JP2002169595A - Fixed sound source code book and speech encoding/ decoding apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To deal with a low bit rate while assuring the number of pieces of sound source pulses. SOLUTION: The fixed sound source code book 207 includes a first sound source code book 401 which is relatively high in time resolution to partially express sound source vectors and a second sound source code book 402 which is relatively low in time resolution to express the entire part of the sound source vectors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low bit rate speech coding apparatus in a mobile communication system for coding and transmitting a speech signal, and more particularly to a CELP (Code Excited Linear Predictio) using a pulsed sound source as a driving sound source signal.
The present invention relates to an n) type speech coding device.

[0002]

2. Description of the Related Art In the field of digital mobile communication, packet communication typified by the Internet communication, and voice storage, voice information is compressed for effective use of transmission line capacity such as radio waves and storage media. A speech encoding device for encoding with efficiency is used. Above all CE
A system based on the LP system has been widely put into practical use at medium and low bit rates. For information on CELP technology, see MRSchroeder and bsAtal: "Code-ExcitedLinear
Prediction (CELP): High-quality Speech at VeryLow B
it Rates ", Proc. ICASSP-85, 25.1.1, pp.937-940, 19
85 ".

[0003] In the CELP type speech coding system, a digitized speech signal is divided into a fixed frame length (about 5 ms to 50 ms), a speech is linearly predicted for each frame, and a prediction residual by the linear prediction for each frame. (Excitation signal) is encoded using an adaptive codebook having a known waveform and a noise (fixed) codebook.

[0004] The adaptive codebook stores driving excitation signals generated in the past, and is used to represent a periodic component of an audio signal. The fixed codebook stores a predetermined number of vectors having a predetermined shape prepared in advance, and is used for mainly expressing aperiodic components that cannot be expressed by the adaptive codebook. As a vector stored in the fixed codebook, a vector composed of a random noise sequence, a vector expressed by a combination of several pulses, and the like are used.

[0005] An algebraic fixed codebook is one of the typical fixed codebooks that express the above-mentioned vector by a combination of several pulses. Specific contents of the algebraic fixed codebook are shown in "ITU-T Recommendation G.729" and the like.

A conventional algebraic fixed codebook will be specifically described with reference to FIG. FIG. 14 is a diagram illustrating a manner in which a fixed excitation vector is generated from an algebraic fixed codebook. In FIG. 14, three unit pulses (having an amplitude value of 1) are generated from different tracks, and after being given appropriate polarities by the polarity applying units 1401 to 1403, the adding unit 1404
, The three pulses are added to generate a fixed sound source vector.

Each track is different in the position where the pulse can be arranged. In FIG. 14, the first track is # 0,3,
6,9,12,15,18,21｝
The truck is located in one of the eight locations {1,4,7,10,13,16,19,22}, and the third is {2,5,8,11,14,17,20,23}
One of the eight units
The book can be set up one by one. In this example, since each pulse has eight positions and two positive and negative polarities, three bits of position information and one bit of polarity information are used to represent each sound source pulse. Therefore, it becomes a fixed excitation codebook of 12 bits in total.

[0008]

However, when the above-mentioned conventional algebraic fixed codebook is applied to a speech coding apparatus for a low bit rate such as 4 kbit / s or less,
Due to the lack of bits, the number of positions that are not included in any track (points where no pulse is formed) increases, or the polarity information cannot be assigned to each pulse, and the coded voice quality rapidly deteriorates. There is a problem. In particular, in order to apply to a rate of 4 kbit / s or less, it is necessary to reduce the number of sound source pulses in addition to the reduction of the number of position candidates in each track.

[0009] The smaller the number of excitation pulses, the greater the quality degradation due to the reduction in the number of pulses. Therefore, it is necessary to ensure that the number of excitation pulses is as large as possible and to cover a large number of position candidates with each track. This is an important issue in improving the performance of the low bit rate CELP type speech coding apparatus used.

The present invention has been made in view of the above points, and provides a fixed excitation codebook and a speech encoding / decoding apparatus capable of coping with a low bit rate while securing the number of excitation pulses. The purpose is to:

[0011]

SUMMARY OF THE INVENTION A fixed excitation codebook according to the present invention comprises a first excitation codebook which partially expresses an excitation vector and has a relatively high time resolution, and a relatively time resolution which expresses the entire excitation vector. And a second excitation codebook having a low power consumption.

According to this configuration, the number of required bits can be reduced by using a codebook with a high time resolution which requires a large number of bits. In addition, since an acoustically important part is often concentrated on a part of the excitation vector, high quality can be realized even in such an excitation codebook having a partially high temporal resolution. In addition, since an excitation codebook that covers the whole is also provided, it is possible to cope to some extent even when aurally important parts are scattered throughout the vector.

A fixed excitation codebook according to the present invention is a fixed excitation codebook used for an excitation vector generation device for generating an excitation vector composed of several pulses, and each excitation codebook is provided within a limited range with respect to the entire excitation vector. A first excitation codebook storing excitation vectors in which pulses are finely arranged;
A second excitation codebook storing excitation vectors obtained by coarsely arranging each pulse over a wide range of the entire excitation vector;
Is adopted.

According to this configuration, even with a small number of bits, it is possible to increase the number of excitation pulses and the positions where the excitation pulses can be arranged.

The fixed excitation codebook of the present invention is an excitation codebook in which one pulse is arranged in one of two adjacent samples, and different polarities are assigned to both samples. Take the configuration.

According to this configuration, 1 is set for two positions.
Since the bit polarity information is assigned, the number of necessary bits can be halved compared to the conventional case where one bit polarity is assigned to one position. Further, since the two positions are adjacent to each other, it is possible to suppress deterioration caused by handling the two positions collectively.

The fixed excitation codebook of the present invention is an excitation codebook in which a plurality of pulses are arranged algebraically,
The present pulse adopts a configuration in which an excitation codebook that generates only combinations that are arranged close to each other is provided as the first excitation codebook, and the excitation codebook is provided as the second excitation codebook. .

According to this configuration, it is possible to realize an algebraic fixed excitation codebook that can secure a large number of excitation pulses and a large possible position of each pulse with a small number of bits.

The fixed excitation codebook of the present invention comprises a first excitation codebook and a second excitation codebook, and a third excitation codebook for generating an excitation vector like white noise. take.

According to this configuration, it is possible to satisfactorily express a noisy signal (such as a fricative consonant) which is difficult to express with an algebraic fixed excitation codebook having a small number of excitation pulses.

The fixed excitation codebook of the present invention is a fixed excitation codebook used for an excitation vector generation apparatus having a pulse excitation codebook and a noise excitation codebook, wherein the generated excitation vector is a pulse excitation codebook. Or the noise excitation codebook, and when encoding the input signal using the generated excitation vector, the excitation vector generated from the noise excitation codebook increases as the coding distortion increases. A configuration is adopted in which weighting is performed so as to facilitate selection.

According to this configuration, by applying a noise sound source instead of a pulse sound source to an input signal that cannot be expressed well, it is possible to obtain an acoustically natural encoding distortion. Become.

The fixed excitation codebook of the present invention has a configuration in which the first and second excitation codebooks are provided as pulse excitation codebooks and the third excitation codebook is provided as a noise excitation codebook.

According to this configuration, it is possible to greatly improve the performance of the fixed excitation codebook for a noisy signal.

According to the fixed sound source vector generation method of the present invention, a first sound source generation for generating a pulse sound source in which positions where each pulse can be taken is set finely and at least two pulses are restricted so as to approach each other. The second step is to generate a pulse sound source in which the steps and possible positions of each pulse are roughly set, and no limitation is imposed on the combination of each pulse.
, A third excitation generation step for generating an excitation composed of random noise signals, and weighting such that the excitation vector generated in the third excitation generation step is more easily selected as the coding distortion increases. Performing a weighting step.

According to this method, the number of excitation pulses and the positions where the excitation pulses can be arranged can be increased with a small number of bits, and the subjective quality can be improved even for noise-like signals. .

The storage medium according to the present invention is a computer-readable recording medium storing a sound source generation program, wherein the sound source generation program has at least two positions where each pulse can be taken. A first sound source generation procedure for generating a pulse sound source that is restricted so that the pulses approach each other, and a pulse sound source in which the possible positions of each pulse are roughly set and no limitation is applied to the combination of each pulse , A third excitation generation procedure for generating an excitation composed of random noise signals, and an excitation vector generated in the third excitation generation procedure is selected as the coding distortion increases. And a weighting procedure for performing weighting so as to make it easier.

According to this configuration, any one of the above-described functions and effects can be obtained in the storage medium.

The speech coding apparatus of the present invention comprises the above fixed excitation codebook, an adaptive excitation codebook representing a periodic component of the input speech signal, and means for quantizing and encoding parameters representing the spectral characteristics of the input speech signal. Means for synthesizing a synthesized speech signal using the excitation vector and the parameter generated from the fixed excitation codebook and the adaptive excitation codebook,
Means for determining an output from the fixed codebook and the adaptive codebook such that distortion between the input speech signal and the synthesized speech signal is reduced.

According to this configuration, any one of the above-described functions and effects can be obtained by the fixed excitation codebook, so that high-quality speech coding at a low bit rate can be realized.

The speech decoding apparatus of the present invention decodes the fixed excitation codebook, the adaptive excitation codebook representing the periodic component of the synthesized speech signal, and the parameters representing the spectral characteristics encoded by the speech encoding apparatus. Means for decoding the excitation vector determined in the speech encoding apparatus from the fixed excitation codebook and the adaptive excitation codebook, and synthesizing a synthesized speech signal from the decoded excitation vector and the parameter. The configuration provided is adopted.

According to this configuration, any one of the above-described functions and effects can be obtained with the fixed excitation codebook, so that a high-quality speech signal can be decoded at a low bit rate.

[0033] A speech signal transmitting apparatus according to the present invention includes the speech coding apparatus having the above-described configuration. Further, an audio signal receiving apparatus according to the present invention includes the audio decoding apparatus having the above configuration.

[0034] A base station apparatus according to the present invention includes the voice signal transmitting apparatus and / or the voice signal receiving apparatus having the above-described configuration. Further, a mobile station device according to the present invention includes the voice signal transmitting device and / or the voice signal receiving device configured as described above.

With these configurations, it is possible to improve the performance of the digital radio communication system even at a low bit rate.

[0036]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram illustrating a configuration of a transmission device and a reception device including a speech encoding / decoding device according to an embodiment of the present invention.

In FIG. 1, an audio signal is converted into an electric signal by an input device 101 of a transmitting device, for example, a microphone, and is output to an A / D converter 102. The A / D converter 102 converts an (analog) signal output from the input device 101 into a digital signal, and outputs the digital signal to the speech encoder 103.

Speech coding apparatus 103 encodes the digital signal output from A / D conversion apparatus 102 by using a speech coding method described later, and outputs the obtained speech coded information to RF modulation apparatus 104. I do.

The RF modulation device 104 is a voice coding device 1
The audio coded information output from the receiver 03 is converted into a signal to be transmitted on a propagation medium such as a radio wave, and the signal is output to the transmitting antenna 105. The transmitting antenna 105
The output signal output from the RF modulator 104 is converted into a radio wave (R
F signal).

The RF signal is transmitted to the receiving antenna 10 of the receiving apparatus.
6 and output to the RF demodulator 107. RF demodulation device 107 demodulates audio encoded information from the RF signal output from receiving antenna 106 and outputs the audio encoded information to audio decoding device 108.

The audio decoding device 108 is an RF demodulator 1
The audio signal is decoded using the audio decoding method described later from the audio coded information output from 07, and the decoded audio signal is output to the D / A converter 109. The D / A converter 109 converts the digital audio signal output from the audio decoder 108 into an analog electric signal, and outputs the electric signal to an output device 110, for example, a microphone. The output device 110 converts the electric signal into vibration of air and outputs the sound as sound waves so as to be audible to human ears.

By providing at least one of the voice signal transmitting device and the receiving device having the above configuration, a base station device and a mobile terminal device in a mobile communication system can be configured.

Speech encoding apparatus 103 in the speech signal transmitting apparatus has the configuration shown in FIG. FIG. 2 is a block diagram showing a configuration of the speech coding apparatus according to the embodiment of the present invention.

In FIG. 2, the input audio signal is represented by A in FIG.
The signal is output from the / D conversion device 102 and is input to the preprocessing unit 200. The pre-processing unit 200 performs a high-pass filter process for removing a DC component (a DC component), a waveform shaping process that leads to an improvement in the performance of a subsequent encoding process, and / or a pre-emphasis process, and processes the signal (Xin). Is output to the LPC analysis unit 201, the adder 204, and the parameter determination unit 212.

LPC analysis section 201 performs a linear prediction analysis using Xin, and outputs an analysis result (linear prediction coefficient) to LPC quantization section 202. LPC quantization section 202 calculates LPC
The linear prediction coefficient (LP) output from the PC analysis unit 201
C), and outputs the quantized LPC to the synthesis filter 203 and the code L representing the quantized LPC to the multiplexing unit 213.

The synthesis filter 203 is the same as the quantization LPC
Is subjected to filter synthesis using the filter coefficients and the driving sound source output from the adder 210, and the synthesized signal is added to the adder 20.
Output to 4. The adder 204 calculates an error signal between the Xin and the synthesized signal, and outputs the error signal to the auditory weighting unit 211.

The auditory weighting section 211 performs auditory weighting on the error signal output from the adder 204, calculates the distortion between the Xin and the synthesized signal in an auditory weighting area, and obtains a parameter determining section 212. Output to

The parameter deciding section 212 controls the adaptive excitation codebook 205, the fixed excitation codebook 207, and the fixed excitation codebook 207 so that the coding distortion output from the auditory weighting section 211 is minimized.
And a signal to be generated from the quantization gain generation unit 206.

It is to be noted that not only the coding distortion output from the auditory weighting unit 211 is minimized, but also a signal to be generated from the three processing units is determined by using another coding distortion using the Xin. By doing so, the coding performance can be further improved.

The adaptive excitation codebook 205 has been
The sound source signal output by the buffer 10 is buffered, and an adaptive sound source vector is cut out from the position specified by the signal (A) output from the parameter determination unit 212 and output to the multiplier 208.

[0051] Fixed excitation codebook 207 outputs to multiplier 209 a vector having a shape specified by signal (F) output from parameter determination section 212. Quantization gain generating section 206 multiplies adaptive excitation gain and fixed excitation gain specified by signal (G) output from parameter determining section 212 by multipliers 208 and 209, respectively.
Output to

The multiplier 208 includes a quantization gain generation unit 206
Are multiplied by the adaptive excitation vector output from adaptive excitation codebook 205 and output to adder 210. Multiplier 209 multiplies the fixed excitation vector output from fixed excitation codebook 207 by the quantized fixed excitation gain output from quantization gain generating section 206, and outputs the result to adder 210.

Adder 210 receives the adaptive excitation vector and the fixed excitation vector after gain multiplication from multipliers 208 and 209, respectively, adds the vectors, and outputs the result to synthesis filter 203 and adaptive excitation codebook 205. .

Finally, the multiplexing unit 213 receives the code L representing the quantized LPC from the LPC quantization unit 202, the code A representing the adaptive excitation vector, the code F representing the fixed excitation vector, And a code G representing a quantization gain, the information is multiplexed and output to the transmission path as coded information.

The above speech coding apparatus has a specific configuration of fixed excitation codebook 207 and features of parameter determination section 212. 3 and 4 are block diagrams showing a configuration of fixed excitation codebook 207, and FIG. 5 is a block diagram showing a configuration of parameter determining section 212.

In FIG. 3, first excitation codebook 301
Is an excitation codebook that generates an excitation vector in which excitation pulses are arranged within a limited range with fine precision, and a second excitation codebook 302 generates an excitation vector in which excitation pulses are arranged with coarse accuracy over a wide range. A sound source codebook to be generated,
The changeover switch 303 is a switch for selecting one of an excitation vector generated from the first excitation codebook 301 and an excitation vector generated from the second excitation codebook 302.

In the fixed excitation codebook, a fixed excitation vector specified by signal (F) input from parameter determining section 212 in FIG. 2 is converted by first excitation codebook 301 or second excitation codebook 302. Generate and changeover switch 3
The signal is output as a fixed sound source vector via the signal line 03.

In FIG. 4, first excitation codebook 401 and second excitation codebook 402 correspond to first excitation codebook 301 and second excitation codebook 302 in FIG. 3, respectively, and have the same configuration. belongs to. The difference between the fixed excitation codebook shown in FIG. 4 and the fixed excitation codebook shown in FIG. 3 is that a third excitation codebook 403 is provided. In FIG. 4, reference numeral 404 denotes a changeover switch.

First and second excitation codebooks 401 and 402
Generates a fixed excitation vector composed of a small number (about 2 to 4) of excitation pulses, whereas the third excitation codebook 403 generates a fixed excitation vector composed of a large number of excitation pulses and a random number sequence.

The most basic and general one is to store a predetermined type of white Gaussian noise vector, select an appropriate one from the stored white Gaussian noise vectors, and output it as a fixed sound source vector. In addition, it is also common to arrange a large number (at least about 10 or more) of excitation pulses at random with random polarity. By providing such a third excitation codebook, it is possible to represent a noise-like signal that cannot be represented by a small number of pulse excitations.

FIGS. 7, 8 and 9 show examples in which the first excitation codebook and the second excitation codebook in FIGS. 3 and 4 are configured using algebraic fixed codebooks. FIG.
It is a figure which shows the example of the 1st excitation codebook (301,401) which produces | generates a fixed excitation vector from the pulse of three tracks (three), and shows the position and polarity of the pulse which can be set in each track. ing. The numbers in the figure indicate the positions of the pulses.

The feature of this algebraic fixed excitation codebook is that each track is composed of pulse position candidate points of two adjacent samples, and pulses of positive and negative polarities are separately assigned to the two adjacent samples. It is being done. 2
There are a total of four ways to raise one pulse for a sample point.
This is a combination of the two methods having the lowest similarity in the sense that the pulse position and the pulse polarity are different from each other.

Therefore, when the above four ways are reduced to two ways, it can be said that the method of assigning different polarities to two adjacent samples as described above has the least redundancy. Also, since two samples are adjacent,
If a pulse of the required polarity cannot be set at one sample point (due to the position and polarity restrictions described above), the required polarity (although the position is shifted by one sample) at the other sample point , And the probability that such a pulse can be substituted for the pulse originally required increases.

When the number of bits representing the pulse position is insufficient, not all the pulse position candidate points in the track need to be two adjacent samples. The track configuration may be such that the distance of the sample is two or more samples (one or more sample points exist between the candidate points). However, in such non-adjacent portions, the above-described effect of causing one pulse to substitute a necessary pulse at the other position cannot be expected.

A pulse is generated one by one from the three tracks configured as described above, and becomes a vector composed of three pulses. The last generated vector multiplied by the polarity is the output vector from the excitation codebook. Here, an example in which three sound source pulses are used has been described, but the above concept can be applied to any number of sound source pulses. Further, the effectiveness can be obtained even in a configuration in which the polarity of the entire vector to be multiplied last is omitted.

FIG. 8 shows a second excitation codebook (30) for generating a fixed excitation vector from three track (three) pulses.
2, 402). The configuration of the track (pulse position and polarity) is the same as that of a general algebraic fixed codebook. The difference is that the combination of three pulses is limited.

FIG. 8 shows an example in which only combinations that are close to all three are generated. The dashed line shown in each track in the figure is a candidate for a pulse position. For example, when a pulse whose sample point is 3 is selected in the first track (shown by a solid line in the figure), the second track is shown. The pulse position of the track is limited to 4 or 7, and the pulse position of the third track is limited to 5 or 8, and a sound source vector can be generated only by a combination of these position candidates. That is, the sound source vector is generated using only two position candidates immediately after the leading pulse. Here, the position candidate is 2
However, the number of position candidates may be three or four depending on the number of bits.

FIG. 9 also shows a second excitation codebook (30) for generating a fixed excitation vector from three track (three) pulses.
2, 402). The difference between the excitation codebook shown in FIG. 9 and the excitation codebook shown in FIG. 8 is that the method of limiting the combination of three pulses is different.

In FIG. 9, when the first pulse position is 3, the second pulse position is limited to 4, and the third pulse position is limited to 11. That is, 1 for the first pulse
Only the vector of the combination of a book at one place immediately after it and another book at one place slightly away is generated.

Since it is assumed that this excitation codebook is used in combination with the excitation codebook shown in FIG. 8, the position of the pulse set at the last distant location is as shown in FIG.
Of the excitation codebook (a range distant from the range limited by the configuration of FIG. 8 (if the range exceeds the vector length, it may be circulated to the beginning of the frame)).

The number of pulse positions to be limited is not limited to one as described above, but may be two or three in accordance with the number of available bits. The number of third pulse position candidates distant from the pulse may be different.

FIG. 5 is a block diagram showing a configuration of parameter determining section 212 in the speech coding apparatus shown in FIG. In FIG. 5, first, the adaptive excitation vector selection unit 50
1 finds an adaptive excitation vector that minimizes the output from the auditory weighting unit 211 in FIG. 2 from the adaptive excitation codebook 205, and outputs a code A corresponding to this adaptive excitation vector. At this stage, nothing is output from the fixed excitation codebook, and synthesis filter 203 is driven only by the adaptive excitation codebook. Further, as the gain multiplied by the adaptive excitation vector, an ideal gain obtained by calculation is used.

Next, after the adaptive excitation vector is fixed to the adaptive excitation vector selected by the adaptive excitation vector selection section 501, the fixed excitation vector selection section 502 outputs the output (weighted error) from the auditory weighting section 211. ) Is fixed to the fixed excitation codebook 20.
7, and outputs a code F corresponding to the fixed excitation vector. At this stage, an ideal gain obtained by calculation is used as a gain for multiplying the already selected adaptive excitation vector and the newly selected fixed excitation vector. Further, the fixed excitation vector may be selected not only by minimizing the weighted error but also by using the input signal Xin after the preprocessing.

Next, the adaptive excitation vector and the fixed excitation vector are fixed to those selected as described above, and then the quantization of the gain multiplied by both vectors is performed. The excitation gain quantization unit 503 quantizes the quantized excitation gain so as to minimize the weighted error, and outputs a code G corresponding to the quantized excitation gain.

The parameter deciding section shown in FIG. 5 has the feature of fixed sound source vector selecting section 502. FIG. 6 is a block diagram illustrating a configuration of the fixed sound source vector selection unit 502. In FIG. 6, a first fixed sound source vector selecting unit 6
01 selects the first fixed excitation vector that minimizes the weighted error from the first excitation codebook 401,
Output to 4. Second fixed sound source vector selection unit 602
Selects the second fixed excitation vector that minimizes the weighted error from the second excitation codebook 402,
Output to 4.

The selecting unit 604 compares the weighted error between the first fixed sound source vector and the second fixed sound source vector, selects the fixed sound source vector with the smaller weighted error, and repeats this. The result is output to the attachment selector 605.

The third fixed sound source vector selection unit 603
A third fixed excitation vector that minimizes the weighted error is selected from third excitation codebook 403, and is output to weighted selection section 605.

The weighted selection section 605 generates a WSNR when a speech signal is synthesized using each of the first or second fixed excitation vector output from the selection section 604 and the third fixed excitation vector. (Input signal Xin after preprocessing
Is calculated as S, and a weighted error is set as N). One of the two fixed excitation vectors is selected according to the value of the WSNR, and a code F corresponding to the fixed excitation vector is output. A specific selection operation of the weighted selection unit 605 will be described later.

FIG. 10 is a view for explaining selection criteria of the weighted selection section 605. 10, the horizontal axis represents the WSNR of the audio signal synthesized using the third fixed sound source vector selected by the third fixed sound source vector selection unit 603.
The vertical axis indicates the WSNR value [dB] of the audio signal synthesized using the first or second fixed excitation vector selected by the selection unit 604, and the SN
They are shown as Rn and SNRp.

When selecting the optimal fixed sound source vector based on only the weighted distance, the straight line SNRn = S in FIG.
This is equivalent to making a selection depending on whether it is above or below NRp. That is, the straight line SNRp = SNR in FIG.
In the region below n, the WSNR becomes higher when the third fixed sound source vector is used. Therefore, the third fixed sound source vector is selected as the final fixed sound source vector, and the upper side of the straight line SNRp = SNRn In the region, the WSNR becomes higher when the first or second fixed excitation vector is used, so that the first or second fixed excitation vector is selected as the final fixed excitation vector.

However, when the absolute value of the WSNR is low regardless of which of the above two types of fixed sound source vectors is used, the ideal fixed sound source vector often looks like white noise. On the other hand, when such a white noise-like signal is encoded by a pulse excitation (first or second fixed excitation codebook), compared to the case of encoding by a noise-like excitation (third fixed excitation codebook). Although the SN ratio tends to be slightly higher, it is known that noise becomes subjectively jerky and causes quality deterioration.

Thus, in such a low SN ratio region,
In order to make it easier for the third fixed sound source vector to be selected as the final fixed sound source vector, in addition to the straight line SNRp = SNRn, the straight line SNRp = ((A−
B) / A) * SNRn + B is prepared and low SN (WSN)
Sometimes, the latter straight line is used as a determination boundary.
However, the rising portion of the voice often has a low SN ratio, and it is not desirable to use the latter straight line as the determination boundary even in such a rising portion.
Therefore, in order to adapt to such a case, it is desirable to provide a means for separately determining whether or not the section is a voiced section, and to operate the above-described weighted selection processing when it is determined that the section is not a voiced section.

Although the present embodiment has been described with respect to a configuration using the excitation codebook shown in FIGS. 7 to 9 and a noise excitation codebook such as Gaussian noise in combination, any one of the excitation codebooks is used. A configuration using only one type of excitation codebook is possible, and a configuration using two or more types of excitation codebooks in combination is also possible.

FIG. 11 is a flowchart showing a processing procedure of the fixed excitation codebook search, and FIG. 12 is a flowchart showing a processing procedure of the weighted selection.

In FIG. 11, first, a step (hereinafter, referred to as a step)
At 1101, a first excitation codebook search is performed, and a first excitation vector is selected. Next, ST1
At 102, a second excitation codebook search is performed.
Are selected. At this point, one of the first and second (the one with a smaller weighted error) is selected as a pulse excitation vector candidate.

Next, in ST1103, a third excitation codebook search is performed, and a third excitation code vector (noise excitation vector candidate) is selected. Finally, ST1104
In, weighted selection is performed, and an appropriate one of the pulse excitation vector candidate and the noise excitation vector candidate is selected as a fixed excitation vector.

In FIG. 12, in ST 1201,
WSNR (= S
NRp) is calculated by the following equation (1). In the calculation, it is not necessary to strictly follow equation (1).
An equivalent to the equation (1) or an equation obtained by removing the constant term in the equation (1) may be used.

SNRp = 10 * log10 (SSin / NNin) Equation (1) where SSin = Σ (Xin) * (Xin), NNin = Σ
(Xin-Sout) * (Xin-Sout) Here, Xin indicates an input signal after preprocessing, Sout indicates a synthesis filter output signal, and Σ indicates the sum of the number of samples of the vector length.

Next, in ST1202, the WSNR (= SNRn) when the noise source vector candidate is used is S
It is determined in the same manner as NRp. Next, in ST1203, it is checked whether SNRn> A, SNRp> A, or whether it is a voiced section. Selected as a fixed fixed sound source vector. Otherwise, the mobile terminal proceeds to ST1204.

In ST1204, SNRp> SNRn *
It is determined whether (AB) / A + B is satisfied, and if so, a pulse excitation vector candidate is selected as a final fixed excitation vector. If not, a candidate noise source vector is selected as the final fixed source vector.

FIG. 13 is a block diagram showing the speech decoding apparatus 108 shown in FIG.
FIG. 3 is a block diagram showing the configuration of FIG. In FIG. 13, RF
In the coded information output from the demodulation device 107, the coded information multiplexed by the demultiplexing unit 1301 is separated into individual code information. LPC code L separated
Is output to an LPC decoding section 1302, the separated adaptive excitation vector code A is output to an adaptive excitation codebook 1305, and the separated excitation gain code G is output to the quantization gain generation section 1
306 and the separated fixed excitation vector code F
Are output to fixed excitation codebook 1307.

The LPC decoding section 1302 decodes the LPC from the code L output from the demultiplexing section 1301 and outputs this to the synthesis filter 1303. Adaptive excitation codebook 1305 extracts an adaptive excitation vector from the position specified by code A output from demultiplexing section 1301, and outputs the vector to multiplier 1308.

Fixed excitation codebook 1307 generates a fixed excitation vector specified by code F output from multiplexing / demultiplexing section 1301, and outputs the generated fixed excitation vector to multiplier 1309. The quantization gain generation section 1306 decodes the adaptive excitation vector gain and the fixed excitation vector gain specified by the excitation gain code G output from the demultiplexing section 1301, and multiplies these by the multiplier 1
308 and 1309, respectively.

The multiplier 1308 multiplies the adaptive code vector by the adaptive code vector gain, and
Output to 0. A multiplier 1309 multiplies the fixed code vector by the fixed code vector gain, and
Output to 10 The adder 1310 includes an adder 1308,
The adaptive excitation vector after gain multiplication output from 1309 and the fixed excitation vector are added, and the synthesis filter 130
Output to 3.

The synthesis filter 1303 includes an adder 1310
The sound source vector output from the
Filter synthesis is performed using the filter coefficients decoded by the decoding unit 1302, and the synthesized signal is processed by the post-processing unit 1.
Output to 304.

The post-processing unit 1304 performs processing for improving the subjective quality of speech, such as formant emphasis and pitch emphasis, and processing for improving the subjective quality of stationary noise. Output as audio signal.

[0097] Further, the speech encoding / decoding device can be applied to a communication terminal device such as a base station device or a mobile station in a digital radio communication system. As a result, in a digital wireless communication system, high performance can be achieved even at a low bit rate.

The present invention is not limited to the above embodiment, but can be implemented with various modifications. For example, although the generation of the excitation vector according to the above embodiment has been described as a speech encoding device / speech decoding device, the generation of these excitation vectors may be configured as software.
For example, a program for generating the sound source vector is stored in a ROM
, And may be configured to operate according to an instruction of the CPU according to the program. Alternatively, the sound source vector generation program may be stored in a computer-readable storage medium, and the sound source vector generation program in the storage medium may be recorded in the RAM of the computer and operated according to the sound source vector generation program. In such a case, the same operation and effect as those of the above-described embodiment are exhibited.

[0099]

As described above, according to the present invention,
It is possible to provide a fixed excitation codebook in which good coding performance can be obtained with a small number of bits. This makes it possible to cope with a low bit rate while securing the number of sound source pulses.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a transmitting device and a receiving device provided with a speech encoding / decoding device according to an embodiment of the present invention.

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

FIG. 3 is a block diagram showing a fixed excitation codebook according to the embodiment of the present invention.

FIG. 4 is a block diagram showing a fixed excitation codebook according to the embodiment of the present invention.

FIG. 5 is a block diagram showing a parameter determining unit in the speech coding apparatus according to the embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration of a fixed sound source vector selecting unit of the sound source parameter determining unit shown in FIG.

FIG. 7 is a diagram showing a first excitation codebook of the fixed excitation codebook according to the embodiment of the present invention.

FIG. 8 is a diagram showing a second excitation codebook of the fixed excitation codebook according to the embodiment of the present invention.

FIG. 9 is a diagram showing a second excitation codebook of the fixed excitation codebook according to the embodiment of the present invention.

FIG. 10 is a view for explaining selection criteria of a weighted selection unit of a fixed excitation vector selection unit in the excitation parameter determination unit shown in FIG. 5;

FIG. 11 is a flowchart showing a fixed excitation codebook search processing procedure according to an embodiment of the present invention.

FIG. 12 is a flowchart showing a weighted selection processing procedure in a weighted selection unit in FIG. 10;

FIG. 13 is a block diagram showing a configuration of a speech decoding device according to an embodiment of the present invention.

FIG. 14 shows a conventional algebraic fixed codebook.

[Explanation of symbols]

 Reference Signs List 200 Preprocessing unit 201 LPC analysis unit 202 LPC quantization unit 203 Synthesis filter 205 Adaptive excitation codebook 206 Quantization gain generation unit 207 Fixed excitation codebook 211 Auditory weighting unit 212 Parameter determination unit 213 Multiplexing unit 301, 401 First Excitation codebooks 302, 402 Second excitation codebook 403 Third excitation codebook 501 Adaptive excitation vector selection unit 502 Fixed excitation vector selection unit 503 Excitation gain quantization unit 601 First fixed excitation vector selection unit 602 Second Fixed sound source vector selection unit 603 Third fixed sound source vector selection unit 604 Selection unit 605 Weighted selection unit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Kazutoshi Yasunaga 3-10-1, Higashi-Mita, Tama-ku, Kawasaki City, Kanagawa Prefecture Inside Matsushita Giken Co., Ltd. No. 1 Nippon Telegraph and Telephone Co., Ltd. (72) Inventor Yuwa Hitozaki Saki 2-1-3 Otemachi, Chiyoda-ku, Tokyo F-term within Nippon Telegraph and Telephone Co., Ltd. 5D045 CA01 DA11 5J064 AA02 BA13 BB12 BC09 BC11 BC16 BC26 BD02

Claims (15)

[Claims] 1. A first excitation codebook having a relatively high temporal resolution that partially represents an excitation vector and a second excitation codebook that has a relatively low temporal resolution that expresses the entire excitation vector. A fixed excitation codebook, characterized in that: 2. A fixed excitation codebook for use in an excitation vector generation apparatus for generating an excitation vector composed of several pulses, wherein each pulse is finely arranged within a limited range with respect to the entire excitation vector. A first excitation codebook storing an excitation vector and a second excitation codebook storing an excitation vector obtained by roughly arranging each pulse over a wide range of the entire excitation vector are provided. Fixed sound source codebook. 3. An excitation codebook in which one pulse is arranged on one of two adjacent samples, wherein different polarities are assigned to both samples. Codebook. 4. The excitation codebook according to claim 2, wherein the excitation codebook arranges a plurality of pulses algebraically, and generates only a combination in which at least two pulses are arranged close to each other. 4. An excitation codebook comprising:
A fixed excitation codebook comprising the excitation codebook according to claim 2 as the second excitation codebook according to claim 2. 5. A fixed excitation codebook according to claim 4 as first and second excitation codebooks, and a third excitation codebook for generating an excitation vector like white noise. Fixed sound source codebook. 6. A fixed excitation codebook used for an excitation vector generation apparatus having a pulse excitation codebook and a noise excitation codebook, wherein the generated excitation vector is a pulse excitation codebook or a noise excitation codebook. When encoding the input signal using the generated excitation vector, which is generated from either one, the excitation vector generated from the noise excitation codebook is more easily selected as the coding distortion is larger. A fixed excitation codebook characterized by being weighted. 7. The apparatus according to claim 5, wherein the first and second excitation codebooks are provided as pulse excitation codebooks, and the third excitation codebook is provided as noise excitation codebooks. The fixed excitation codebook according to claim 6, wherein 8. A first sound source generating step of generating a pulse sound source in which the positions where each pulse can be taken are finely set, and at least two pulses are limited to approach each other, and the possible positions of each pulse. A second sound source generating step of generating a pulse sound source whose position is set roughly and which does not impose any restriction on the combination of each pulse; a third sound source generating step of generating a sound source composed of a random noise signal; A weighting step of performing weighting so that the excitation vector generated in the third excitation generation step is more easily selected as the coding distortion increases. 9. A recording medium which stores a sound source generating program and is readable by a computer, wherein the sound source generating program has finely set positions where each pulse can be taken, and at least two pulses approach each other. A first sound source generation procedure for generating a pulse sound source restricted as described above, and a second sound source generation step for generating a pulse sound source in which the positions where each pulse can be taken are roughly set and the combination of each pulse is not limited at all. , A third excitation generation procedure for generating an excitation composed of random noise signals, and weighting such that the excitation vector generated in the third excitation generation procedure is more easily selected as the coding distortion increases. And a weighting procedure for performing the following. 10. A fixed excitation codebook according to claim 1, an adaptive excitation codebook representing a periodic component of an input speech signal, and a parameter representing a spectrum characteristic of the input speech signal. Means for encoding, means for synthesizing a synthesized speech signal using the excitation vector and the parameter generated from the fixed excitation codebook and the adaptive excitation codebook, an input audio signal and the synthesized audio signal, And a means for determining an output from the fixed codebook and the adaptive codebook such that distortion of the speech is reduced. 11. A fixed excitation codebook according to any one of claims 1 to 7, an adaptive excitation codebook representing a periodic component of a synthesized speech signal, and a spectrum characteristic encoded by the speech encoding device. Means for decoding the parameters to be represented, and the excitation vector determined by the speech encoding apparatus is decoded from the fixed excitation codebook and the adaptive excitation codebook, and a synthesized speech signal is synthesized from the decoded excitation vector and the parameters. A speech decoding device. 12. An audio signal transmission device comprising the audio encoding device according to claim 10. 13. An audio signal receiving apparatus comprising the audio decoding apparatus according to claim 11. 14. A mobile station device comprising at least one of the voice signal transmitting device according to claim 12 and the voice signal receiving device according to claim 13, and performing wireless communication with a base station device. 15. A base station device comprising at least one of the voice signal transmitting device according to claim 12 and the voice signal receiving device according to claim 13, and performing wireless communication with a mobile station device.