JPH11119798A - Method of encoding speech and device therefor, and method of decoding speech and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate background noise with unnatural feeling relaxed by using encoded data by outputting plural kinds of parameters after a predetermined time in a speech encoding process when a judgment result shows background noise section. SOLUTION: An input signal judgment device 21 judges whether an input signal supplied from an input terminal 1 and converted into a digital signal by an A/D converter 10, is voice sound V or unvoiced sound UV or background noise in a predetermined time section. And, an idVUV parameter is outputted which shows the result of V/UV judgment such as '0' presenting unvoiced sound, '1' presenting background noise, '2' presenting 1st voiced sound or '3' presenting 2nd second voiced sound. When a voice encoding device 20 grasps from the judgment result in this input judgment part 21, namely, the idVUV parameter that the input signal is a background noise section, the voice encoding device 20 outputs plural kinds of parameters for UV after a predetermined time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to voice coding for coding an input signal comprising a voice signal section divided into a voiced sound section or an unvoiced sound section and a background noise section at a variable rate based on the determination result of each section. Method and apparatus.

[0002] The present invention also relates to a speech decoding method and apparatus for decoding coded data encoded by the above speech encoding method and apparatus.

[0003]

2. Description of the Related Art In recent years, in a communication field requiring a transmission line, in order to realize effective use of a transmission band, a type of an input signal to be transmitted, for example, a voice signal section divided into a voiced sound or an unvoiced sound section. According to such a type as a background noise section, it has been considered that the transmission is performed after changing the coding rate.

[0004] For example, if it is determined that the background noise section is present, it has been considered that the decoding apparatus does not transmit any coding parameter and simply mutes the image without generating background noise.

[0005] However, in this case, if the communication partner is making a voice, the voice has background noise, but if the voice is not made, the voice suddenly becomes silent. I will.

For this reason, in the variable rate codec, if it is determined that the background noise section is present, some of the coding parameters are not sent, and the decoding apparatus generates background noise by repeatedly using past parameters. Had gone.

[0007]

As described above, when the past parameters are repeatedly used as they are,
The noise itself has the impression of having a pitch, and often results in unnatural noise. This means that even if you change the level,
This happens as long as the line spectrum pair (LSP) parameters are the same.

Even if other parameters are changed by random numbers or the like, if the LSP parameters are the same, an unnatural feeling is given.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a speech encoding method and apparatus for efficiently implementing variable rate encoding.

Further, the present invention has been made in view of the above-mentioned circumstances, and uses a coded data coded by a voice coding method and apparatus for realizing variable rate coding to reduce background noise. It is an object of the present invention to provide a speech decoding method and apparatus capable of generating a sound with reduced feeling.

[0011]

SUMMARY OF THE INVENTION A speech encoding method according to the present invention is characterized in that an input signal consisting of a speech signal section divided into a voiced sound section or an unvoiced sound section, and an input signal comprising a background noise section is variable based on the judgment result of each section. A speech encoding method for encoding at a rate, wherein in order to solve the above-described problem, the input signal is divided into predetermined encoding units on a time axis and encoded in each encoding unit to perform a plurality of types. And outputting the plurality of types of parameters after a predetermined time when the determination result indicates the background noise section.

Here, in the voice encoding step, the determination result of each section is always output as a basic parameter even during the predetermined time.

Further, the speech encoding step includes a short-term prediction residual calculating step of obtaining a short-term prediction residual of the input signal, a sine wave analysis encoding step of performing a sine wave analysis encoding of the obtained short-term prediction residual, or And a waveform encoding step of encoding the input signal by waveform encoding.

When the voice signal section is voiced, the input signal is coded by the sine wave analysis coding step, and when the voice signal section is unvoiced, the input signal is coded by the waveform coding step.

Further, in the speech encoding step, when the background noise section is within the background noise section or one frame before is the background noise section, difference quantization is not performed in the short-term prediction residual calculation step.

A speech encoding apparatus according to the present invention is a speech encoding apparatus for encoding an input signal consisting of a speech signal section divided into a voiced sound section or an unvoiced sound section and a background noise section at a variable rate based on the determination result of each section. In the encoding device, in order to solve the above-described problem, the input signal is divided into predetermined coding units on the time axis, and the coding is performed in each coding unit to perform a plurality of types of speech coding parameters. And a speech encoding unit that outputs the plurality of types of parameters after a predetermined time when the determination result indicates the background noise section.

In the speech decoding method according to the present invention, an input signal consisting of a speech signal section divided into a voiced sound section or an unvoiced sound section and an input signal comprising a background noise section is encoded and transmitted at a variable rate based on a result of determination of each section. A speech decoding method for decoding speech encoded data that has been performed. In order to solve the above-described problem, during the background noise section, a plurality of types of parameters transmitted at predetermined time intervals are used. The background noise is generated using the parameters transmitted in the past during the predetermined time.

For this reason, the past, for example, the linear prediction coding parameter is not used repeatedly as it is, but is used while interpolating with the linear prediction coding parameter sent in the past, so that the unnatural feeling of the background noise can be reduced. .

The speech coded data includes a short-term prediction residual calculation step for obtaining a short-term prediction residual of the input speech signal, and a sine-wave analysis coding for performing sine-wave analysis coding on the obtained short-term prediction residual. And a waveform encoding step of encoding the input audio signal by a waveform encoding step.

The coded voice data is coded by the sine wave analysis coding step when the voice signal section is voiced, and is coded by the waveform coding step when the voice signal section is unvoiced.

The past parameter used to generate background noise during the predetermined time may be at least a short-term prediction coding coefficient calculated by the short-term prediction residual calculation step.

Further, the background noise is generated in accordance with a difference between a previous value of an encoded output from the waveform encoding step and a previous value of the plurality of types of parameters transmitted at the predetermined time. Here, the encoded output from the waveform encoding step is a gain index based on the short-term predicted encoding coefficient.

The speech decoding apparatus according to the present invention encodes an audio signal section divided into a voiced sound section or an unvoiced sound section and an input signal composed of a background noise section at a variable rate based on the determination result of each section and transmits the encoded signal. A speech decoding device for decoding encoded speech encoded data, wherein in order to solve the above-mentioned problem, during the background noise section, a plurality of types of parameters transmitted at predetermined time intervals are used. Speech decoding means for generating the background noise by using the parameters transmitted in the past during the predetermined time.

For this reason, the past, for example, the linear prediction coding parameter is not repeatedly used as it is, but is used while interpolating with the linear prediction coding parameter sent in the past, so that the unnatural feeling of the background noise can be reduced. .

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the speech encoding method and apparatus and speech decoding method and apparatus according to the present invention will be described below.

In this embodiment, a speech encoding method and apparatus and a speech decoding method and apparatus according to the present invention are shown in FIG.
As shown in FIG. 1, a mobile phone device used as a voice encoding device 20 and a voice decoding device 31.

In this portable telephone device, the speech encoding apparatus 20 to which the speech encoding method according to the present invention is applied includes a speech signal section divided into a voiced (Voiced: V) or unvoiced (UnVoiced: UV) section; Background noise (Back grand noi
ze: BGN) is a speech encoding apparatus that encodes an input signal composed of sections at a variable rate based on the determination result of each section. Encoding is performed in units of encoding, and a plurality of types of speech encoding parameters are output.

When the determination result indicates the background noise section, the speech coding apparatus 20 outputs the plurality of types of parameters after a predetermined time. The parameter indicating the determination result is always output as a basic parameter or a mode bit even during the predetermined time.

Here, the input signal determination section 21 determines whether the input signal is a voiced (V) or unvoiced (UV) section or a background noise (BGN) section.

That is, the input signal determination device 21
An input signal supplied from the input terminal 1 and converted to a digital signal by the A / D converter 10 is a voiced sound (V), an unvoiced sound (UV), or a background noise (BGN) in a predetermined time interval. It is determined whether there is. Then, "0" indicating the unvoiced sound, "1" indicating the background noise, "2" indicating the first voiced sound, or the second.
An idVUV parameter indicating the result of the V / UV determination “3” indicating voiced sound is output. The idVUV parameter is set as a basic parameter or a mode bit as described above, and is always output even during the predetermined time.

When the speech coder 20 recognizes that the input signal is in the background noise section based on the result of the determination by the input signal determiner 21, that is, the idVUV parameter, the speech coder 20 waits for a predetermined time. And U
A plurality of types of parameters for V are output.

In this portable telephone device, a speech decoding apparatus 31 to which the speech decoding method according to the present invention is applied.
Encodes an input signal consisting of a voice signal section divided into a voiced sound section or an unvoiced sound section and an input signal consisting of a background noise section at a variable rate based on the determination result of each section and decodes the transmitted voice coded data. A speech decoding device, wherein during the background noise section, the background noise is generated using a plurality of types of parameters transmitted at a predetermined time, and the background noise is transmitted in the past during the predetermined time. The background noise is generated using parameters.

In addition, this portable telephone device, when transmitting,
The audio signal input from the microphone 1 is converted into a digital signal by the A / D converter 10, subjected to variable rate encoding based on the idVUV parameter by the audio encoding device 20, and transmitted by the transmission line encoder 22. After encoding so that the quality of the transmission path is not affected by the voice quality,
The signal is modulated by the modulator 23, the output bit is subjected to transmission processing by the transmitter 24, and transmitted to the antenna 26 through the antenna duplexer 25.
Send from.

At the time of reception, the radio wave captured by the antenna 26 is received by the receiver 27 through the antenna duplexer 25, demodulated by the demodulator 29, the transmission path decoder 30 corrects the transmission path error, and The signal is decoded by a decoding device 31, converted back to an analog audio signal by a D / A converter 32, and output from a speaker 33.

The control unit 34 controls the above units, and the synthesizer 28 controls the transmission / reception frequency by the transmitter 24,
And the receiver 27. The keypad 35 and the LCD display 36 are used for a man-machine interface.

Next, a speech code for encoding an input signal consisting of a speech signal section divided into a voiced sound section or an unvoiced sound section and a background noise section at a variable rate based on the judgment result idVUV parameter of the input signal judgment section 21. The chemical conversion device 20 will be described.

First, the variable rate encoding will be described. As shown in Table 1 below, the LSP quantization index and the excitation parameter index are 20 ms per frame when the idVUV determination parameter is “1” for background noise.
0 bits per ec. When the idVUV determination parameter is an unvoiced sound of “0” and a voiced sound of “2, 3”, the bits are directly set to 18 bits and 20 bits per 20 mseec. Thereby, variable rate encoding can be realized.

[0038]

[Table 1]

Here, V in the idVUV determination parameter
Two bits serving as the / UV determination output are always encoded. The excitation parameter index at the time of unvoiced sound includes a shape index of a codebook of a random codebook described later and a gain index.

FIGS. 2 and 3 show the configuration of this speech coding apparatus. The basic concept of the speech encoding device 20 in FIG.
Sine wave analysis (sinusoidal analysis) is performed by obtaining a short-term prediction residual of the input speech signal, for example, an LPC (linear predictive coding) residual.
s) coding, for example harmonic coding (harmon coding)
ic coding), and a second encoding unit 120 that encodes the input audio signal by waveform encoding that performs phase transmission on the input audio signal. : Voiced) is encoded by the first encoding unit 11
The second encoding unit 120 is used to encode the unvoiced (UV) portion of the input signal using 0.

The first encoding unit 110 has, for example, L
Harmonic coding and multi-band excitation (M
A configuration for performing sine wave analysis encoding such as BE) encoding is used. The second encoding unit 120 employs, for example, a configuration of code excitation linear prediction (CELP) encoding using vector quantization by closed-loop search for an optimal vector using an analysis method based on synthesis.

In the example of FIG. 2, the audio signal supplied to the input terminal 101 is sent to the LPC inverse filter 111 and the LPC analysis / quantization unit 113 of the first encoding unit 110. The LPC coefficient or the so-called α parameter obtained by the LPC analysis / quantization unit 113 is
The LPC inverse filter 111 extracts the linear prediction residual (LPC residual) of the input audio signal. Also, a quantized output of an LSP (line spectrum pair) is extracted from the LPC analysis / quantization unit 113 and sent to the output terminal 102 as described later. The LPC residual from LPC inverse filter 111 is sent to sine wave analysis encoding section 114. In the sine wave analysis coding unit 114, pitch detection and spectrum envelope amplitude calculation are performed, and the idVUV parameter of the input signal is obtained by the input signal determination unit 115 having the same configuration as the input signal determination unit 21. The spectrum envelope amplitude data from the sine wave analysis encoding unit 114 is sent to the vector quantization unit 116. The codebook index from the vector quantization unit 116 as the vector quantization output of the spectrum envelope is sent to the output terminal 103 via the switch 117, and the pitch output from the sine wave analysis encoding unit 114 is sent via the switch 118. Output terminal 104
Sent to Also, idVUV from the input signal determination unit 115
The judgment parameter output is sent to the output terminal 105, and the switches 117 and 118 and the switch 1 shown in FIG.
Used for 19 control signals. Switches 117, 118
Selects the index and the pitch when the voiced sound (V) is received by the control signal, and selects the output terminals 103 and 104
Output from each.

In the vector quantization performed by the vector quantization unit 116, for example, the amplitude data of one effective band on the frequency axis is compared with the first data in the block from the last data in the block. dummy data as to interpolate values up to data, or the last data and the first data of the last and first added by an appropriate number of data number of dummy data as to extend the after expanding the N _F ,
Obtain an amplitude data of O _S times the number by performing oversampling O _S times the band-limited (e.g., 8 times), amplitude data of O _S times the number _{((m MX +1) × O} S pieces) Is linearly interpolated into N _M more (eg, 20
48), the N _M pieces of data are thinned out, converted into the above-mentioned fixed number M (for example, 44 pieces), and then vector-quantized.

The second encoding unit 120 in FIG. 2 has a CELP (Code Excitation Linear Prediction) encoding configuration in this example, and outputs the output from the noise codebook 121 using a weighted synthesis filter 122. The synthesized voice signal is sent to the subtractor 123, and the audio signal supplied to the input terminal 101 is extracted from the audio signal obtained through the auditory weighting filter 125. 12
4 to calculate the distance, and search for a vector that minimizes the error in the noise codebook 121 by using a closed-loop search using an analysis by synthesis method. Vector quantization is performed. This CELP coding is used for coding the unvoiced sound portion as described above,
The codebook index as UV data from No. 1 is turned on when the idVUV determination parameter from the input signal determination unit 115 is unvoiced (UV).
Through the output terminal 107.

Further, id which is a control signal for the switch 127
When the VUV determination parameter is “1” and the input signal is determined to be a background noise signal, a plurality of parameters at the time of unvoiced sound after a predetermined time, for example, 8 frames,
For example, a shape index or a gain index as UV data from the noise codebook 121 is sent.

Next, a more specific configuration of the audio signal encoding apparatus shown in FIG. 2 will be described with reference to FIG. In FIG. 3, parts corresponding to the respective parts in FIG. 2 are denoted by the same reference numerals.

In the audio signal encoding apparatus shown in FIG. 3, the audio signal supplied to input terminal 101 has been subjected to filter processing for removing signals in unnecessary bands by high-pass filter (HPF) 109. After that, the LPC analysis circuit 132 of the LPC (linear prediction coding) analysis / quantization unit 113
To the LPC inverse filter circuit 111.

The LPC analysis circuit 132 of the LPC analysis / quantization unit 113 obtains a linear prediction coefficient, that is, an α parameter by an autocorrelation method by applying a Hamming window with a length of about 256 samples of the input signal waveform as one block. .
The framing interval, which is the unit of data output, is 160
Make it about a sample. When the sampling frequency fs is, for example, 8 kHz, one frame interval is 20 for 160 samples.
msec.

The α parameter from the LPC analysis circuit 132 is sent to the α → LSP conversion circuit 133 and is converted into a line spectrum pair (LSP) parameter. This converts the α parameter obtained as a direct type filter coefficient into, for example, ten, ie, five pairs of LSP parameters. The conversion is performed using, for example, the Newton-Raphson method. The conversion to the LSP parameter is because it has better interpolation characteristics than the α parameter.

The LSP parameters from the α → LSP conversion circuit 133 are subjected to matrix or vector quantization by the LSP quantizer 134. At this time, the LSP quantizer 134 may perform difference vector quantization (difference VQ) having a leaking factor. The quantization efficiency of the difference VQ is superior to that of the matrix quantization (MQ), and since the quantization error is not biased to one frame as in the case of MQ, a smooth voice with less noise is obtained. . However, once an error occurs in the differential VQ,
Since the effect continues for a while, the leak amount of the difference is set to be large. However, the input signal determination unit 115
When the background noise is determined, the LSP is not transmitted, and the LSP quantizer 134 does not perform the difference VQ, which is a type of difference quantization.

The quantized output from the LSP quantizer 134, that is, the index of LSP quantization, is
19, and then retrieved via terminal 102 and the quantized LSP vector is LS
The signal is sent to the P interpolation circuit 136. Here, the switch 119
The switching of is controlled by the idVUV determination flag from the input signal determination unit 115, and is turned on when, for example, a voiced sound (V).

The LSP interpolation circuit 136 has a
The vector of the LSP quantized for each c is interpolated to make the rate 8 times. That is, the LSP vector is updated every 2.5 msec. This is because when the residual waveform is analyzed and synthesized by the harmonic encoding / decoding method, the envelope of the synthesized waveform becomes a very smooth and smooth waveform, so that an abnormal sound is generated when the LPC coefficient changes abruptly every 20 msec. This is because there are times. That is, if the LPC coefficient is gradually changed every 2.5 msec, the occurrence of such abnormal noise can be prevented.

In order to perform inverse filtering of the input voice using the LSP vector every 2.5 msec in which such interpolation has been performed, the LSP → α conversion circuit 137
The LSP parameter is converted into, for example, an α parameter which is a coefficient of a direct-order filter of about the tenth order. This LSP → α
The output from the conversion circuit 137 is sent to the LPC inverse filter circuit 111, where the LPC inverse filter 111
Inverse filtering is performed using the α parameter updated every 2.5 msec to obtain a smooth output. An output from the LPC inverse filter 111 is output to an orthogonal transform circuit 145 of a sine wave analysis encoding unit 114, specifically, for example, a harmonic encoding circuit, for example, a DFT.
(Discrete Fourier Transform) sent to the circuit.

The α parameter from the LPC analysis circuit 132 of the LPC analysis / quantization unit 113 is sent to a perceptual weighting filter calculating circuit 139 to obtain data for perceptual weighting. Vector quantizer 116 and the second encoding unit 12
0 and a synthesis filter 122 with a perceptual weight.

The sine wave analysis encoding unit 114 such as a harmonic encoding circuit analyzes the output from the LPC inverse filter 111 by a harmonic encoding method. That is, pitch detection, calculation of the amplitude Am of each harmonic, determination of voiced sound (V) / unvoiced sound (UV) are performed, and the number of the envelopes or amplitudes Am of the harmonics that change with the pitch is dimensionally converted to a constant number. .

In the specific example of the sine wave analysis encoding unit 114 shown in FIG. 3, general harmonic encoding is assumed. In particular, in the case of MBE (Multiband Excitation) encoding, Modeling is performed on the assumption that a voiced portion and an unvoiced portion exist in the frequency domain at the same time (in the same block or frame), that is, for each band. In other harmonic coding, an alternative determination is made as to whether voice in one block or frame is voiced or unvoiced. In the following description, the term “V / UV for each frame” means that when all bands are UV when applied to MBE coding, the UV of the frame is used. Regarding the MBE analysis / synthesis technique, detailed specific examples are disclosed in the specification and drawings of Japanese Patent Application No. 4-91422 previously proposed by the present applicant.

The open-loop pitch search section 141 of the sine wave analysis encoding section 114 shown in FIG.
01 and the zero-cross counter 1
Signals from the HPF (high-pass filter) 109 are supplied to 42 respectively. The LPC residual or the linear prediction residual from the LPC inverse filter 111 is supplied to the orthogonal transform circuit 145 of the sine wave analysis encoding unit 114. In the open loop pitch search section 141,
An LPC residual of the input signal is used to perform a relatively rough pitch search by an open loop, and the extracted coarse pitch data is sent to a high-precision pitch search 146, and a high-precision closed loop as described later is used. A pitch search (fine search of the pitch) is performed. From the open loop pitch search section 141, a normalized autocorrelation maximum value r (p) obtained by normalizing the maximum value of the autocorrelation of the LPC residual with power together with the coarse pitch data is extracted.
The signal is sent to the input signal determination unit 115.

The orthogonal transform circuit 145 performs an orthogonal transform process such as DFT (Discrete Fourier Transform) to convert the LPC residual on the time axis into spectrum amplitude data on the frequency axis. An output from the orthogonal transform circuit 145 is output to a high-precision pitch search unit 146 and a spectrum evaluation unit 148 for evaluating a spectrum amplitude or an envelope.
Sent to

High precision (fine) pitch search section 146
Is supplied with relatively rough coarse pitch data extracted by the open loop pitch search unit 141 and data on the frequency axis, for example, DFT performed by the orthogonal transform unit 145. The high-precision pitch search unit 146 oscillates ± several samples at intervals of 0.2 to 0.5 around the coarse pitch data value to drive the value of the fine pitch data with a decimal point (floating) to an optimum value. At this time, as a method of fine search, a so-called analysis by synthesis method is used, and the pitch is selected so that the synthesized power spectrum is closest to the power spectrum of the original sound. The pitch data from the high-precision pitch search unit 146 by such a closed loop is output via the switch 118 to the output terminal 10.
4

The spectrum evaluation section 148 evaluates the magnitude of each harmonic and the spectrum envelope which is a set of the harmonics based on the spectrum amplitude and the pitch as the orthogonal transform output of the LPC residual, and outputs a high-precision pitch search section 146 and a hearing weight. Is sent to the vector quantizer 116 with

The input signal determination section 115 receives the normalized autocorrelation maximum value r from the open loop pitch search section 141.
Based on (p) and the zero cross count value from the zero cross counter 142, determine whether the frame is the voiced sound, unvoiced sound, or background noise, and output the idVUV determination parameter. I do. The idVUV determination parameter from the input signal determination unit 115 is extracted via the output terminal 105 and, as described above, the switch 119, the switch 117, and the switch 117.
18 and 127 are also used as switching control signals.

Incidentally, a data number conversion (a kind of sampling rate conversion) section is provided at the output section of the spectrum evaluation section 148 or the input section of the vector quantizer 116. The number-of-data converters are used to make the amplitude data | A _m | of the envelope a constant number in consideration of the fact that the number of divided bands on the frequency axis varies according to the pitch and the number of data varies. It is. That is, for example, if the effective band is up to 3400 kHz, this effective band is divided into 8 bands to 63 bands according to the pitch, and the amplitude data | A _m | of each of these bands is obtained. The number m _MX +1 also changes from 8 to 63. For this reason, in the data number converter, the variable number m _MX +1 of amplitude data is set to a fixed number M, for example, 44,
Is converted to data.

The fixed number M (for example, 44) of the amplitude data or envelope data from the output unit of the spectrum evaluation unit 148 or the data number conversion unit provided at the input unit of the vector quantizer 116 is a vector quantization unit. The data is grouped into a vector by a predetermined number, for example, 44 pieces of data, and weighted vector quantization is performed. This weight is given by the output from the auditory weighting filter calculation circuit 139. The envelope index from the vector quantizer 116 is:
It is taken out from the output terminal 103 via the switch 117. Prior to the weighted vector quantization, an inter-frame difference using an appropriate leak coefficient may be calculated for a vector composed of a predetermined number of data.

Next, the second encoding section 120 will be described. The second encoding unit 120 has a so-called CELP (Code Excited Linear Prediction) encoding configuration, and is particularly used for encoding an unvoiced sound portion of an input audio signal. In this unvoiced CELP coding configuration,
A noise output corresponding to an LPC residual of unvoiced sound, which is a representative value output from a noise codebook, that is, a so-called stochastic codebook 121, is passed through a gain circuit 126 to a synthesis filter 1 with auditory weights.
22. The weighted synthesis filter 122 performs an LPC synthesis process on the input noise, and sends the obtained weighted unvoiced sound signal to the subtractor 123. A signal obtained by subjecting the audio signal supplied from the input terminal 101 via the HPF (high-pass filter) 109 to auditory weighting by the auditory weighting filter 125 is input to the subtractor 123, and the difference from the signal from the synthesis filter 122 is input to the subtractor 123. Alternatively, the error is extracted. It is assumed that the zero input response of the synthesis filter with auditory weight is subtracted from the output of the auditory weight filter 125 in advance. This error is sent to the distance calculation circuit 124 to calculate the distance, and a representative value vector that minimizes the error is searched in the noise codebook 121. Analysis by Sy
Vector quantization of the time axis waveform is performed using a closed loop search using the nthesis) method.

The data for the UV (unvoiced sound) portion from the second encoding unit 120 using the CELP encoding configuration includes the shape index of the codebook from the noise codebook 121 and the code from the gain circuit 126. The gain index of the book is extracted. Noise codebook 121
Is sent to the output terminal 107s via the switch 127s, and the gain index which is UV data of the gain circuit 126 is sent to the output terminal 107g via the switch 127g.

Here, these switches 127s, 12s
7g and the switches 117 and 118 are turned on / off by the idVUV determination parameter from the input signal determination unit 115.
The switches 117 and 118 are turned off when the idVUV determination parameter of the audio signal of the frame to be transmitted is voiced (V), and the switches 117 and 118 are turned on.
127g is turned on when the audio signal of the frame to be transmitted at present is unvoiced (UV). When the idVUV determination parameter indicates background noise, the switch 127 is used.
s and 127g are turned on every eight frame times, and output the shape index and the gain index. The switch 119 is also turned on every eight frame time, and outputs the UV LSP index. These are a plurality of types of parameters for UV described above.

FIG. 4 shows a detailed configuration of the input signal determination section (referred to as an input signal determination device) 115 in the figure.
That is, the input signal determination unit 115 detects the minimum level of the input signal (effective value) input from the input terminal 1 via the effective (root mean square, rms) value calculation unit 2 in a predetermined time interval, for example, 20 msec. A minimum level calculator 4 for holding the minimum level; and a reference level calculator 5 for calculating a reference level from the effective value of the input signal from the effective value calculator 2 by calculation. Based on the minimum level and the reference level from the reference level calculation unit 5, the input signal is voiced (Voice) or unvoiced (UnV) in a predetermined time interval.
oice) or background noise. Then, “0” indicating the unvoiced sound, “1” indicating the background noise, “2” indicating the first voiced sound, or “3” indicating the second voiced sound And outputs an idVUV parameter indicating the result of the V / UV determination.

Further, the input signal determination device 21 temporarily determines whether the input signal effective value from the effective value calculation section 2 is voiced (V) / unvoiced (UV) for a predetermined time section. A UV judgment unit 3 is provided.
Supply UV judgment result. The minimum level calculator 4 calculates the minimum level based on the V / UV determination result.

The V / UV determination result from the V / UV determination unit 3 is also supplied to the parameter generation unit 8. The parameter generator 8 outputs the idVUV parameter from the output terminal 105.

The parameter generation unit 8 includes the minimum level from the minimum level calculation unit 4 and the reference level calculation unit 5.
The idVUV parameter is output based on the comparison result from the comparison unit 7 for comparing the reference level with the reference level and the V / UV determination result from the V / UV determination unit 3.

The operation of the input signal determination device 21 will be described below. For example, in a running train,
Background noise level is high. Therefore, it is desirable to determine the threshold value according to the surrounding noise.

Therefore, the minimum level calculating section 4 sets the smallest level in an appropriate predetermined time interval as the minimum level, and updates the minimum level every predetermined time.

FIG. 5 is a flowchart showing the algorithm of the minimum level calculation unit 4. In this flowchart, the updating (tracking) of the minimum level is roughly divided into the setting and clearing of the minimum level candidate value cdLev and the setting and clearing of the minimum level gml.

First, in step S1, the V / UV determination unit 3
It is determined whether or not the number of continuous voiced frame frames vCont is an integer greater than 4 based on the V / UV determination result from. That is, it is determined whether or not the frame determined to be voiced sound V is an integer number of times greater than 4, that is, five consecutive frames.
Here, when five or more voiced sound frames are continuous, it is determined that the voice section is in the voice section, and step S2 is performed.
To clear the minimum level candidate value cdLev. In this step S2, the number of times the candidate value has been set gmlSetSt
ate is 0. On the other hand, if it is determined in step S1 that the number of continuous voiced frames vCont is 4 or less, the process proceeds to step S3.

At step S3, it is determined whether or not the input level lev of the current input signal via the effective value calculating section 2 is smaller than the minimum value MIN_GML of the minimum level. Here,
The minimum value MIN_GML of the minimum level is determined so that the minimum level gml does not become zero. Where the input level lev
Is smaller than the minimum value MIN_GML of the minimum level, the minimum value MIN_GML of the minimum level is set as the minimum level gml in step S4. In this step S4, the number of times that the candidate value has been set, gmlSetState, and the number of times that the candidate value has not been set after the minimum level has been set
gmlResetState is 0. On the other hand, if it is determined in step S3 that the current input level lev is equal to or more than the minimum minimum value MIN_GML, the process proceeds to step S5.

In step S5, the current input level lev
Is smaller than the minimum level gml. If “YES” here, the process proceeds to a step S6. That is, in step S6, when the current input level lev is equal to or more than the minimum minimum value MIN_GML in the determination in step S3, and when the current input level lev is determined to be smaller than the minimum level gml in step S5. , The input level lev is set as the minimum level gml. On the other hand, if it is determined in step S5 that the current input level lev is equal to or higher than the minimum level gml, the process proceeds to step S7.

In the step S7, it is determined whether or not the current input level is sufficiently small and whether or not the fluctuation with the candidate value cdLev is small. In this step S7, it is determined whether the current input level is sufficiently small or the variation with the candidate value cdLev is small based on whether or not the status is status0. status0
Is sufficiently small such that the input level lev is 100.0 or less, or the candidate value cdLev * 0.70 when the input level is 500.0 or less.
This is a state indicating that the fluctuation from the candidate value cdLev is small, such as being larger and smaller than the candidate value cdLev * 1.30. Here, if YES is selected and it is determined that the current input level is sufficiently small or the variation from the candidate value cdLev is small, the candidate value cdLev is updated. On the other hand, if NO is selected, the process proceeds to step S11.

In step S8, it is determined whether or not the number of times gmlSetState in which the candidate value cdLev is continuously updated is 7 or more, that is, whether or not the update of the candidate value cdLev is continued for seven frames. If it is determined that the update of the candidate value cdLev has continued for seven or more frames, the process proceeds to step S9, and the input level lev at that time is set to the minimum level gml. Candidate value cd
If the update of Lev is within six frames, the result is NO, and the input level lev is set to the candidate value cdLev in step S10.

On the other hand, in step S11, which proceeds after the determination in step S7 is NO, it is determined whether or not the change between the input level prevLev one frame before and the current input level lev is small. Input level pr one frame before
The determination as to whether or not the fluctuation between evLev and the current input level lev is small is made by determining whether or not the status is status1. stat
us1 is sufficiently small such that the current input level lev is equal to or less than 100.0, or is larger than the input level prevLev * 0.70 in the past one frame when the current input level lev is 500.0 or less and the input level prevLev * 1.30 in the past one frame Input level prev one frame past, such as less than
This is a state indicating that the fluctuation from Lev is small. here,
If YES is selected and the current input level is sufficiently small or the change between the input level one frame past and the current input level is small, the process proceeds to step S12, where the current input level lev is set to the minimum level candidate value cdLev. Set to. On the other hand, if it is determined in step S11 that the current input level is not low or that the change between the input level one frame past and the current input level is not small, the process proceeds to step S13.

In step S13, after the minimum level is set, the number of times no candidate value is set gmlResetState
Is greater than 40. Here, the result is NO and the number of times the candidate value has not been set gmlResetState is 40
If not, the minimum level candidate value cdLev is cleared in step S14, and a predetermined minimum value is set.
On the other hand, if "YES" here, and it is determined that the number of times gmlResetState in which no candidate value has been set exceeds 40, the process proceeds to step S15, and the minimum level gml is set to the minimum value MIN_GML of the minimum level.

As described above, the minimum level is held for a certain period of time and is sequentially updated.

Next, the operation of the reference level calculator 5 will be described with reference to FIG. The reference level calculation unit 5 converts the reference level refLev into the following (1)
It is calculated by the formula.

RefLev = A × max (lev, refLev) + (1.0−A) × min (lev, refLev) (1) In the equation (1), A = 0.
Input level lev and reference level r when 75
FIG. 6 shows the relationship with efLev. Reference level refLe
v rises at the rising edge like the input level lev, but gradually decreases at the falling edge. For this reason,
By using the reference level, it is possible to prevent a state in which the level is instantaneously lowered in the audio signal section from being determined as a background noise section. As described above, the reference level calculation unit 5 calculates a smooth level that allows a certain margin even for an instantaneous level change.

The comparison unit 7 calculates B × gml obtained by multiplying the minimum level from the minimum level calculation unit 4 by a predetermined constant B and the reference level refLev from the reference level calculation unit 5.
Compare with Then, the comparison result is sent to the parameter generation unit 8.

The parameter generation unit 8 includes the V / UV determination unit 3
With respect to the frame determined to be V according to the determination result in step (1), it is checked whether or not the reference level refLev shown in the above equation (1) is smaller than B times the minimum level gml. However, past V /
The UV judgment is checked, and when two or more V frames are continuous, it is assumed that the voice section has started, and no judgment is made as a background noise section. That is, when it is determined that the current frame is V, it is checked whether or not the past V frames are continuous, and if it is continuous, the apparatus does not enter the background noise mode. This is because if the background noise mode is entered while V frames are continuous, a sense of discontinuity occurs.

The parameter generation unit 8 sets the reference level refLev for the frame whose determination result from the V / UV determination unit 3 is determined to be UV, as in the case of V.
Is smaller than B times the minimum level gml, and if this condition is satisfied four times, it is determined to be a background noise section. In other words, when it is determined that the condition is UV, the condition is satisfied for four consecutive frames, and then the background noise section is determined.

Note that B is an appropriate constant, and is set to 2.0 here. It is also conceivable to use an amount proportional to the variance of the input level lev instead of such a constant.

Then, the parameter generator 8 outputs the idVUV parameter from the output terminal 105.

As described above, the input signal judging device 21
Updates the minimum level gml, and based on that, the threshold gm between the audio signal section and the background noise section
Since l × B can be changed, by comparing the threshold gml × B with the reference level refLev, it is possible to distinguish the speech signal section from the background noise section with high accuracy.

Now, return to FIG. Voice decoding device 31
Transmits the coded data variable-rate coded by the voice coding device 20 of another mobile phone device to the antenna 2
6. The signal is received and decoded through the antenna duplexer 25, the receiver 27, the demodulator 29 and the transmission path decoder 30.

As described above, the speech decoding device 31 decodes the coded data based on the idVUV determination parameter which is always transmitted from the speech encoding device 20 during the predetermined time. In particular, if the idVUV determination parameter is “1” indicating a background noise section, the plurality of types of parameters transmitted at intervals of eight frames, for example, a shape index of a noise codebook, a gain index, or an LSP parameter are used. In addition to generating background noise, the background noise is generated by interpolating a line spectrum pair (LSP) parameter transmitted in the past in eight frames.

Actually, in the speech decoding device 31, always,
LSP sent last time (prevLsp1) and LS sent two times before
P (prevLsp2) is held in, for example, a RAM.

When the idVUV determination parameter enters the background noise mode, no new LSP is sent, so that prevLsp1 and prevLsp2 are updated, and the two LSs are updated.
By linearly interpolating P, the LSP of the current frame
To form background noise.

In the background noise mode, all the UV parameters are sent from the speech coding apparatus side as normal UV in the eighth frame. At this time, the gain index from the gain circuit 126 is checked, and the index is sent last time. If the index is smaller than the index +2, the LSP used for synthesizing the frame is replaced with the previously transmitted parameter. This operation will be described later. However, it is assumed that the gain indexes are sorted in ascending order.

FIG. 7 and FIG. 8 show the configuration of such a speech decoding device 31. FIG. 7 is a block diagram showing a basic configuration of the audio decoding device 31.

In FIG. 7, a codebook index as a quantized output of the LSP (line spectrum pair) from the output terminal 102 of FIG. 2 is input to an input terminal 202. The input terminals 203, 204, and 205 include the output terminals 103, 104, and 105 of FIG.
, That is, an index, a pitch, and a V / UV determination output as an envelope quantization output. An index as UV (unvoiced sound) data from the output terminal 107 in FIG. 2 is input to the input terminal 207.

The index as the envelope quantization output from the input terminal 203 is calculated by the inverse vector quantizer 212.
, And is subjected to inverse vector quantization, and the spectrum envelope of the LPC residual is obtained and sent to the voiced sound synthesis unit 211. The voiced sound synthesizer 211 synthesizes an LPC (linear predictive coding) residual of the voiced sound part by sine wave synthesis.
And 205 and the pitch and idVUV determination parameters are also provided. LP of voiced sound from voiced sound synthesizer 211
The C residual is sent to LPC synthesis filter 214. The index of the UV data from the input terminal 207 is
It is sent to the unvoiced sound synthesis unit 220, and the LPC residual of the unvoiced sound portion is extracted by referring to the noise codebook. This LPC residual is also sent to the LPC synthesis filter 214.
In the LPC synthesis filter 214, the LP of the voiced sound portion is
The C residual and the LPC residual of the unvoiced part are independent of each other,
An LPC synthesis process is performed. Alternatively, the voiced sound portion L
LPC synthesis processing may be performed on the sum of the PC residual and the LPC residual of the unvoiced sound portion. Here, the index of the LSP from the input terminal 202 is LPC
The parameter is sent to the parameter reproducing unit 213 to extract the α parameter of the LPC, which is sent to the LPC synthesis filter 214. An audio signal obtained by LPC synthesis by the LPC synthesis filter 214 is extracted from the output terminal 201.

Here, idVU supplied to the input terminal 205
V judgment parameter and the above U supplied to the input terminal 207
The shape index and the gain index of the random codebook as V data are obtained by the LPC parameter generation unit 21.
3 is transmitted to the LPC parameter reproduction control section 240 which controls the reproduction of the LPC parameter.

The LPC reproduction section 213 controls the LPC reproduction section 240 to generate an LPC for generating a background noise signal and sends it to the LPC synthesis filter 214.

Next, FIG. 8 shows a more specific configuration of the speech decoding device 31 shown in FIG. This FIG.
In FIG. 7, portions corresponding to the respective portions in FIG. 7 are denoted by the same reference numerals.

In FIG. 8, an input terminal 202 has
L corresponding to the output from the output terminal 102 in FIGS.
An SP vector quantization output, a so-called codebook index, is supplied.

The index of this LSP is calculated by the inverse vector quantizer 231 of the LSP of the LPC parameter reproducing unit 213.
Is subjected to inverse vector quantization into LSP (line spectrum pair) data, sent to LSP interpolation circuits 232 and 233 via a switch 243, and subjected to LSP interpolation processing. At 235, the parameter is converted to an α parameter of LPC (linear prediction code), and the α parameter is sent to the LPC synthesis filter 214. Where L
The SP interpolation circuit 232 and the LSP → α conversion circuit 234 are for voiced sound (V), and the LSP interpolation circuit 233 and the LSP
→ The α conversion circuit 235 is for unvoiced sound (UV). Also L
The PC synthesis filter 214 includes an LPC synthesis filter 236 for a voiced portion and an LPC synthesis filter 23 for an unvoiced portion.
7 is separated. That is, LPC coefficient interpolation is performed independently for voiced and unvoiced parts, and LSPs having completely different properties are interpolated between the transition from voiced to unvoiced and the transition from unvoiced to voiced. To prevent the adverse effects of doing so.

The input terminal 203 shown in FIG. 8 is supplied with the code index data obtained by quantizing the weight of the spectral envelope (Am) corresponding to the output from the terminal 103 on the encoder side shown in FIGS. , Input terminal 204 is supplied with pitch data from terminal 104 in FIGS. 2 and 3, and input terminal 205 is supplied with idVUV determination parameters from terminal 105 in FIGS. 2 and 3. .

The vector-quantized index data of the spectral envelope Am from the input terminal 203 is
The data is sent to the inverse vector quantizer 212, subjected to inverse vector quantization, subjected to an inverse transform corresponding to the above-described data number conversion, becomes spectral envelope data, and becomes a sine wave synthesizing circuit of the voiced sound synthesizer 211. 215.

If the inter-frame difference is obtained prior to the vector quantization of the spectrum at the time of encoding, the inter-frame difference is decoded after the inverse vector quantization here, the number of data is converted, and the spectrum envelope is converted. To get the data.

The sine wave synthesis circuit 215 has an input terminal 2
04 and the idVUV from input terminal 205
Judgment parameters are supplied. Sine wave synthesis circuit 2
15, the LPC inverse filter 1 shown in FIGS.
LPC residual data corresponding to the output from 11 is extracted and sent to the adder 218. The specific method of the sine wave synthesis is disclosed in, for example, the specification and drawings of Japanese Patent Application No. 4-91422 or the specification and drawings of Japanese Patent Application No. 6-198451, which were previously proposed by the present applicant. Have been.

The envelope data from the inverse vector quantizer 212, the pitches from the input terminals 204 and 205, and the idVUV determination parameter are sent to the noise synthesis circuit 216 for adding noise in the voiced (V) portion. Has been sent. The output from the noise synthesis circuit 216 is sent to an adder 218 via a weighted superposition addition circuit 217. This is an excitation (Excitati) which is input to the LPC synthesis filter of voiced sound by sine wave synthesis.
When on (excitation, excitation) is made, there is a case where a low pitch sound such as a male voice has a feeling of stuffy nose, and the sound quality suddenly changes between V (voiced sound) and UV (unvoiced sound) and feels unnatural. Considering a certain point, the LPC synthesis filter input of the voiced sound portion, that is, the excitation, was considered in consideration of parameters based on the speech coded data, for example, pitch, spectrum envelope amplitude, maximum amplitude in a frame, residual signal level, and the like. Noise is added to the voiced portion of the LPC residual signal.

The added output from the adder 218 is sent to the voiced sound synthesis filter 236 of the LPC synthesis filter 214 and subjected to LPC synthesis processing to become time waveform data, and further to the voiced sound post filter 238v.
, And sent to the adder 239.

Next, the input terminals 207s and 207 of FIG.
The shape index and the gain index as UV data from the output terminals 107 s and 107 g in FIG. 3 are supplied to g, and are sent to the unvoiced sound synthesis unit 220. The shape index from the terminal 207s is stored in the noise codebook 221 of the unvoiced sound synthesizer 220 in the terminal 2
The gain index from 07g is sent to the gain circuit 222, respectively. The representative value output read from the noise codebook 221 is a noise signal component corresponding to the LPC residual of the unvoiced sound. The noise signal component has an amplitude of a predetermined gain in the gain circuit 222 and is sent to the windowing circuit 223. A windowing process is performed to smooth the connection with the voiced sound portion.

The output from the windowing circuit 223 is output from the unvoiced sound synthesis section 220 as the LPC synthesis filter 21.
4 is sent to the synthesis filter 237 for UV (unvoiced sound). The synthesis filter 237 performs LPC synthesis processing to obtain unvoiced sound time waveform data. The unvoiced sound time waveform data is filtered by the unvoiced sound post filter 238u, and then sent to the adder 239.

In the adder 239, the time waveform signal of the voiced sound portion from the voiced sound post filter 238v and the time waveform data of the unvoiced sound portion from the unvoiced sound post filter 238u are added, and the result is taken out from the output terminal 201.

Further, inside the LPC parameter reproducing section 213, an LSP interpolation circuit 245 for reproducing the LPC parameter used for generating the background noise signal, and an LSP →
The α conversion circuit 247 is also provided after the switch 243. Further, a RAM 244 for holding the prevLSP1 and prevLSP2 obtained by the inverse quantizer 231 of the LSP is provided with a RAM 244 having an interval of 8 frames.
A frame interpolation unit 245 for correcting interpolation between prevLSP1 and prevLSP2 to a frame interval is also provided.

The α parameter for BGN from the LSP → α conversion circuit 247 is sent to the LPC synthesis filter 237 of the unvoiced sound portion of the LPC synthesis filter 214.

Further, the LPC parameter reproduction control unit 2
40, an index determination unit 242 that determines whether the gain desk for the UV data from the input terminal 207g is smaller than the previously transmitted index +2,
A switching control unit 241 for controlling switching of the switch 243 based on the determination result from the index determining unit 242 and the idVUV determination parameter supplied from the input terminal 205 is provided.

FIG. 9 is a flowchart showing the operation of the speech decoding apparatus 31 when the idVUV determination parameter is 1, that is, when a mode bit serving as the basic parameter indicating a background noise section is received. It will be described using FIG.

First, when the idVUV determination parameter is 1 in step S21, the LPC parameter reproduction control unit 24
0 switch control unit 241
Turn off. Then, the process proceeds to step S22, where the LSP
PrevLS held in the RAM 244 by the interpolation circuit 246
An LSP for BGN is obtained by using a linear interpolation value for each frame obtained from P1 and PrevLSP2 through the frame interpolation circuit 245. Then, the LSP for BGN is supplied to the UV synthesis filter 237, and background noise is synthesized.

Note that, when the number of frames determined to be a background noise section becomes eight consecutive frames, the speech encoding apparatus 20 transmits the shape index, gain index, and LSP parameter for normal UV data in the next ninth frame. Come. Here, in the speech encoding device 20, the idVUV determination parameter does not always become UV at the ninth frame. Therefore, it is necessary for the audio decoding device 31 to determine whether the data is true UV data or simply all the UV parameters sent in the ninth frame.

Therefore, the LPC parameter reproduction control unit 24
In step S23, when idVUV = 0 in step S23, the process proceeds to step S24, in which the index determination unit 242 checks the gain index for the UV data transmitted via the input terminal 207g, and determines whether the routine process in step S26 is performed. It is determined whether the processing is the original UV processing in step S27. Specifically, as described above, it is determined whether or not the gain index for the UV data from the input terminal 207g is smaller than the previously transmitted index +2. If the UV data index sent in the ninth frame is a UV index as audio, it should be larger than the parameter of the gain index sent last time.

If the gain index is smaller than the previously transmitted index +2 in step S24,
This is determined to be the data for the UV data sent in the ninth frame, that is, the data for the routine, and step S2
6 and the switching control unit 241
3 is connected to the LSP interpolation circuit 246 side, and the PrevLSP1
And the value obtained by linear interpolation using PrevLSP2,
LSP sent from LSP inverse quantization unit 231 for UV
The parameters are supplied to the LSP interpolation circuit 246. LSP
The interpolation circuit 246 supplies the updated LSP parameter to the LSP → α conversion circuit 247 as it is. Then, the BGN α parameter from the LSP → α conversion circuit 247 is sent to the LPC synthesis filter 237 of the unvoiced sound portion of the LPC synthesis filter 214, and the ninth frame has a different background noise from the background noise between the eight frames. Is obtained. For this reason, the unnaturalness of the background noise can be reduced.

If the gain index is greater than or equal to the previously transmitted index + 2 in step S24, it is determined that the transmitted ninth frame is a true UV parameter. , Step S2
Go to 7. In step S27, the switching control unit 241
Switches the switch 243 to the LSP interpolation circuit 233 for UV, and obtains L obtained by normal LSP interpolation for UV.
Synthesis of unvoiced sound using SP is performed.

On the other hand, if it is determined in step S23 that the idVUV determination parameter is not 0, the process proceeds to step S25, where the α parameter is converted from the UV LSP, and a voiced sound is synthesized by the synthesis filter 236.

As described above, in the speech decoding device 31,
When the idVUV determination parameter is 1, that is, when the speech coder of another mobile phone device detects a background noise section, the background noise is generated using a plurality of types of parameters transmitted with eight frames apart. Along with
In the eight frames, the background noise is generated by using parameters transmitted in the past. For this reason, the unnaturalness of the background noise can be reduced. Further, even if a true unvoiced sound section is detected and transmitted by chance in the ninth frame, accurate judgment can be made, so that high-quality speech can be decoded.

Although the LSP has a delay of eight frames, the connection is completely smooth during the background noise mode, and the LSP does not suddenly change to generate abnormal noise. Further, since the consonant part of the voice often has a higher level than the background noise, it is possible to prevent the consonant part of the voice from being erroneously processed as the background noise.

Then, when entering the background noise mode again, pr
evLsp1 and prevLsp2 are linearly interpolated to be the LSP of the current frame.

By the way, if there are enough mode bits and they can be transmitted as one mode, such processing is not necessary. Various interpolation methods other than linear interpolation are conceivable for the prevLsp1 and prevLsp2 interpolation methods.

[0126]

The speech encoding method and apparatus according to the present invention realize variable rate encoding efficiently.

Further, the speech decoding method and apparatus according to the present invention reduce background noise by using encoded data encoded by the speech encoding method and apparatus for implementing variable rate encoding. Can be generated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a mobile phone device which is an embodiment of a speech encoding method and device and a speech decoding method and device according to the present invention.

FIG. 2 is a block diagram showing a basic configuration of a speech encoding device constituting the mobile phone device.

FIG. 3 is a block diagram showing a detailed configuration of the speech encoding device shown in FIG. 2;

FIG. 4 is a block diagram illustrating a configuration of an input signal determination device that determines an input signal inside the speech encoding device.

FIG. 5 is a flowchart for explaining an algorithm of a minimum level calculation unit included in the input signal determination device shown in FIG. 4;

FIG. 6 is a characteristic diagram for explaining a reference level calculation unit included in the input signal determination device shown in FIG. 4;

FIG. 7 is a block diagram showing a basic configuration of a speech decoding device constituting the mobile phone device.

FIG. 8 is a block diagram showing a detailed configuration of the speech decoding device shown in FIG. 7;

FIG. 9 is a flowchart for explaining the operation of the speech decoding apparatus.

[Explanation of symbols]

Reference Signs List 20 audio encoding device, 21, 115 input signal determination unit, 31 audio decoding device, 240 LPC parameter reproduction control unit, 241 switching control unit, 242 index determination unit

Claims (13)

[Claims] 1. A speech encoding method for encoding an input signal consisting of a speech signal section divided into a voiced sound section or an unvoiced sound section and a background noise section at a variable rate based on a determination result of each section. An audio encoding step of dividing the input signal into predetermined encoding units on the time axis, encoding the encoded signals in each encoding unit, and outputting a plurality of types of audio encoding parameters, the audio encoding step includes: When the determination result indicates the background noise section, the plurality of types of parameters are output after a predetermined time. 2. The speech encoding method according to claim 1, wherein in the speech encoding step, the determination result of each section is always output as a basic parameter even during the predetermined time. 3. The speech encoding step includes: a short-term prediction residual calculation step for obtaining a short-term prediction residual of the input signal; and a sine wave analysis encoding step for performing sine-wave analysis encoding on the obtained short-term prediction residual. 2. A speech encoding method according to claim 1, further comprising a waveform encoding step of encoding said input signal by waveform encoding. 4. The method according to claim 3, wherein the sine wave analysis encoding step encodes the input signal when the audio signal section is voiced, and the waveform encoding step encodes the input signal when the audio signal section is unvoiced. Voice encoding method. 5. The speech encoding step according to claim 1, wherein the difference quantization is not performed in the short-term prediction residual calculating step when the background noise section is within the background noise section or one frame before is the background noise section. Item 3. The speech encoding method according to Item 3. 6. A speech coding apparatus for coding an input signal consisting of a speech signal section divided into a voiced sound section or an unvoiced sound section and a background noise section at a variable rate based on a determination result of each section. An audio encoding unit that divides an input signal into predetermined encoding units on a time axis, performs encoding in each encoding unit, and outputs a plurality of types of audio encoding parameters, wherein the audio encoding unit includes: When the determination result indicates the background noise section, the plurality of parameters are output after a predetermined time. 7. Speech coded data transmitted by coding an input signal consisting of a voice signal section divided into a voiced sound section or an unvoiced sound section and a background noise section at a variable rate based on the determination result of each section. A speech decoding method for decoding, wherein during the background noise section, the background noise is generated using a plurality of types of parameters transmitted at a predetermined time interval, and the past background noise is generated during the predetermined time interval. A speech decoding method characterized by generating the background noise using the parameters sent to the speech decoding device. 8. A short-term prediction residual calculation step for obtaining a short-term prediction residual of an input audio signal, and a sine wave analysis encoding step for performing sine-wave analysis encoding of the obtained short-term prediction residual. 8. The audio decoding method according to claim 7, wherein the audio signal is generated by an audio encoding step including a waveform encoding step of encoding the input audio signal by a waveform encoding step. 9. The audio encoded data is encoded by the sine wave analysis encoding step when the audio signal section is voiced, and is encoded by the waveform encoding step when the audio signal section is unvoiced. 9. The speech decoding method according to claim 8, wherein 10. The method according to claim 7, wherein the past parameter used to generate the background noise during the predetermined time is at least a short-term prediction coding coefficient calculated by the short-term prediction residual calculation step. Audio decoding method. 11. The background noise is generated according to a difference between a previous value of an encoded output from the waveform encoding step and a previous value of the plurality of types of parameters transmitted after the predetermined time. The speech decoding method according to claim 7, wherein 12. The speech decoding method according to claim 11, wherein an encoded output from said waveform encoding step is a gain index based on a short-term predicted encoding coefficient. 13. An audio signal section divided into a voiced sound section or an unvoiced sound section and an input signal composed of a background noise section are encoded at a variable rate based on a result of determination of each section, and transmitted speech encoded data is transmitted. A speech decoding apparatus for decoding, wherein during the background noise section, the background noise is generated using a plurality of types of parameters transmitted at a predetermined time interval, and the background noise is generated during the predetermined time interval. And a speech decoding unit for generating the background noise using the parameters sent to the speech decoding apparatus.