code of the pulse codebook 7 is read. Next, for example, as shown in FIG. 5, the pulse code vector read from the pulse codebook 7 is set at each impulse position of the impulse train (FIG. 5A) selected in the impulse train search. As a result, a pulse code vector (FIG. 5B) having a length corresponding to the subframe length is created.

Next, in order to remove the influence of the code vector selected in the adaptive / fixed codebook search, the synthesized filter output of the pulse code vector generated is the code vector selected in the adaptive / fixed codebook search. The output of the synthesis filter is orthogonalized, and reproduced sound is created.

Then, after the reproduced voice is given a gain that theoretically minimizes the distance between the input voice and the reproduced voice, the distance calculation unit 8 calculates the distance between the input voice and the reproduced voice. Such an operation is repeated for each input code to the pulse codebook 7.

In this way, when the distance calculation by the noise codebook and the distance calculation by the pulse codebook are performed, the input code of the excitation vector that minimizes the calculated distance and the gain corresponding thereto are selected.

An input code of the adaptive codebook or fixed codebook for each subframe selected by the adaptive / fixed codebook search and a code representing the gain corresponding thereto, for each subframe selected by the noise / pulse codebook search The input code of the noise codebook or the pulse codebook and the code representing the corresponding gain, and the two linear prediction coefficients calculated for each frame are output as encoded outputs.

In the above speech coding apparatus, when the current subframe is composed of a component different from that of the preceding subframe, for example, the following operation is considered. That is, when the current subframe is composed of a component different from that of the previous subframe, the input code for the fixed codebook 5 is selected by the adaptive / fixed codebook search of the current subframe, and the noise / pulse codebook The search selects the input code from the pulse codebook 7.

Therefore, the adaptive codebook 4 includes an excitation signal based on the fixed codebook selected by the adaptive / fixed codebook search and an excitation signal based on the pulse codebook selected by the noise / pulse codebook search. The synthesized signal of is newly stored.

Then, in the adaptive / fixed codebook search of the next subframe, the code for the adaptive codebook 4 is selected, and in the noise / pulse codebook search, the code by the noise codebook 6 is selected.

In the above embodiment, since the pulse codebook 7 in which the code vector for the typical pitch waveform of the voiced sound is stored is provided in a complementary manner to the noise codebook 6, the periodic part of the input voice is used. Of these, it is possible to efficiently represent the part that was not sufficiently expressed by the adaptive codebook. As a result, the quality of reproduced voice is improved.

Since the pulse code vector read from the pulse codebook 7 is made periodic so as to correspond to the pitch period of the input voice based on the search result of the simple impulse train, the pulse codebook 7 The processing time for periodicizing the pulse code vector read from is shortened.

In the adaptive / fixed codebook search and the noise / pulse codebook search, the distance is calculated based on the value obtained by passing the difference between the original voice and the reproduced voice through a filter (auditory weighting filter) corresponding to the masking characteristic. You may do it. Further, the distance calculation may be performed based on the difference between the value obtained by passing the original voice through the auditory weighting filter and the value obtained by passing the reproduced voice through the auditory weighting filter.

The perceptual weighting filter is a filter having a characteristic of weighting the distortion of a portion having a large sound power on the frequency axis to be light and the distortion of a portion having a small sound power to be heavy. In addition, the masking characteristic is a characteristic that human hearing makes it difficult to hear sounds of frequencies near a certain frequency component.

[0074]

According to the present invention, since the pulse codebook in which the code vector for the pitch waveform of a typical voiced sound is stored is provided complementarily to the noise codebook, the cycle of the input speech is It is possible to represent a part of the part that is not sufficiently represented by the adaptive codebook. As a result, the quality of reproduced voice is improved.

Further, since the pulse code vector read from the pulse codebook is made periodic so as to correspond to the pitch period of the input voice based on the search result of the simple impulse train, it is read from the pulse codebook. The processing time for periodicizing the emitted pulse code vector is reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a speech encoding apparatus.

FIG. 2 is a schematic diagram showing an example of the contents of a pulse codebook.

FIG. 3 is a schematic diagram showing an example of an impulse train.

FIG. 4 is a schematic diagram showing an example of an impulse train.

FIG. 5 shows an impulse train selected by impulse train search and a pulse code vector created by setting a code vector read from a pulse codebook at each impulse position of the impulse train. It is a schematic diagram.

FIG. 6 is a block diagram showing a conventional example.

[Explanation of symbols]

 1 Linear Prediction Analysis Section 2 Pitch Extraction Section 3 Linear Prediction Synthesis Filter 4 Adaptive Codebook 5 Fixed Codebook 6 Noise Codebook 7 Pulse Codebook 8 Distance Calculation Section

Claims (4)

[Claims] 1. A speech synthesis filter is constructed by performing a linear predictive analysis of input speech, the speech is reproduced based on a code vector stored in a codebook and the speech synthesis filter, and the reproduced speech and the input speech are input. In a speech coder that encodes speech based on speech, a pulse codebook that stores multiple types of code vectors for the pitch waveform of voiced sound is provided, and the impulse train selected by the impulse train search A speech coding apparatus, wherein a code vector read from a pulse codebook is periodicized based on the above. 2. An adaptive codebook for constructing a speech synthesis filter by linearly predicting input speech and storing code vectors corresponding to past excitation signals, and a noise codebook in which code vectors for noise are stored. A code vector read from a codebook including and,
In a voice encoding device that reproduces voice based on a voice synthesis filter and encodes voice based on the reproduced voice and the input voice, a pulse in which a plurality of types of code vectors for a pitch waveform of voiced sound are stored The codebook is provided as a complement to the noise codebook, and when creating the reproduced voice based on the code vector read from the pulse codebook, impulses are generated at the pitch period intervals of the input voice. A reproduced voice corresponding to each impulse train is created based on a plurality of types of impulse trains whose initial positions are different from each other and a voice synthesis filter, and the distortion between the reproduced voice and the input voice is minimized. Impulse train is selected,
The code vector read from the pulse codebook is
A speech coding apparatus characterized in that it is made periodic based on a selected impulse train. 3. A means for creating a speech synthesis filter by performing a linear predictive analysis of input speech, and a plurality of code vectors at different clipping positions from an adaptive codebook in which code vectors corresponding to past excitation signals are stored. Are sequentially extracted, and the speech synthesis filter is driven by each of the clipped code vectors to create a reproduced voice corresponding to each of the clipped code vectors, and the code vector with the smallest distortion between the reproduced voice and the input voice is generated. Each of the code vectors is sequentially searched from a first search means for searching for a noise codebook in which a plurality of types of code vectors for noise are stored and a pulse codebook in which a plurality of types of code vectors for a pitch waveform of voiced sound are stored. Based on the read, each read code vector, and the voice synthesis filter, A second search means for creating reproduced voices corresponding to the respective extracted code vectors and searching for a code vector having the smallest distortion between the reproduced voice and the input voice is provided, and the second search means is a pulse codebook. When creating playback audio based on the code vector read from
Creates and plays back the reproduced voice corresponding to each impulse train based on the impulse trains that generate impulses at the pitch period of the input voice and have different initial positions, and the voice synthesis filter. A speech coding apparatus including means for selecting an impulse train having the smallest distortion between the speech and the input speech and for making the code vector read from the pulse codebook periodic based on the selected impulse train. . 4. A means for creating a speech synthesis filter by performing a linear predictive analysis of input speech, a plurality of code vectors by changing a cut-out position from an adaptive codebook in which code vectors corresponding to past excitation signals are stored. Is sequentially cut out, by driving the speech synthesis filter with each clipped code vector, to create a reproduced voice corresponding to each clipped code vector, and calculate the distortion between each reproduced voice and the input voice,
By sequentially reading code vectors from a fixed codebook that stores multiple types of code vectors and driving the speech synthesis filter with the read code vectors, the reproduced speech corresponding to each read code vector is created. Then, the distortion between each reproduced voice and the input voice is calculated, and the code vector cut out from the adaptive codebook and the code vector read from the fixed codebook are searched for the one having the smallest distortion calculation result. 1 search means, the noise codebook in which a plurality of code vectors for noise is stored, and the pulse codebook in which a plurality of types of code vectors for a pitch waveform of voiced sound are stored Based on each code vector and the speech synthesis filter And a second search means for creating a reproduced voice corresponding to each of the tolls and searching for a code for a code vector having the smallest distortion between the reproduced voice and the input voice. The second search means is read from the pulse codebook. In creating the reproduced voice based on the code vector,
Creates and plays back the reproduced voice corresponding to each impulse train based on the impulse trains that generate impulses at the pitch period of the input voice and have different initial positions, and the voice synthesis filter. A speech coding apparatus including means for selecting an impulse train having the smallest distortion between the speech and the input speech and for making the code vector read from the pulse codebook periodic based on the selected impulse train. .