JP3276356B2 - CELP-type speech coding apparatus and CELP-type speech coding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a CELP-type speech decoding apparatus and a CELP-type speech decoding method for efficiently encoding / decoding speech information.

[0002]

2. Description of the Related Art Conventional speech coding techniques include Code E
xcited Linear Prediction: "High Quality Speech at
Low Bit Rate ", MR Schroeder, Proc. ICASSP'85, p
There is a CELP speech coding apparatus described in p.937-940 (Reference 1). This speech coding apparatus performs linear prediction for each frame obtained by dividing an input speech at a fixed time, and stores a prediction residual (excitation signal) by the linear prediction for each frame with an adaptive codebook storing past driving sound sources. Is a device that performs encoding using a random codebook that stores the random code vector of.

First, the conventional CELP speech coding apparatus will be described in detail with reference to FIG.

[0004] A linear prediction analysis unit 12 analyzes the speech signal 11 input to the CELP speech coding apparatus and calculates a linear prediction coefficient. Here, the linear prediction coefficient is a parameter representing the envelope characteristic of the frequency spectrum of the audio signal.
The linear prediction coefficients obtained by the linear prediction analysis unit 12 are quantized by the linear prediction coefficient encoding unit 13 and then sent to the linear prediction coefficient decoding unit 14. Note that the quantization number obtained at this time is output to the code output unit 24 as a linear prediction code. The linear prediction coefficient decoding unit 24 decodes the linear prediction coefficients quantized by the linear prediction coefficient encoding unit 13 to obtain coefficients of a synthesis filter, and outputs the coefficients to the synthesis filter 15.

[0005] The adaptive codebook 17 is a codebook that outputs a plurality of types of adaptive code vector candidates, and is composed of a buffer that stores driving excitations for the past several frames. Note that the adaptive code vector is a time-series vector expressing a periodic component in the input speech.

The random codebook 18 is a codebook storing a plurality of random code vector candidates (types corresponding to the number of assigned bits). Note that the noise code vector is a time-series vector representing an aperiodic component in the input speech.

The adaptive code gain weighting section 19 and the noise code gain weighting section 20 provide an adaptive code gain read from the weight codebook 21 for each of the candidate vectors output from the adaptive codebook 17 and the noise codebook 18, respectively. The noise signals are multiplied by the noise code gains, respectively, and output to the addition unit 22. Note that the weighting codebook is a memory that stores a plurality of types of weights (types corresponding to the number of allocated bits) for weights for multiplying adaptive code vector candidates and weights for multiplying noise code vector candidates.

The adder 22 adds the adaptive code vector candidates and the noise code vector candidates weighted by the adaptive code gain weighting unit 19 and the noise code gain weighting unit 20, respectively, to generate a driving excitation vector candidate, and Output to The synthesis filter 15 is an all-pole filter composed of the coefficients of the synthesis filter obtained by the linear prediction coefficient decoding unit 14, and outputs a synthesized speech vector candidate when a driving excitation vector candidate is input from the addition unit 22. It has the function to do.

The distortion calculator 16 calculates the distortion between the synthesized speech vector candidate output from the synthesis filter 15 and the input speech 11, and outputs the obtained distortion value to the code number identification unit 23. The code number identification unit 23 converts three types of code numbers (adaptive code number, noise code number, and weight code number) that minimize the distortion calculated by the distortion calculation unit 16 into three types of code books (adaptive code book). , Noise codebook, weight codebook). The three types of code numbers specified by the code number specifying unit 23 are output to the code output unit 24. The code output unit 24 collects the linear prediction code number obtained by the linear prediction coefficient coding unit 13 and the adaptive code number, the noise code number, and the weight code number specified by the code number specification unit 23, and sends the result to the transmission path. Output.

Next, the operation of the conventional CELP speech decoding apparatus will be described with reference to FIG. In the audio decoding device (FIG. 7), first, the code input unit 31
Receive the code transmitted from, and decompose the code into a linear prediction code number corresponding to the received code, an adaptive code number, a noise code number, and a weight code number, and decode the codes obtained by the decomposition into linear prediction coefficient decoding, respectively. To the coding unit 32, the adaptive codebook 33, the noise codebook 34, and the weight codebook 35.

Next, a linear prediction coefficient decoding unit 32 decodes the linear prediction code number obtained by the code input unit 31 to obtain a coefficient of a synthesis filter, and outputs it to the synthesis filter 39. Then, an adaptive code vector is read from a position corresponding to the adaptive code number in the adaptive code book, a noise code vector corresponding to the noise code number is read from the noise code book, and a weight code number is read from the weight code book. The adaptive code gain and the noise code gain corresponding to are read out. Then, the adaptive code vector weighting unit 36 multiplies the adaptive code vector by the adaptive code gain and sends the result to the adding unit 38. Similarly, the noise code vector weighting unit 37 multiplies the noise code vector by the noise code gain, and
Sent to

The adder 38 adds the two code vectors to generate a driving excitation vector, and the generated driving excitation is combined with the adaptive codebook 33 for updating the buffer and for driving the filter. It is sent to the filter 39.
The synthesis filter 39 is driven by the driving sound source vector obtained by the addition unit 38, and reproduces a synthesized voice using the output of the linear prediction coefficient decoding unit 32.

The distortion calculator 16 of the CELP speech coding apparatus generally calculates a distortion E obtained by the following (Equation 1).

[0014]

(Equation 1)

Here, in order to minimize the distortion E in (Equation 1), the distortion is calculated in a closed loop for all combinations of the adaptive code number, the noise code number, and the weight code number, and each code number is specified. Is ideal. However, since the amount of calculation processing becomes too large when a closed loop search of (Equation 1) is performed, generally, first, an adaptive code number is specified by vector quantization using an adaptive codebook, and then a noise codebook is used. The noise code number is specified by the vector quantization, and finally the weight code number is specified by the vector quantization using the weight codebook. Here, in this case, the vector quantization processing using the random codebook will be described in more detail.

When the adaptive code number and the adaptive code gain are determined first or tentatively, the equation for evaluating distortion in (Equation 1) is transformed into the following (Equation 2).

[0017]

(Equation 2)

However, the vector x in (Equation 2) is the noise source information (noise code number) obtained by the following (Equation 3) using the adaptive code number and the adaptive code gain specified earlier or provisionally. (Specific target vector).

[0019]

(Equation 3)

When the noise code gain gc is specified after the noise code number is specified, it can be assumed that gc in (Equation 2) can take an arbitrary value. It is generally known that the process of specifying the vector number (the vector quantization process of the noise excitation information) can be replaced by the specification of the number of the noise code vector that maximizes the following fractional expression (Equation 4).

[0021]

(Equation 4)

That is, when the adaptive code number and the adaptive code gain are specified in advance or provisionally,
The vector quantization process of the noise source information means the distortion calculation unit 1
This is a process of specifying the number of the noise code vector candidate that maximizes the fractional expression of (Equation 4) calculated in (6).

In the early CELP encoder / decoder, a random number sequence of a type corresponding to the number of allocated bits was stored in a memory and used as a random codebook. However, there is a problem that a very large memory capacity is required and the amount of calculation processing for calculating the distortion of (Equation 4) for each of the noise code vector candidates becomes enormous.

Conventionally, one method of solving this problem is to use “8KBIT / S ACELP CODING OF SPEECH WITH 10 MS SPE”.
ECH-FRAME: A CANDIDATE FOR CCITT STANDARDIZATIO
N ": R. Salami, C. Laflamme, JP. Adoul, ICASSP'94,
As described in pp. II-97 to II-100, 1994 (Document 2), etc., a CELP speech encoding apparatus / decoding apparatus using an algebraic excitation vector generation unit that generates excitation vectors algebraically. No.

[0025]

However, in a CELP speech coding apparatus / decoding apparatus using the algebraic excitation generating section as a noise codebook, the noise excitation information (noise code number identification) obtained by (Equation 3) is used. ) Is always approximated by a small number of pulses, so there is a limit in improving speech quality. This is apparent from the fact that when the element of the noise source information x in (Equation 3) is actually examined, it hardly consists of only a small number of pulses.

According to the present invention, there is provided a new diffusion method capable of generating a sound source vector having a shape which is statistically highly similar to the shape of a sound source vector obtained when an audio signal is actually analyzed.
CELP-type speech that can obtain higher quality synthesized speech by using a vector generator for a noise codebook than when using a conventional algebraic excitation generator as a noise codebook
An object of the present invention is to provide an encoding device and a CELP type speech encoding method .

[0027]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a linear prediction method for performing linear prediction analysis on an input speech signal.
Measurement and analysis means and a random codebook for generating a random code vector
And the synthesized speech vector
CELP speech code having synthesis filter for generating
A randomizer, wherein the random codebook includes a plurality of channels.
A pulse vector generator supplies a pulse vector from algebraic codebook having a selection section for selecting a spreading pattern storing unit for storing a plurality of diffusion patterns, any of the plurality of diffusion patterns stored, supplied The said pulse
Vector and the selected diffusion pattern for each channel
Vector that is convolved with and output as a diffusion vector
And a diffusion vector generation device having a
Is done. Thereby, it is possible to generate a sound source vector having a shape very similar to the shape of the actual sound source vector,
Therefore, a CELP-type speech encoding device capable of outputting higher quality synthesized speech is obtained.

[0028]

[0029]

[0030]

[0031]

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS.

(Embodiment 1) FIG. 1 is a block diagram showing a configuration of a sound source vector generating apparatus according to the present embodiment. In FIG. 1, reference numeral 101 denotes N channels for generating a vector (hereinafter, referred to as a pulse vector) in which a unit pulse with a polarity rises in a certain element on the vector axis (in the present embodiment, N = 3) The pulse vector generation unit 102 provided includes M types for each of the N channels (this embodiment describes a case where M = 2).
A diffusion pattern storage / selection unit 103 having both a function of storing the diffusion pattern of the above and a function of selecting one type of the diffusion pattern from the stored M types of diffusion patterns, and a pulse 103 output from the pulse vector generation unit 101 A pulse vector spreading unit having a function of performing a superposition operation of a vector and a spreading pattern selected from the spreading pattern storage / selection unit 102 for each channel to generate N spreading vectors, 104 is the pulse vector spreading unit 103 A diffusion vector adding unit 105 having a function of generating a sound source vector by adding the N diffusion vectors generated by the above-mentioned is a generated sound source vector. In the present embodiment, a case will be described where the pulse vector generation unit 1 algebraically generates N (N = 3) pulse vectors according to the rules described in (Table 1) below.

[0034]

[Table 1]

The operation of the sound source vector generation device configured as described above will be described with reference to FIG. The spreading pattern storage / selection unit 102 selects one type from the two types of spreading patterns stored for each channel, and outputs the selected one to the pulse vector spreading unit 103. Here, it is assumed that numbers are assigned corresponding to the selected combinations of the diffusion patterns (total number of combinations: M ： N = 8). Next, the pulse vector generation unit 101 algebraically generates pulse vectors for the number of channels (three in this embodiment) according to the rules described in (Table 1).

The pulse vector spreading section 103 uses the spreading pattern selected by the spreading pattern storing / selecting section 102 and the pulse generated by the pulse vector generating section 101 in a superposition operation by the following (Equation 5). A spreading vector is generated for each channel.

[0037]

(Equation 5)

The spreading vector adding section 104 adds the three spreading vectors generated by the pulse vector spreading section 103 to
The sound source vector 105 is generated by the addition according to the following (Equation 6).

[0039]

(Equation 6)

In the sound source vector generation device configured as described above, the combination of the diffusion pattern selected by the diffusion pattern storage / selection unit and the change in the position and polarity of the pulse in the pulse vector generated by the pulse vector generation unit are determined. By having them, it becomes possible to generate various sound source vectors. In the thus configured sound source vector generation apparatus, the combination of the diffusion patterns selected by the diffusion pattern storage / selection unit 102 and the shape of the pulse vector (pulse position and pulse polarity) generated by the pulse vector generation unit 101 1 for each of the two types of information
It is possible to assign a number corresponding to one to one. Further, the diffusion pattern storage / selection unit 102 can perform learning in advance based on actual sound source information and store a diffusion pattern obtained as a result of the learning.

If the above excitation vector generation device is used for the excitation information generation unit of the speech encoding device / decoding device, the combination number of the diffusion pattern selected by the diffusion pattern storage / selection unit and the pulse vector generation unit By transmitting two types of numbers, that is, the combination number of the pulse vector (which can specify the pulse position and the pulse polarity), transmission of noise source information can be realized.

Further, the use of the sound source vector generation unit configured as described above makes it possible to generate a sound source vector having a shape (characteristic) similar to actual sound source information, compared to the case of using a pulse sound source generated algebraically. Becomes possible.

In this embodiment, the case where the diffusion pattern storage / selection unit 102 stores two types of diffusion patterns per channel has been described. However, other than two types of diffusion patterns are stored for each channel. If you do,
Similar functions and effects can be obtained.

In this embodiment, the case where the pulse vector generation unit 101 has a three-channel configuration and is based on the pulse generation rules described in Table 1 has been described. Even when pulse generation rules other than those described in (Table 1) are used as rules,
Similar functions and effects can be obtained.

Further, by constituting an audio signal communication system or an audio signal recording system having the above-mentioned excitation vector generation device or the audio encoding / decoding device, it is possible to obtain the functions and effects of the above-mentioned excitation vector generation device. Can be.

(Embodiment 2) FIG. 2 is a block diagram showing the configuration of a CELP speech encoding apparatus according to the present embodiment.
FIG. 3 is a block diagram showing the configuration of the CELP-type speech decoding apparatus.

FIG. 2 shows a case where the excitation vector generation apparatus (FIG. 1) described in the first embodiment is applied to the noise codebook (18 in FIG. 6) of the conventional CELP speech coding apparatus. Is obtained by applying the excitation vector generation apparatus described in the first embodiment to the noise codebook (34 in FIG. 7) of the conventional CELP speech coding apparatus. Therefore, processes other than the vector quantization process of the noise source information are the same as those described in the section of the related art. In the present embodiment, the vector quantization process of the noise source information in FIGS. , A speech encoding device and a speech decoding device will be described. Further, as in the first embodiment, the number of channels N = 3, the number of diffusion patterns of one channel M = 2, and the generation of the pulse vector is based on (Table 1).

In the vector quantization process of the noise source information in the speech coding apparatus of FIG. 2, two kinds of numbers (a combination number of a diffusion pattern, a pulse position and a pulse polarity) that maximize the reference value of (Equation 4) are used. (Combination number). When the excitation vector generation apparatus of FIG. 1 is used as a noise codebook, the combination number (8 types) of the diffusion pattern and the combination number of the pulse vector (when the polarity is considered: 16)
384 types) in a closed loop, the diffusion pattern storage / selection unit 215 first selects one of the two types of diffusion patterns stored by itself, and generates a pulse vector. Output to the diffusion unit 217.
After that, the pulse vector generation unit 216 algebraically generates pulse vectors for the number of channels (three in this embodiment) according to the rules described in (Table 1), and outputs the generated pulse vectors to the pulse vector spreading unit 217. The pulse vector spreading section 217
A diffusion vector is generated for each channel by using the diffusion pattern selected by the diffusion pattern storage / selection unit 215 and the pulse vector generated by the pulse vector generation unit 216 in a superposition operation by (Equation 5). Diffusion vector adder 2
Reference numeral 18 adds a diffusion vector obtained by the pulse vector spreading section 217 to generate a sound source vector (a candidate for a noise code vector). Then, the distortion calculation unit 206
Calculates the value of (Equation 4) using the noise code vector candidate obtained by the spreading vector addition unit 218. The calculation of the value of (Equation 4) is performed for all combinations of pulse vectors generated according to the rules described in (Table 1), and the combination number of the diffusion pattern when the value of (Equation 4) is maximized from among them , The combination number of the pulse vector (combination of the pulse position and its polarity) and the maximum value at that time are output to the code number specifying unit 213.

Next, the diffusion pattern storage / selection unit 215
From the stored diffusion patterns, a different combination of diffusion patterns is selected. Then, for the newly selected combination of diffusion patterns, the value of (Equation 4) is calculated for all combinations of pulse vectors generated by the pulse vector generation unit 216 according to the rules of (Table 1) in the same manner as described above. Then, from among them, the combination number of the diffusion pattern, the combination number of the pulse vector, and the maximum value when maximizing (Equation 4) are output to the code number specifying unit 213 again.

This processing is performed by the diffusion pattern storage / selection unit 21
5 is repeated for all combinations that can be selected from the diffusion patterns stored (the total number of combinations is 8 in the description of the present embodiment).

The code number specifying section 213 is provided for the distortion calculating section 20.
Compare the maximum value of a total of 8 calculated by 6
The largest one is selected from them, and two kinds of combination numbers (combination number of the diffusion pattern and combination number of the pulse vector) at the time when the maximum value is generated are specified, and are sent to the code output unit 214 as the noise code number. Output.

On the other hand, in the speech decoding apparatus of FIG. 3, code input section 301 receives a code transmitted from speech encoding apparatus (FIG. 2), and converts the received code into a corresponding linear prediction code number and an adaptive linear prediction code number. A code number, a noise code number (consisting of two types, a combination number of a spreading pattern and a combination number of a pulse vector), and a weighting code number, and codes obtained by the decomposition are respectively decoded by linear prediction coefficients. Conversion part 30
2. Output to adaptive codebook 303, noise codebook 304, and weight codebook 305. Here, among the noise code numbers,
The combination number of the diffusion pattern is stored in the diffusion pattern storage / selection unit 31.
1, and the combination number of the pulse vector is output to the pulse vector generation unit 312.

Then, the linear prediction coefficient decoding unit 302 decodes the linear prediction code number to obtain the coefficients of the synthesis filter,
Output to the synthesis filter 309. In the adaptive codebook 303, an adaptive code vector is read from a position corresponding to the adaptive code number.

In the noise codebook 304, the spread pattern is stored.
The selecting unit 311 reads out a spreading pattern corresponding to the combination number of the spreading pulse for each channel, and outputs it to the pulse vector spreading unit 313. The pulse vector generating unit 312 converts the pulse vector corresponding to the combination number of the pulse vector into the number of channels. The pulse pattern is generated and output to the pulse vector spreading unit 313. The pulse vector spreading unit 313 superimposes the diffusion pattern received from the diffusion pattern storage / selection unit 311 and the pulse vector received from the pulse vector generation unit 312 according to (Equation 5). A diffusion vector is generated using the calculation and output to the diffusion vector addition unit 314. The spreading vector adding section 314 adds the spreading vector of each channel generated by the pulse vector spreading section 313 to generate a noise code vector.

Then, an adaptive code gain and a noise code gain corresponding to the weight code number are read from the weight codebook 305, and the adaptive code vector weighting unit 306 multiplies the adaptive code vector by the adaptive code gain. The code vector weighting unit 307 multiplies the noise code vector by the noise code gain and sends the result to the addition unit 308.
The adder 308 adds the two code vectors multiplied by the gain to generate a driving excitation vector, and transmits the generated driving excitation vector to the adaptive codebook 303 for updating the buffer, and also drives the synthesis filter. Output to the synthesis filter 309 in order to perform the processing.

The synthesis filter 309 is driven by the driving sound source vector obtained by the adding section 308, and reproduces the synthesized speech 310. Adaptive codebook 303 updates the buffer with the driving excitation vector received from adding section 308.

However, in the diffusion pattern storage / selection unit in FIGS. 2 and 3, the sound source vector described in (Equation 6) is substituted for c in (Equation 2), and the following distortion evaluation criterion equation (Equation 7) is used. Is a cost function, and it is assumed that a diffusion pattern obtained by learning in advance so that the value of the cost function becomes smaller is stored for each channel. By doing this,
Since it becomes possible to generate a source vector having a shape similar to the shape of actual noise source information (vector x in (Equation 4)), CELP speech using an algebraic source vector generator for a noise codebook It is possible to obtain higher quality synthesized speech than the encoder / decoder.

[0058]

(Equation 7)

In the present embodiment, the diffusion pattern storage / selection unit selects M diffusion patterns obtained by learning in advance so as to reduce the value of the cost function described in (Equation 7) for each channel. Although the case where each of them is stored has been described, in practice, it is not necessary that all M diffusion patterns are obtained by learning, and at least one type of diffusion pattern obtained by learning is provided for each channel. If stored, the operation and effect of improving the quality of synthesized speech can be obtained even in such a case.

Further, in this embodiment, from all combinations of the diffusion patterns stored by the diffusion pattern storage / selection unit and all combinations of the pulse vector position candidates generated by the pulse vector generation unit 6, ) Is described in the case of specifying the combination number that maximizes the reference value in a closed loop, but the preliminary selection is performed based on the parameters (such as the ideal gain of the adaptive code vector) obtained before the identification of the random codebook number, Similar functions and effects can be obtained by searching in an open loop.

Further, by constituting a voice signal communication system or a voice signal recording system having the voice coding device / decoding device, the operation and effect of the sound source vector generation device described in the first embodiment can be obtained. be able to.

(Embodiment 3) FIG. 4 is a block diagram showing the configuration of a CELP speech coding apparatus according to the present embodiment.

FIG. 4 shows a CELP speech coding apparatus using the excitation vector generating apparatus (FIG. 1) according to the first embodiment as a random codebook, and the ideal adaptive code gain obtained before searching for the random codebook. Using the value to store the diffusion pattern
FIG. 4 is a diagram for explaining a method of performing preliminary selection of a diffusion pattern stored in a selection unit, and FIG.
This is the same as the described CELP speech coding apparatus. Therefore, the description of the present embodiment is limited to the description of the vector quantization process of the noise source information in the CELP speech coding apparatus shown in FIG.

In FIG. 4, reference numeral 407 denotes an adaptive codebook;
9 is an adaptive code gain weighting unit, and 408 is the first embodiment.
The noise codebook 410 constituted by the excitation vector generation apparatus described in (1), 410 is a noise code gain weighting unit, 405
Is a synthesis filter, 406 is a distortion calculation unit, 413 is a code number specifying unit, 415 is a spreading pattern storage / selection unit, 416 is a pulse vector generation unit, 417 is a pulse vector spreading unit, 418 is a spreading vector addition unit, and 419 is adaptive. It is a gain determination unit. However, in the present embodiment, at least one of the M types (M ≧ 2) of the diffusion patterns stored by the diffusion pattern storage / selection unit 415 is:
Learning is performed in advance so as to reduce the quantization distortion generated when the noise source information is vector-quantized, and the diffusion pattern is obtained as a result of the learning.

In this embodiment, for the sake of simplicity, the number N of channels of the pulse vector generation unit is 3, and the number M of types of spread pulses per channel stored in the spread pattern storage / selection unit is 2, Further, one of the M types (M = 2) of diffusion patterns is a diffusion pattern obtained by the learning, and the other is a random number vector sequence (hereinafter, referred to as a random pattern) generated by a random number vector generation device. The description will be made assuming that. By the way, the diffusion pattern obtained by the above learning is shown as w11 in FIG.
It has been found that the length is relatively short, resulting in a pulse-shaped diffusion pattern.

In the CELP speech coding apparatus shown in FIG. 4, an adaptive codebook number specifying process is performed before vector quantization of noise excitation information. Therefore, at the time of performing the vector quantization process of the noise excitation information, it is possible to refer to the vector number (adaptive code number) of the adaptive codebook and the ideal adaptive code gain (tentatively determined). In the present embodiment, the preliminary selection of the spreading pulse is performed using the ideal adaptive code gain value.

Specifically, first, immediately after the end of the adaptive codebook search, the ideal value of the adaptive code gain held in code number specifying section 413 is output to distortion calculating section 406. The distortion calculation section 406 outputs the adaptive code gain received from the code number identification section 413 to the adaptive gain determination section 419. The adaptive gain determination unit 419 firstly outputs the distortion calculation unit 406
The magnitude of the received ideal adaptive code gain is compared with a preset threshold. Next, the adaptive gain determination unit 41
9 is based on the result of the above-mentioned magnitude comparison and stores the diffusion pattern
A control signal for preliminary selection is sent to selection section 415. When the adaptive code gain is large in the magnitude comparison, the content of the control signal is selected from a diffusion pattern obtained by learning in advance so as to reduce the quantization distortion generated when the noise excitation information is vector-quantized. In the case where the adaptive code gain is not large in the magnitude comparison, it is instructed to preliminarily select a spreading pattern different from the spreading pattern obtained as a result of learning.

Then, in the diffusion pattern storage / selection unit 415, only the diffusion pattern on the side obtained by learning from the M (M = 2) diffusion patterns stored in each channel is preliminarily selected. Thus, the number of combinations of diffusion patterns can be greatly reduced. As a result, it is not necessary to calculate the distortion for all the combination numbers of the diffusion pattern, and the vector quantization of the noise source information can be efficiently performed with a small amount of calculation.

Further, the noise code vector has a pulse-like shape when the value of the adaptive gain is large (when the voicedness is strong), and when the adaptive gain value is small (when the voicedness is weak). ) Has a random shape. Therefore,
Since a noise code vector having an appropriate shape can be used for each of a voiced section and an unvoiced section of a voice signal, it is possible to improve the quality of a synthesized voice.

In the present embodiment, for simplicity of explanation, the number of channels N of the pulse vector generation unit is 3, and the number M of types of spread pulses per channel stored in the spread pattern storage / selection unit is 2, Although the description has been limited to the case, even when the number of channels in the pulse vector generation unit and the number of diffusion patterns per channel in the diffusion pattern storage / selection unit are different from the above description, the same effects and effects can be obtained.

In this embodiment, for simplification of description, of the M types (M = 2) of diffusion patterns stored for each channel, one type is the diffusion pattern obtained by the learning, and the other type is the diffusion pattern obtained by the learning. Although the case of a random pattern has been described, if at least one type of diffusion pattern obtained by learning is stored for each channel, the same effect can be obtained even in cases other than the above.・ An effect can be expected.

In this embodiment, the case where the magnitude information of the adaptive code gain is used as means for preliminary selection of the spreading pattern has been described. Further effects and effects can be expected when parameters representing the objective characteristics are used together.

Further, by constituting an audio signal communication system or an audio signal recording system having the above-mentioned audio encoding device, the operation and effect of the sound source vector generation device described in the first embodiment can be obtained.

(Embodiment 4) FIG. 5 is a block diagram showing the configuration of a CELP speech coding apparatus according to the present embodiment.

FIG. 5 shows a CELP speech coding apparatus using the excitation vector generation apparatus (FIG. 1) of the first embodiment as a noise codebook, using information available at the time of vector quantization of noise excitation information. The purpose of the present invention is to perform preliminary selection of a plurality of diffusion patterns stored in the diffusion pattern storage / selection unit by using a coding distortion (S / N ratio) generated when the number of an adaptive codebook is specified as a reference for preliminary selection. It is characterized by using the size of the expression. Note that the parts other than the noise codebook peripheral part in FIG. 5 are the same as the CELP speech coding apparatus shown in FIG. Therefore, the description of the present embodiment will be limited to the description of only the vector quantization process of the noise source information in the CELP speech coding apparatus shown in FIG.

In FIG. 5, reference numeral 507 denotes an adaptive codebook;
9 is an adaptive code gain weighting unit, and 508 is the first embodiment.
510 is a noise code gain weighting unit configured by the excitation vector generation apparatus described in
Is a synthesis filter, 506 is a distortion calculation unit, 513 is a code number identification unit, 515 is a diffusion pattern storage / selection unit, 516 is a pulse vector generation unit, 517 is a pulse vector diffusion unit, 518 is a diffusion vector addition unit, and 519 is distortion. It is a power determination unit. However, in the present embodiment, at least one of the M types (M ≧ 2) of the diffusion patterns stored by the diffusion pattern storage / selection unit 515 is:
It shall be a random pattern.

In the present embodiment, for simplicity of explanation, the number of channels N of the pulse vector generation unit is 3, and the number M of types of spreading pulses per channel stored in the spreading pattern storage / selection unit is 2, Further, one of the M types (M = 2) of diffusion patterns is learned in advance so that one type is a random pattern, and the other type is previously learned to reduce quantization distortion caused by vector quantization of noise source information. Is assumed to be the diffusion pattern obtained as a result.

In the CELP speech coding apparatus shown in FIG. 5, the number identification processing of the adaptive codebook is performed before the vector quantization processing of the noise excitation information. Therefore, at the time of performing the vector quantization process of the noise excitation number, the adaptive codebook vector number (adaptive code number), the ideal adaptive code gain (tentatively determined), and the target vector for adaptive codebook search are Can be referenced. In the present embodiment, preliminary selection of a spreading pulse is performed using coding distortion (expressed by an S / N ratio) of an adaptive codebook that can be calculated from the above three information.

Specifically, first, immediately after the end of the adaptive codebook search, the values of the adaptive code number and the adaptive code gain (ideal gain) held in the code number specifying section 513 are output to the distortion calculating section 506. The distortion calculation unit 506 uses the adaptive code number and the adaptive code gain received from the code number identification unit 513 and the target vector for adaptive codebook search to encode distortion (S / N) caused by identification of the adaptive codebook number. Ratio). The calculated S / N ratio is output to distortion power determination section 519.

First, the distortion power determination unit 519 compares the S / N ratio received from the distortion calculation unit 506 with a preset threshold value. Next, the distortion power determination unit 519
Sends a control signal for preliminary selection to the diffusion pattern storage / selection unit 515 based on the result of the magnitude comparison. When the S / N ratio is large in the magnitude comparison, the content of the control signal is a spread obtained as a result of learning in advance so as to reduce coding distortion caused by coding the target vector for noise codebook search. When the S / N ratio is small in the magnitude comparison, an instruction to select a diffusion pattern of a random pattern is issued.

Then, in diffusion pattern storage / selection section 515, only one of the M types (M = 2) of diffusion patterns stored in each channel is preliminarily selected, and the combination of the diffusion patterns is greatly increased. Can be reduced. As a result, it is not necessary to calculate distortion for all the combination numbers of the diffusion pattern, and the noise code number can be efficiently specified with a small amount of calculation. Further, the noise code vector has a pulse shape when the S / N ratio is large, and has a random shape when the S / N ratio is small. Therefore, the shape of the noise code vector can be changed in accordance with the short-time characteristics of the speech signal, so that the quality of the synthesized speech (particularly, a noise section) can be improved.

In this embodiment, for simplicity of explanation, the number of channels N of the pulse vector generation unit is 3, and the number M of types of spreading pulses per channel stored in the spreading pattern storage / selection unit is 2. Although the description has been limited to the case, the same effects and effects can be obtained even when the number of channels of the pulse vector generation unit and the number of types of diffusion patterns per channel are different from those described above.

Further, in this embodiment, for simplification of description, M types (M =
Of the diffusion patterns of 2), one type is a diffusion pattern obtained by the above learning, and another type is a random pattern. However, at least one type of random pattern is provided for each channel. If it is stored, the same effect and
Action can be expected.

In the present embodiment, only the magnitude information of the coding distortion (expressed in S / N ratio) caused by the specification of the adaptive code number is used as means for preliminary selection of the spreading pattern. When the information that can express the short-time characteristics of the audio signal more accurately is used together, further effects and effects can be expected.

Further, by configuring an audio signal communication system or an audio signal recording system having the audio encoding device, the operation and effect of the sound source vector generation device described in the first embodiment can be obtained.

[0086]

As described above, according to the present invention, the shape (characteristics) of the diffusion pattern obtained by analyzing actual sound source information or learning based on the information can be reflected in the pulse vector. Since it is possible to generate an excitation vector having a shape (characteristic) having a high similarity to an actual excitation vector and use it as a noise code vector, the quality is higher than when a conventional algebraic excitation generator is used for a noise codebook. And a synthesized voice with high

[Brief description of the drawings]

FIG. 1 is a configuration block diagram of a sound source vector generation device according to an embodiment of the present invention;

FIG. 2 is a configuration block diagram of a speech encoding device according to an embodiment of the present invention;

FIG. 3 is a configuration block diagram of a speech decoding device according to an embodiment of the present invention;

FIG. 4 is a configuration block diagram of a speech encoding device according to an embodiment of the present invention;

FIG. 5 is a configuration block diagram of a speech encoding device according to an embodiment of the present invention;

FIG. 6 is a configuration block diagram of a conventional CELP-type speech coding apparatus.

FIG. 7 is a block diagram showing the configuration of a conventional CELP-type speech decoding device.

[Explanation of symbols]

101, 216, 416, 516 Pulse vector generator 102, 215, 415, 515 Spread pattern storage / selector 103, 217, 417, 517 Pulse vector spreader 104, 218, 418, 518 Spread vector adder 105 Sound source vector 201 , 401, 501 Input speech 202, 402, 502 Linear prediction analysis unit 203, 403, 503 Linear prediction coefficient coding unit 204, 302, 404, 504 Linear prediction coefficient decoding unit 205, 309, 405, 505 Synthesis filter 206, 406, 506 distortion calculators 207, 303, 407, 507 adaptive codebooks 208, 304, 408, 508 noise codebooks 209, 306, 409, 509 adaptive code gain weighters 210, 307, 410, 510 noise code gain weighters 211, 05, 411, 511 Weighted codebook 212, 308, 412, 512 Adder 213, 413, 513 Code number specifying unit 214, 414, 514 Code output unit 301 Code input unit 310 Synthesized voice 419 Adaptive gain determination unit 519 Distortion power determination Department

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-280200 (JP, A) JP-A-2-282800 (JP, A) JP-A-6-130994 (JP, A) JP-A-6-130994 195098 (JP, A) JP-A-10-63300 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G10L 19/00-19/14 H03M 7/30 H04B 14/04

Claims (5)

(57) [Claims] A linear predictor for linear predictive analysis of an input speech signal.
Measurement and analysis means and a random codebook for generating a random code vector
And the synthesized speech vector
CELP speech code having synthesis filter for generating
A noise generator, wherein the noise codebook includes a pulse vector generator that supplies a pulse vector from an algebraic codebook having a plurality of channels, a spreading pattern storage that stores a plurality of spreading patterns, and A selection unit for selecting any one of the plurality of diffusion patterns; and a supplied pulse vector and the selected diffusion pattern.
Is convolved with each channel for each channel as a diffusion vector
A CELP-type speech coding apparatus, comprising: a spreading vector generating apparatus having a pulse vector spreading section for outputting . 2. The method according to claim 1, wherein the random codebook is a spread vector generator.
Add the diffusion vectors of multiple channels output from the
A sound source vector generator that outputs as a source vector
The CELP-type speech code according to claim 1, wherein
Encryption device . 3. Convolution in a pulse vector spreading unit
Is a linear convolution, or
3. A CELP-type speech coding apparatus according to claim 2. 4. A step of performing linear predictive analysis on an input speech signal.
Generating a random code vector; and the random code
Generating a synthesized speech vector by inputting the vector;
A CELP-type speech coding method having the following: wherein the noise code vector is a pulse vector from an algebraic codebook having a plurality of channels.
And a diffusion pattern storage unit that stores multiple diffusion patterns.
Selectively reading the diffusion pattern; and supplying the pulse vector and the read diffusion pattern.
Pattern is convolved for each channel and
CELP type speech coding method is generated by excitation vector generation method, and a step of and outputs, a. 5. A process for outputting as a diffusion vector.
The convolution is a linear convolution.
The CELP-type speech encoding method according to claim 4 .