WO2015166693A1 - 符号化装置、復号装置、符号化方法、復号方法、符号化プログラム、復号プログラム、記録媒体 - Google Patents
符号化装置、復号装置、符号化方法、復号方法、符号化プログラム、復号プログラム、記録媒体 Download PDFInfo
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
- G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
- G10L19/02—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using spectral analysis, e.g. transform vocoders or subband vocoders
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
- G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
- G10L19/04—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using predictive techniques
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
- G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
- G10L19/04—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using predictive techniques
- G10L19/06—Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
- G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
- G10L19/04—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using predictive techniques
- G10L19/08—Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters
- G10L19/12—Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
- G10L25/00—Speech or voice analysis techniques not restricted to a single one of groups G10L15/00 - G10L21/00
- G10L25/90—Pitch determination of speech signals
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M7/00—Conversion of a code where information is represented by a given sequence or number of digits to a code where the same, similar or subset of information is represented by a different sequence or number of digits
- H03M7/30—Compression; Expansion; Suppression of unnecessary data, e.g. redundancy reduction
- H03M7/40—Conversion to or from variable length codes, e.g. Shannon-Fano code, Huffman code, Morse code
Definitions
- the present invention relates to an encoding device, a decoding device, an encoding method, a decoding method, an encoding program, a decoding program, and a recording medium that encode and decode an acoustic signal using a spectral envelope of the acoustic signal.
- Adaptive coding for orthogonal transform coefficients such as DFT (Discrete Fourier Transform) and MDCT (Modified Discrete Cosine Transform) is known as a coding method for low-bit (for example, about 10 kbit / s to 20 kbit / s) speech and acoustic signals. It has been.
- TCX transform coded excitation
- Non-Patent Document 1 a coefficient sequence X [1],..., X [N] that is a frequency domain representation of an input sound signal.
- a sequence normalized coefficient sequence X N [1],..., X N [N]
- N in [] is a positive integer.
- the amplitude spectrum envelope is calculated by the following procedure.
- Step 1 A linear prediction coefficient ⁇ 1 ,..., ⁇ P is obtained by performing linear prediction analysis on the input time domain acoustic digital signal (hereinafter referred to as input acoustic signal) in units of frames that are predetermined time intervals.
- P is a positive integer indicating the predicted order.
- Step2 linear prediction coefficient alpha 1, ..., a alpha P quantizes quantized linear prediction coefficient ⁇ alpha 1, ..., determine the ⁇ alpha P.
- the quantized linear prediction coefficients ⁇ ⁇ 1 ,..., ⁇ ⁇ P the quantized linear prediction coefficients ⁇ ⁇ 1 ,..., ⁇ ⁇ P .
- W [n] of the amplitude spectrum envelope series can be obtained by Expression (2).
- n is an integer of 1 ⁇ n ⁇ N
- exp (•) is an exponential function with the Napier number as the base
- j is an imaginary unit
- ⁇ is the amplitude of the prediction residual signal.
- a symbol written without a square bracket on the right shoulder represents a power operation. That is, ⁇ 2 represents the square of ⁇ .
- ⁇ 2 represents the square of ⁇ .
- the symbols “ ⁇ ”, “ ⁇ ”, etc. used in the sentence should be described immediately above the character that immediately follows, but are described immediately before the character due to restrictions on text notation. In the mathematical expression, these symbols are described in their original positions, that is, directly above the characters.
- Non-Patent Document 1 the “code corresponding to the spectral envelope” sent to the decoding side is the “code corresponding to the linear prediction coefficient”, and the amount of code can be small.
- the spectral envelope information obtained by the linear prediction coefficient may deteriorate the approximation accuracy in the vicinity of the peak due to the pitch period of the input acoustic signal, which causes the normalized coefficient sequence to be variable-length encoded. Encoding efficiency may be reduced.
- the present invention provides an encoding device and a decoding device that can reproduce an envelope sequence in a frequency domain with good approximation accuracy near a peak due to the pitch period of an acoustic signal with a small code amount.
- the encoding apparatus of the present invention includes a periodic integrated envelope generation unit and a variable length encoding unit.
- the periodic integrated envelope generation unit includes a spectral envelope sequence that is a frequency domain sequence corresponding to a linear prediction coefficient code obtained from an input acoustic signal in a predetermined time interval, and a frequency domain corresponding to a periodic code obtained from the input acoustic signal. And a periodic integrated envelope sequence that is a frequency domain sequence based on the period.
- the variable length encoding unit encodes a frequency domain sequence derived from the input acoustic signal on the assumption that the amplitude of the input acoustic signal is larger as the frequency of the periodic integrated envelope sequence is larger.
- the decoding device of the present invention includes a periodicity integrated envelope generation unit and a variable length decoding unit.
- the periodic integrated envelope generation unit is a periodic integrated envelope sequence that is a frequency domain sequence based on a spectrum envelope sequence that is a frequency domain sequence corresponding to a linear prediction coefficient code and a frequency domain period that corresponds to a periodic code. Is generated.
- the variable length decoding unit obtains a frequency domain sequence by decoding the variable length code on the premise that the amplitude of the acoustic signal increases as the frequency of the periodic integrated envelope sequence increases.
- encoding and decoding that can reproduce an envelope sequence in a frequency domain with good approximation accuracy near the peak due to the pitch period of the input acoustic signal with a small amount of code.
- the encoding efficiency of the acoustic signal is good.
- FIG. 6 is a diagram illustrating a functional configuration example of an encoding apparatus according to a second embodiment.
- FIG. 10 is a diagram illustrating a processing flow of the encoding apparatus according to the second embodiment.
- FIG. 6 is a diagram illustrating a functional configuration example of a decoding device according to a second embodiment.
- FIG. 10 is a diagram illustrating a processing flow of the decoding apparatus according to the second embodiment.
- FIG. 10 is a diagram illustrating a functional configuration example of an encoding apparatus according to a third embodiment.
- FIG. 10 is a diagram illustrating a processing flow of the encoding apparatus according to the third embodiment.
- FIG. 10 is a diagram illustrating a functional configuration example of a decoding device according to a third embodiment.
- FIG. 10 is a diagram illustrating a processing flow of the decoding apparatus according to the third embodiment.
- FIG. 1 shows a functional configuration example of the periodic integrated envelope sequence generation device of the present invention
- FIG. 2 shows a processing flow of the periodic integrated envelope sequence generation device of the present invention
- the periodic integrated envelope sequence generating apparatus 100 includes a spectrum envelope sequence calculating unit 120, a frequency domain converting unit 110, a periodicity analyzing unit 130, a periodic envelope sequence generating unit 140, and a periodic integrated envelope generating unit 150.
- An acoustic digital signal in the time domain is set as an input acoustic signal x (t), and a periodic integrated envelope sequence is generated by modifying the amplitude spectrum envelope sequence based on the frequency component of the coefficient sequence.
- the spectrum envelope sequence calculation unit 120 calculates the amplitude spectrum envelope sequence W [1],..., W [N] of the input acoustic signal based on the time domain linear prediction of the input acoustic signal x (t) (S120). However, N is a positive integer.
- the spectrum envelope sequence calculation unit 120 is the same as that in the prior art, and may be calculated by the following procedure.
- Step 1 Linear prediction coefficients ⁇ 1 ,..., ⁇ P are obtained by performing linear prediction analysis on the input acoustic signal in units of frames that are predetermined time intervals.
- P is a positive integer indicating the predicted order.
- the input acoustic signal x (t) at the time t becomes the past value x (t ⁇ 1),. tP) and the prediction residuals e (t) and the linear prediction coefficients alpha 1, ..., represented by the formula (1) by alpha p.
- each value W of the amplitude spectral envelope sequence [n] is the linear prediction coefficients alpha 1, ..., alpha quantized linear prediction coefficients corresponding to P ⁇ alpha 1, ..., using ⁇ alpha P Equation (2) Can be obtained.
- each value W [n] of the amplitude spectrum envelope sequence can be obtained by an equation in which ⁇ ⁇ p in Equation (2) is replaced by ⁇ p using linear prediction coefficients ⁇ 1 ,..., ⁇ P.
- the frequency domain conversion unit 110 converts the input time domain input acoustic signal into N frequency coefficient sequences X [1],..., X [N] in units of frames that are predetermined time intervals. Output (S110).
- the conversion to the frequency domain may be performed by a method such as MDCT (Modified Discrete Cosine Transform) or DFT (Discrete Fourier Transform).
- the periodicity analysis unit 130 receives the coefficient sequence X [1],..., X [N], obtains the cycle T of the coefficient sequence X [1],. S130).
- the period T is a frequency interval coefficient sequence derived from the input acoustic signal, for example, the interval between the components having periodicity of the coefficient sequence X [1],. Information).
- the period T may be expressed as the interval T, but only the difference in expression is the same.
- T is a positive value, and may be an integer or a decimal (for example, 5.0, 5.25, 5.5, 5.75).
- the periodicity analysis unit 130 may obtain and output an index S indicating the degree of periodicity by inputting the coefficient sequence X [1],..., X [N] as necessary.
- the index S is an index indicating the degree of periodicity of the frequency domain sample sequence.
- the periodicity analysis unit 130 may obtain the period T by obtaining the time domain period from the time domain input acoustic signal and converting the obtained time domain period into the frequency domain period. Alternatively, a constant multiple of a time domain period converted to a frequency domain period or a value in the vicinity thereof may be obtained as the period T. Similarly, the periodicity analysis unit 130 is an index indicating the degree of periodicity based on, for example, the magnitude of correlation between signal sequences shifted in time by the period of the time domain from the time domain input acoustic signal. S may be obtained.
- the periodic envelope sequence generation unit 140 receives the interval T and outputs a periodic envelope sequence P [1],..., P [N] (S140).
- the periodic envelope sequence P [1],..., P [N] is a discrete sequence in the frequency domain having a peak with a period due to the pitch period, that is, a discrete series corresponding to the harmonic model.
- FIG. 3 shows an example of the periodic envelope series P [1],..., P [N].
- the periodic envelope sequence P [1],..., P [N] is divided into an index that is an integer value in the vicinity of an integer multiple of the interval T and a predetermined number of indexes before and after that, as in the waveform shown in FIG.
- An index that is an integer value in the vicinity of an integer multiple of the interval T periodically has a maximum value (peak), and a value of P [n] corresponding to a predetermined number of indexes before and after the index n corresponds to the peak.
- On the horizontal axis represent discretized sample point indexes (hereinafter referred to as “frequency indexes”).
- the peak shape can be expressed by the following function Q (n), where n is a variable representing a frequency index and ⁇ is a frequency index corresponding to a maximum value (peak).
- Q the number of digits after the decimal point of the interval T is L digits
- T ′ T ⁇ 2L .
- h the height of the peak, and the peak height increases as the interval T increases.
- PD represents the width of the peak portion, and the width increases as the interval T increases.
- U is a positive integer indicating 1 to the number of peaks (for example, 1 to 10 in the case of FIG. 4), v is an integer of 1 or more (for example, about 1 to 3), and floor ( ⁇ ) is a decimal point
- the periodic envelope sequence P [n] is, for example, It is sufficient to calculate as follows. However, (U ⁇ T ′) / 2 L ⁇ v ⁇ n ⁇ (U ⁇ T ′) / 2 L + v.
- the periodic envelope series P [n] is calculated using the function Round (•) that rounds off the first decimal place and returns an integer value. You may ask as follows.
- the periodic integrated envelope generation unit 150 receives at least the periodic envelope sequences P [1],..., P [N] and the amplitude spectrum envelope sequences W [1],.
- the series W M [1],..., W M [N] is obtained (S150).
- the periodic integrated envelope W M [n] is obtained as follows. Note that ⁇ is a value determined such that the shape of the absolute value series of the periodic integrated envelope W M [n] and the coefficient X [n] is close or a predetermined value.
- the periodic integrated envelope generator 150 determines ⁇ so that the shape of the absolute value series of the periodic integrated envelope W M [n] and the coefficient X [n] is close
- the periodic integrated envelope generator 150 , coefficient sequence X [1], ..., and X [N] also input, determined ⁇ and its periodicity integrated envelope sequence W M [1] when, ..., may be output W M [N].
- ⁇ may be determined from several candidates of ⁇ , for example, two of 0.4 and 0.8, to ⁇ that minimizes E defined by the following expression. In other words, it may be determined to be ⁇ that makes the shape of the absolute value series of the periodic integrated envelope W M [n] and the coefficient X [n] close.
- ⁇ is a value that determines how much the periodic envelope P [n] is considered in the periodic integrated envelope W M [n]. In other words, ⁇ can be said to be a value that determines the mixing ratio of the amplitude spectrum envelope W [n] and the periodic envelope P [n] in the periodic integrated envelope W M [n].
- G in Equation (9) is the inner product of the absolute value sequence of each coefficient X [n] of the coefficient sequence X [1],..., X [N] and the reciprocal sequence of the periodic integrated envelope sequence.
- ⁇ W M [n] in Expression (8) is a normalized periodic integrated envelope obtained by normalizing each value W M [n] of the periodic integrated envelope with G.
- Equation (7) the fourth power of the inner product of the coefficient sequence X [1], ..., X [N] and the normalized periodic integrated envelope sequence ⁇ W M [1], ..., ⁇ W M [N] is calculated.
- This is intended to reduce the value (distance) obtained by taking the inner product by emphasizing the coefficient X [n] having a particularly large absolute value.
- ⁇ is determined so that the coefficient X [n] having a particularly large absolute value in the coefficient sequence X [1],..., X [N] is close to the periodic integrated envelope W M [n]. is doing.
- the periodicity integrated envelope generation unit 150 determines the number of candidates for ⁇ according to the degree of periodicity
- the periodicity integrated envelope generation unit 150 also receives an index S indicating the degree of periodicity as an input.
- S indicates that the frame corresponds to a high periodicity
- a ⁇ that minimizes E defined by Equation (7) is selected from a large number of candidates for ⁇
- ⁇ may be a predetermined value. That is, when determining the number of candidates for ⁇ according to the degree of periodicity in the periodicity integrated envelope generation unit 150, the higher the periodicity, the larger the number of candidates for ⁇ .
- FIG. 4 shows an example for explaining the difference between sequences generated for the same acoustic signal.
- Fig. 4 (A) shows the shape of the curve obtained by interpolating the coefficient sequence X [1], ..., X [N], and
- Fig. 4 (B) shows the periodic envelope series P [1], ..., P [N].
- 4C shows the shape of the curve obtained by interpolating the smoothed amplitude spectrum envelope sequence ⁇ W [1],..., W [N]
- FIG. 4D shows the periodic integrated envelope series. Shows the shape of the curve obtained by interpolating W M [1], ..., W M [N]. As shown in FIG.
- the periodic integrated envelope sequence W M [1],..., W M [N] is a coefficient compared to the smoothed amplitude spectrum envelope sequence ⁇ W [1],.
- the shape includes periodic peaks appearing in the rows X [1], ..., X [N].
- the periodic integrated envelope sequence W M [1],..., W M [N] has an interval T or an interval T in addition to the linear prediction coefficient or the quantized linear prediction coefficient which is information representing the spectrum envelope. And the value ⁇ can be generated.
- the peak of the amplitude due to the pitch period of the input acoustic signal can be expressed with higher accuracy than the spectral envelope determined by the linear prediction coefficient. it can. That is, the amplitude of the input acoustic signal can be estimated with high accuracy with a small amount of information of the linear prediction coefficient or the quantized linear prediction coefficient and the interval T, or the interval T and the value ⁇ .
- the smoothed amplitude spectrum envelope to W [n] is an envelope expressed by the following equation, and ⁇ is a positive constant of 1 or less for blunting (smoothing) the amplitude spectrum coefficient.
- the periodic integrated envelope sequence generation device of the present invention when used in the encoding device and the decoding device, the quantized linear obtained by a processing unit other than the periodic integrated envelope sequence generation device included in the encoding device. Since the code for specifying the prediction coefficient ⁇ ⁇ p (linear prediction coefficient code C L ) and the code for specifying the period T and the time domain period (period code C T ) are input to the decoding apparatus, the periodicity integration of the present invention If the code indicating the information of ⁇ is output from the envelope sequence generation device, the same period as the periodic integrated envelope sequence generated by the encoding-side periodic integrated envelope sequence generation device in the decoding-side periodic integrated envelope sequence generation device A gender integrated envelope sequence can be generated. Therefore, the amount of code that increases when a code is sent from the encoding device to the decoding device is small.
- the periodic integrated envelope generating unit 150 performs the amplitude spectrum envelope sequence W [1 based on the periodic components of the coefficient sequence X [1],..., X [N]. ], ..., a modification of the W [N], periodicity integrated envelope sequence W M [1], ..., that is set to W M [N] is the most important point.
- a “neighboring sample” is a sample indicated by an index that is an integer value in the vicinity of an integral multiple of the interval T.
- the “neighborhood” may be a range determined by a predetermined method such as the equations (3) to (5).
- the periodic envelope series P [1], represented by the equations (4) and (5) .., P [N] have a large value and a non-zero value in a wide range, that is, an integer multiple of the interval T (period) and many samples in the vicinity thereof. That is, the periodicity integrated envelope generation unit 150 increases the integer multiple of the interval T (period) and the values of samples in the vicinity thereof in the amplitude spectrum envelope sequence as the interval T between the components having periodicity in the coefficient sequence is wider. change.
- the periodicity integrated envelope generation unit 150 increases the amplitude spectrum envelope sequence with a wider width, that is, an integer multiple of the interval T (period) and the vicinity thereof, as the interval T of the component having periodicity in the coefficient sequence is wider. For many samples, change the sample value. “With many samples in the vicinity” means increasing the number of samples existing in a range corresponding to “neighborhood” (range determined by a predetermined method). That is, the periodic integrated envelope generation unit 150 can easily obtain the above effect by modifying the amplitude spectrum envelope sequence in this way.
- the first embodiment describes the periodic integrated envelope sequence generation device.
- Modification 1 Example of periodicity analysis using a normalized coefficient sequence
- the periodic integrated envelope sequence generation apparatus of Modification 1 is also shown in FIG.
- the processing flow of the periodic integrated envelope series generation apparatus of the modification 1 is also shown in FIG.
- the periodic integrated envelope sequence generation apparatus 101 includes a frequency domain sequence normalization unit 111, and the spectrum envelope sequence calculation unit 121 and the periodicity analysis unit 131 differ from the periodic integrated envelope sequence generation apparatus 100, and other configurations are as follows. The same. Only the differences will be described below.
- the spectrum envelope sequence calculation unit 121 obtains not only the amplitude spectrum envelope sequence W [1],..., W [N] but also the smoothed amplitude spectrum envelope sequence ⁇ W [1],.
- the spectrum envelope sequence calculation unit 121 performs the following procedure in addition to (step 1) and (step 2) indicated by the spectrum envelope sequence calculation unit 120.
- Step 3 Multiply each quantized linear prediction coefficient ⁇ ⁇ p by ⁇ p to obtain quantized smoothed linear prediction coefficients ⁇ ⁇ 1 ⁇ , ⁇ ⁇ 2 ⁇ 2 ,..., ⁇ ⁇ P ⁇ P.
- ⁇ is a positive constant of 1 or less for smoothing.
- a smoothed amplitude spectrum envelope sequence ⁇ W [1], ..., ⁇ W [N] is obtained by Expression (10) (S121).
- the spectral envelope sequence calculation unit 120 may use a linear prediction coefficient alpha p instead of quantized linear prediction coefficient ⁇ alpha p.
- Periodicity analysis unit 131 Periodicity analysis unit 131, the normalized coefficient sequence X N [1], ..., and enter the X N [N], the normalized coefficient sequence X N [1], ..., a period T of X N [N]
- the period T is obtained and output (S131). That is, in this modification, the interval between the components having the periodicity of normalized coefficient sequences X N [1],..., X N [N], which is a frequency sequence coefficient sequence derived from the input acoustic signal, is obtained as the period T.
- the periodicity analysis unit 131 may obtain and output an index S indicating the degree of periodicity by inputting the coefficient sequence X [1],..., X [N] as necessary.
- periodic integrated envelope generation unit 150 uses smoothed amplitude spectrum envelope sequences ⁇ W [instead of amplitude spectrum envelope sequences W [1], ..., W [N]. 1], ..., ⁇ W [N] may be used. In this case, the following equation is used instead of equation (6).
- a coefficient other than the periodic integrated envelope sequence generation device included in the encoding device or decoding device Sequence X [1], ..., X [N], normalized coefficient sequence XN [1], ..., XN [N], quantized linear prediction coefficient ⁇ ⁇ p , quantized smoothed linear prediction coefficient ⁇ ⁇ p ⁇ p , amplitude spectrum envelope W [1],..., W [N], smoothed amplitude spectrum envelope sequence ⁇ W [1], ..., ⁇ W [N], period T, index S, etc. are obtained. There may be.
- the periodic integrated envelope sequence generation device may be configured not to include at least one of the frequency domain conversion unit, the frequency domain normalization unit, the spectrum envelope sequence calculation unit, and the periodicity analysis unit.
- a code linear prediction coefficient code C L
- a code for specifying the period (period code C T ), a code for specifying the index S, and the like are output and input to the decoding device.
- the periodic integrated envelope sequence generation device in the encoding device receives a code (linear prediction coefficient code C L ) for specifying the quantized linear prediction coefficient ⁇ ⁇ p , the period T and the time domain. There is no need to output a code for specifying the period (periodic code C T ), a code for specifying the index S, and the like.
- the periodic integrated envelope sequence generation apparatus of the present invention when used in an encoding device or a decoding device, it is necessary to obtain the same periodic integrated envelope sequence in the encoding device and the decoding device. Therefore, it is necessary to obtain a periodic integrated envelope sequence using information that can be specified from codes output from the encoding device and input to the decoding device.
- the spectral envelope sequence calculator periodicity integrated envelope sequence generator used in the coding device calculates the amplitude spectral envelope sequence using the quantized linear prediction coefficients corresponding to the linear prediction coefficient code C L, in the decoding device
- the spectrum envelope sequence calculation unit of the periodic integrated envelope sequence generation device to be used uses the decoded linear prediction coefficient corresponding to the linear prediction coefficient code C L output from the encoding device and input to the decoding device to generate an amplitude spectrum envelope sequence. Need to ask.
- the periodic integrated envelope sequence generating device when using a periodic integrated envelope sequence in an encoding device or a decoding device, is not provided internally as described above, but a necessary requirement in the periodic integrated envelope sequence generating device is required.
- the processing unit may be provided in the encoding device and the decoding device. Such an encoding device and decoding device will be described in a second embodiment.
- FIG. 5 shows a functional configuration example of the encoding apparatus according to the second embodiment
- FIG. 6 shows a processing flow of the encoding apparatus according to the second embodiment.
- the encoding apparatus 200 includes a spectrum envelope sequence calculation unit 221, a frequency domain conversion unit 110, a frequency domain sequence normalization unit 111, a periodicity analysis unit 230, a periodic envelope sequence generation unit 140, a periodicity integrated envelope generation unit 250, a variable A long coding parameter calculation unit 260 and a variable length coding unit 270 are provided.
- Encoder 200 an audio digital signal of the input time domain as an input audio signal x (t), at least quantized linear prediction coefficient ⁇ alpha 1, ..., code C L, normalization coefficient indicating a ⁇ alpha P column X N [1], variable length ..., code C T interval T representing a cycle of X N [N], the normalized coefficient sequence X N [1], ..., and variable-length coding the X N [N]
- the code CX is output.
- the frequency domain sequence normalization unit 111 is the same as that in the first modification of the first embodiment.
- the frequency domain transform unit 110 and the periodic envelope sequence generation unit 140 are the same as those in the first embodiment. Hereinafter, different components will be described.
- the spectrum envelope sequence calculation unit 221 performs the amplitude spectrum envelope sequence W [1],..., W [N] of the input acoustic signal and the smoothed amplitude spectrum envelope sequence based on the time domain linear prediction of the input acoustic signal x (t). ⁇ W [1], ..., and calculates a ⁇ W [N], obtained in the course of calculation quantized linear prediction coefficient ⁇ ⁇ 1, ..., also obtains the code C L indicating the ⁇ ⁇ P (S221). However, N is a positive integer.
- the spectrum envelope sequence calculation unit 221 may be processed in the following procedure.
- Step 1 Linear prediction coefficients ⁇ 1 ,..., ⁇ P are obtained by performing linear prediction analysis on the input acoustic signal in units of frames that are predetermined time intervals.
- P is a positive integer indicating the predicted order.
- the input acoustic signal x (t) at the time t becomes the past value x (t ⁇ 1),. tP) and the prediction residuals e (t) and the linear prediction coefficients alpha 1, ..., represented by the formula (1) by alpha p.
- Step2 linear prediction coefficients ⁇ 1, ..., and outputs to obtain a code C L encodes the alpha P, quantized linear prediction coefficients corresponding to the code C L ⁇ ⁇ 1, ..., determine the ⁇ alpha P . Furthermore, quantized linear prediction coefficient ⁇ ⁇ 1, ..., ⁇ ⁇ using P of the input audio signals of N points amplitude spectral envelope sequence W [1], ..., determine the W [N]. For example, each value W [n] of the amplitude spectrum envelope series can be obtained by Expression (2).
- linear prediction coefficients alpha 1, ..., a method of obtaining a alpha P to be encoded code C L converts the linear prediction coefficients to LSP parameters, such as obtaining a code C L encodes the LSP parameter, linear predictive You may use any method for obtaining the code C L any convertible coefficients in the coefficient is encoded.
- Step 3 Multiply each quantized linear prediction coefficient ⁇ ⁇ p by ⁇ p to obtain quantized smoothed linear prediction coefficients ⁇ ⁇ 1 ⁇ , ⁇ ⁇ 2 ⁇ 2 ,..., ⁇ ⁇ P ⁇ P.
- ⁇ is a positive constant of 1 or less for smoothing in advance.
- the smoothed amplitude spectrum envelope sequence ⁇ W [1], ..., ⁇ W [N] is obtained by Expression (10).
- Periodicity analysis unit 230 Periodicity analysis unit 230, the normalized coefficient sequence X N [1], ..., X N as input [N], the normalized coefficient sequence X N [1], ..., X N [N] interval T ( An interval having a periodically large value is obtained, and an interval T and a code CT indicating the interval T are output (S230). Further, the periodicity analysis unit 230 also obtains and outputs an index S indicating the degree of periodicity (that is, an index indicating the degree of periodicity of the sample sequence in the frequency domain) as necessary. The period analysis section 230, if necessary, also obtained an output code C S indicating the index S. The index S and the interval T itself are the same as those of the periodicity analysis unit 131 of the first modification of the first embodiment.
- the periodic integrated envelope generation unit 250 receives at least the periodic envelope sequence P [1],..., P [N] and the amplitude spectrum envelope sequence W [1],.
- the sequence W M [1],..., W M [N] is obtained, and the periodic integrated envelope W M [n] is output.
- the integrated periodic envelope generation unit 150 selects any one of a plurality of predetermined candidate values as the value ⁇ instead of a predetermined value, the coefficient sequence X [1], ..., X [N] is also input, and a candidate value that is close to the shape of the absolute value series of periodic integrated envelope W M [n] and coefficient X [n] among a plurality of predetermined candidate values is obtained as value ⁇ .
- the code C ⁇ indicating the value ⁇ is also output (S250).
- the periodic integrated envelope W M [n] and the value ⁇ are the same as those in the first embodiment, and the periodic integrated envelope W M [n] may be obtained as in the equations (6),.
- the periodicity integrated envelope generation unit 150 determines the number of candidates for ⁇ according to the degree of periodicity, the periodicity integrated envelope generation unit 150 also receives an index S indicating the degree of periodicity, and the index S is In the case of a frame corresponding to high periodicity, ⁇ that minimizes E defined by Equation (7) is selected from among a large number of candidate ⁇ , and the index S is low in periodicity.
- ⁇ may be set to one predetermined value. When ⁇ is set to a predetermined value, it is not necessary to output the code C ⁇ indicating the value ⁇ .
- variable length coding parameter calculation unit 260 performs regular integration with the periodic integrated envelope sequence W M [1],..., W M [N] and the smoothed amplitude spectrum envelope sequence ⁇ W [1],. reduction coefficient sequence X n [1], ..., and enter the X n [n], obtaining the variable length coding parameters r n (S260).
- Variable-length encoding parameter calculating unit 260 periodicity integrated envelope sequence W M [1], ..., characterized in that in dependence on the amplitude value obtained from W M [N] to calculate the variable length coding parameters r n It is said.
- the variable length coding parameter is a parameter that specifies a possible range of the amplitude of each coefficient of the signal to be coded, that is, the normalized coefficient sequence X N [1],..., X N [N].
- the Rice parameter corresponds to a variable length coding parameter
- the range that the amplitude of a signal to be coded can take corresponds to the variable length coding parameter.
- variable length coding parameter calculating unit 260 for each normalization moiety coefficient sequence which is part of the normalization coefficient sequence, to calculate the variable length coding parameters r n.
- the normalized partial coefficient sequences include the coefficients of the normalized coefficient sequence without overlapping.
- Step1 normalized coefficient sequence X N [1], ..., X N the logarithm of the average of the amplitudes of the coefficients of [N], serving as a reference Rice parameter sb equation as (variable length coding parameter as a reference) Calculate as follows.
- the sb is encoded only once for each frame, and transmitted to the decoding apparatus 400 as a code C sb corresponding to the reference Rice parameter (reference variable-length encoding parameter).
- the average value of the amplitudes of the normalized coefficient sequences X N [1],..., X N [N] can be estimated from other information transmitted to the decoding apparatus 400, the encoding apparatus 200 and the decoding apparatus 400 are common.
- a method of approximately determining sb from the estimated value of the average amplitude value may be determined.
- the average value of the amplitude can be estimated from other information transmitted to the decoding device 400. In this case, it is not necessary to encode sb and output the code C sb corresponding to the reference rice parameter to the decoding device 400.
- Step 2 The threshold value ⁇ is calculated by the following equation. ⁇ is the logarithm of the average amplitude of values obtained by dividing each value W M [n] of the periodic integrated envelope sequence by each value ⁇ W [n] of the smoothed amplitude spectrum envelope sequence.
- Step3 W M [n ] / ⁇ W [n]
- Variable length coding unit 270 the normalization coefficients using variable length coding parameters r n obtained by the variable length coding parameter calculating section 260 columns X N [1], ..., variable-length codes X N [N]
- the variable length code C X is output (S270).
- the variable length coding unit 270, the normalized coefficient sequence X N [1] using a Rice parameter r n obtained by the variable length coding parameter calculating section 260, ..., and Rice coding the X N [N] The obtained code is output as a variable length code CX .
- Rice parameter r n obtained by the variable length coding parameter calculation unit 260, a variable length coding parameter dependent on the amplitude value of the periodicity integration envelope sequence, a larger value as the frequency value greater periodicity integrated envelope sequence It has become.
- Rice coding is one of the known techniques of variable-length coding which depends on the amplitude value, and performs variable length coding which depends on the amplitude value using the Rice parameter r n.
- the periodic integrated envelope sequence generated by the periodic integrated envelope generating unit 250 expresses the spectral envelope of the input acoustic signal with high accuracy.
- variable length coding unit 270 determines that the frequency of the coefficient sequence in the frequency domain of the input acoustic signal X [1],..., X [N] increases as the frequency of the periodic integrated envelope sequence increases. Therefore, the normalized coefficient sequence X N [1], ..., X N [N] is variable-length encoded, in other words, depends on the amplitude value using the variable-length encoding parameter.
- the normalized coefficient sequence X N [1],..., X N [N] is encoded by variable length coding.
- the amplitude value here is an average amplitude value of the coefficient sequence to be encoded, an estimated value of the amplitude of each coefficient included in the coefficient sequence, an estimated value of an envelope of the amplitude of the coefficient sequence, or the like.
- the encoding apparatus 200 includes a code C L indicating the quantized linear prediction coefficients ⁇ ⁇ 1 ,..., ⁇ ⁇ P obtained by such processing, a code C T indicating the interval T, and a normalized coefficient sequence X N [ 1],..., X N [N]
- a variable length code C X obtained by variable length encoding is output.
- code C sb showing a variable length coding parameter sb as a code C [delta] and the reference indicating the value [delta], if necessary.
- the code output from the encoding device 200 is input to the decoding device 400.
- the encoding device includes only the periodic envelope sequence generation unit 140, the periodic integrated envelope generation unit 250, the variable length encoding parameter calculation unit 260, and the variable length encoding unit 270, and is generated outside the encoding device. Smoothed amplitude spectrum envelope sequence ⁇ W [1], ..., ⁇ W [N], normalized coefficient sequence XN [1], ..., XN [N], interval T, and amplitude as necessary The spectrum envelope sequence W [1],..., W [N] and the index S as necessary may be input and the variable length code C X may be output.
- FIG. 7 shows a functional configuration example of the decoding apparatus according to the second embodiment
- FIG. 8 shows a processing flow of the decoding apparatus according to the second embodiment.
- Decoding apparatus 400 includes spectrum envelope sequence calculation unit 421, periodic envelope sequence generation unit 440, periodic integrated envelope generation unit 450, variable length coding parameter calculation unit 460, variable length decoding unit 470, frequency domain sequence denormalization unit 411 and a frequency domain inverse transform unit 410.
- Decoding device 400 quantized linear prediction coefficient ⁇ ⁇ 1, ..., ⁇ ⁇ code indicating the P C L, code C T indicating the interval T, the normalization coefficient sequence X N [1], ..., X N [N ] to receive the variable length code C X which variable length coding, and outputs an acoustic signal.
- code C S indicating the sign C sb and index S indicating a variable-length coding parameters sb as a code C [delta] and the reference indicating the value [delta], if necessary. Details of each component will be described below.
- Spectrum envelope series calculation unit 421 inputs the code C L, the amplitude spectral envelope sequence W [1], ..., W [N] and the smoothed amplitude spectrum envelope sequence ⁇ W [1], ..., ⁇ W [N] Is calculated (S421). More specifically, the processing may be performed according to the following procedure.
- Step1 decodes the code C L, decodes the linear prediction coefficient ⁇ ⁇ 1, ..., obtaining ⁇ alpha P.
- Step2 decoded linear prediction coefficient ⁇ ⁇ 1, ..., ⁇ amplitude spectral envelope sequence W of N points using ⁇ P [1], ..., determine the W [N].
- each value W [n] of the amplitude spectrum envelope series can be obtained by Expression (2).
- Step 3 Each of the decoded linear prediction coefficients ⁇ ⁇ p is multiplied by ⁇ p to obtain decoded smoothed linear prediction coefficients ⁇ ⁇ 1 ⁇ , ⁇ ⁇ 2 ⁇ 2 ,..., ⁇ ⁇ P ⁇ P.
- ⁇ is a positive constant of 1 or less for smoothing in advance.
- the smoothed amplitude spectrum envelope sequence ⁇ W [1], ..., ⁇ W [N] is obtained by Expression (10).
- Periodicity envelope sequence generating unit 440 inputs the code C T indicating the interval T, and decodes the code C T, obtaining a spacing T. Then, periodic envelope sequences P [1],..., P [N] are obtained and output by the same method as the periodic envelope sequence generation unit 140 of the encoding device 200 (S440).
- Periodicity integrated envelope generator 450 decodes the code C [delta], to obtain a value [delta]. However, if the code C [delta] is not input, the decoding of the code C [delta] is not performed, to obtain a pre-stored value [delta] Periodicity integrated envelope generator 450.
- the periodic integrated envelope generation unit 450 acquires the index S by decoding the code C S , and the acquired index S is a frame corresponding to the high periodicity. In the case of, the code C ⁇ is decoded to obtain the value ⁇ . If the obtained index S is a frame corresponding to low periodicity, the code C ⁇ is not decoded, and the periodic integrated envelope is obtained. The value ⁇ stored in advance in the generation unit 450 is acquired. Then, the periodic integrated envelope generation unit 450 obtains the periodic integrated envelope sequence W M [1],..., W M [N] by Expression (6). (S450)
- variable length coding parameter calculation unit 460 encodes the periodic integrated envelope sequence W M [1],..., W M [N] and the smoothed amplitude spectrum envelope sequence ⁇ W [1],. as input C sb, to obtain a variable length coding parameters r n (S460).
- a method of approximately determining sb from the estimated average amplitude value estimated from the other information is determined. Also good. In this case, the code C sb is not input.
- a variable length coding parameter calculation method will be described by taking as an example the case of performing rice decoding for each sample.
- Step 1 The code C sb is decoded to obtain a reference rice parameter sb (a reference variable-length encoding parameter).
- a reference rice parameter sb a reference variable-length encoding parameter
- Step 2 The threshold value ⁇ is calculated by the equation (14).
- Step3 W M [n ] / ⁇ W [n]
- variable length decoding unit 470 obtains variable length coding parameters r n by decoding the variable length codes C X using the decoded normalization coefficient sequence ⁇ X N [1], ... , ⁇ X N [N] is obtained (S470).
- the variable length decoding unit 470, a variable length coding parameter calculating section 460 obtains the Rice parameter r n by decoding the variable length codes C X using the decoded normalization coefficient sequence ⁇ X N [1], ... , Get ⁇ X N [N].
- the decoding method of the variable length decoding unit 470 corresponds to the encoding method of the variable length encoding unit 270.
- the frequency domain sequence inverse normalization unit 411 performs the decoding normalization coefficient sequence ⁇ X N [1],..., ⁇ X N [N] and the smoothed amplitude spectrum envelope sequence ⁇ W [1], ..., ⁇ W [N].
- ⁇ X [n] ⁇ X N [n] ⁇ ⁇ W [n]
- the decoding coefficient sequence ⁇ X [1],..., ⁇ X [N] is obtained and output (S411).
- the frequency domain inverse transform unit 410 receives the decoded coefficient sequence ⁇ X [1],..., ⁇ X [N] as input, and outputs the decoded coefficient sequence ⁇ X [1], ..., ⁇ X [N] in a predetermined time interval.
- the sound signal is converted into a certain frame unit (time domain) (S410).
- the decoding apparatus includes only a periodic envelope sequence generation unit 440, a periodic integrated envelope generation unit 450, a variable length coding parameter calculation unit 460, and a variable length decoding unit 470, and is input to the decoding apparatus as necessary.
- the smoothed amplitude spectrum envelope sequence ⁇ W [1], ..., W [N] the smoothed amplitude spectrum envelope sequence ⁇ W [1], ..., W [N]
- the amplitude spectrum envelope series W [1] obtained outside the decoding apparatus.
- variable-length coding is a coding method that improves coding efficiency by adaptively determining a code in accordance with a possible range of the amplitude of an input value to be coded.
- normalized coefficient sequences X N [1],..., X N [N] that are frequency sequence coefficient sequences are to be encoded, but the amplitude of each coefficient included in the coefficient sequence to be encoded is If variable-length coding is performed using variable-length coding parameters obtained using information more accurately, the coding efficiency of the variable-length coding itself performed by the coding apparatus is increased.
- the decoding device in order for the decoding device to obtain the variable-length encoding parameter, it is necessary to send more accurately the amplitude information of each coefficient included in the coefficient sequence to be encoded from the encoding device to the decoding device. Therefore, the amount of code sent from the encoding device to the decoding device increases.
- a method for obtaining an estimated value of the amplitude of each coefficient included in the coefficient sequence to be encoded from a code with a small code amount is required. Since the periodic integrated envelope sequence W M [1],..., W M [N] of the second embodiment approximates the coefficient sequence X [1],..., X [N] with high accuracy,
- the envelope including the peak of the amplitude due to the pitch period of the input acoustic signal input to the encoding device is expressed by the code C L , the code C T , and the code C. It can be reproduced by a decoding device with a small amount of information of only ⁇ .
- the encoding device and the decoding device of the second embodiment are often used in combination with an encoding device and a decoding device that perform encoding and decoding with linear prediction and pitch prediction.
- the code C L and the code C T are decoded from a coding apparatus that performs coding with linear prediction and pitch prediction outside the coding apparatus 200, and with linear prediction and pitch prediction outside the decoding apparatus 400. It is the code
- C ⁇ .
- the code amount of the code C ⁇ is small (each is about 3 bits at most, and an effect can be obtained even with 1 bit), and corresponds to the variable length coding parameter for each partial sequence included in the normalized coefficient sequence to be coded. Less than the total code amount of codes.
- the encoding efficiency can be improved with a small increase in the code amount.
- the encoding apparatus 200 includes: A frequency domain based on a spectrum envelope sequence that is a frequency domain sequence corresponding to a linear prediction coefficient code obtained from an input acoustic signal in a predetermined time interval and a frequency domain period corresponding to a periodic code obtained from the input acoustic signal Periodic integrated envelope generator 250 for generating a periodic integrated envelope sequence that is a sequence of A variable length encoding unit 270 that encodes a frequency domain sequence derived from an input acoustic signal on the assumption that the amplitude of the input acoustic signal is larger as the frequency of the periodic integrated envelope sequence is larger.
- the decoding device 400 has A periodic integrated envelope that generates a periodic integrated envelope sequence that is a frequency domain sequence based on a spectrum envelope sequence that is a frequency domain sequence corresponding to a linear prediction coefficient code and a frequency domain period that corresponds to a periodic code.
- Generation unit 450 A variable length decoding unit 470 that decodes a variable length code to obtain a frequency domain sequence on the premise that the amplitude of the acoustic signal is larger as the frequency of the periodic integrated envelope sequence is larger, What is necessary is just to make it have.
- “derived from the input sound signal” means being obtained from the input sound signal or corresponding to the input sound signal. For example, the coefficient sequence X [1],..., X [N] and the normalized coefficient sequence X N [1],..., X N [N] are frequency domain sequences derived from the input acoustic signal.
- FIG. 9 shows a functional configuration example of the encoding apparatus of the third embodiment
- FIG. 10 shows a processing flow of the encoding apparatus of the third embodiment.
- the encoding apparatus 300 includes a spectral envelope sequence calculation unit 221, a frequency domain conversion unit 110, a frequency domain sequence normalization unit 111, a periodicity analysis unit 330, a periodicity envelope sequence generation unit 140, a periodicity integrated envelope generation unit 250, a variable A long coding parameter calculation unit 260, a second variable length coding parameter calculation unit 380, and a variable length coding unit 370 are provided.
- Encoding apparatus 300 a sound digital signal of the input time domain as an input audio signal x (t), at least quantized linear prediction coefficient ⁇ alpha 1, ..., code C L, normalization coefficient indicating a ⁇ alpha P , X N [1],..., X N [N] representing the period of the code C T , coefficient sequence X [1],..., X [N] or normalized coefficient sequence X N [1],. , X N code C S indicating the predetermined index S and the index S indicating the degree of periodicity of the [N], the normalized coefficient sequence X N [1], variable that ... and variable-length coding the X N [N]
- the long code CX is output.
- the frequency domain sequence normalization unit 111 is the same as that in the first modification of the first embodiment.
- the frequency domain transform unit 110 and the periodic envelope sequence generation unit 140 are the same as those in the first embodiment.
- the amplitude spectrum envelope sequence calculation unit 221, the periodic integrated envelope generation unit 250, and the variable length coding parameter calculation unit 260 are the same as those in the second embodiment.
- different components will be described.
- the periodicity analysis unit 330 receives the normalization coefficient sequence X N [1],..., X N [N] as inputs, An index S indicating the degree of periodicity of the normalization coefficient sequence X N [1],..., X N [N] and an interval T (interval that periodically becomes a large value) are obtained. and it outputs the code C T showing the codes C S and interval T and spacing T shown (S330).
- the index S and the interval T itself are the same as those of the periodicity analysis unit 131 of the first modification of the first embodiment.
- variable-length coding parameter calculation unit 260 calculates the variable length coding parameters r n, the index S If it is not in the range that indicates that a large degree of predetermined periodicity, the second variable length coding parameter calculation unit 380 calculates the variable length coding parameters r n (S390).
- the “range indicating that the predetermined degree of periodicity is large” may be set, for example, when the index S is equal to or greater than a predetermined threshold.
- the second variable length coding parameter calculation unit 380 normalizes the amplitude spectrum envelope sequence W [1], ..., W [N] and the smoothed amplitude spectrum envelope sequence ⁇ W [1], ..., ⁇ W [N]. coefficient sequence X n [1], ..., and enter the X n [n], obtaining the variable length coding parameters r n (S380).
- Variable-length encoding parameter calculating unit 260 periodicity integrated envelope sequence W M [1], ..., characterized in that in dependence on the amplitude value obtained from W M [N] to calculate the variable length coding parameters r n
- the second variable length coding parameter calculation unit 380 is characterized in that the variable length coding parameter is calculated depending on the amplitude value obtained from the amplitude spectrum envelope sequence.
- a variable length coding parameter calculation method will be described by taking as an example the case of performing rice coding for each sample.
- Step 1 The logarithm of the average amplitude of each coefficient of the normalized coefficient sequence X N [1],..., X N [N] is expressed as a reference Rice parameter sb (reference variable-length encoding parameter). 13). This process is the same as that of the variable length coding parameter calculation unit 260.
- Step 2 The threshold value ⁇ is calculated by the following equation. ⁇ is the logarithm of the average amplitude of values obtained by dividing each value W [n] of the amplitude spectrum envelope series by each value of the smoothed amplitude spectrum envelope series to W [n].
- Step3 W [n] / ⁇ W [n]
- Variable length coding unit 370 by using the variable length coding parameters r n normalized coefficient sequence X N [1], ..., the X N [N] and variable length coding, and outputs a variable-length code C X ( S370).
- variable length coding parameters r n if the range indicates that the degree of periodicity indicator S is predetermined large, a variable length coding parameters r n of the variable length coding parameter calculation unit 260 has calculated There, if the index S is not in the range that indicates that the degree of a predetermined periodicity greater, a variable length coding parameters r n the second variable length coding parameter calculation unit 380 has calculated.
- the encoding apparatus 300 includes a code C L indicating quantized linear prediction coefficients ⁇ ⁇ 1 ,..., ⁇ ⁇ P obtained by such processing, a code C S indicating an index S indicating the degree of periodicity, and an interval.
- a variable length code C X obtained by variable length coding the code C T indicating the T and the normalized coefficient sequence X N [1],..., X N [N] is output and transmitted to the decoding side.
- output code C sb showing a variable length coding parameters sb as a code C [delta] and the reference indicating the value [delta], if necessary, sent to the decoding side.
- the encoding apparatus includes a periodic envelope sequence generation unit 140, a periodic integrated envelope generation unit 250, a variable length encoding parameter calculation unit 260, a second variable length encoding parameter calculation unit 380, and a variable length encoding unit 370. And a smoothed amplitude spectrum envelope sequence ⁇ W [1], ..., ⁇ W [N] and a normalized coefficient sequence X N [1], ..., X N [N] generated outside the encoder ., W [N] as necessary, and an index S as necessary, and a variable length code C X may be output.
- FIG. 11 shows a functional configuration example of the decoding apparatus according to the third embodiment
- FIG. 12 shows a processing flow of the decoding apparatus according to the third embodiment.
- the decoding apparatus 500 includes a spectrum envelope sequence calculation unit 421, an index decoding unit 530, a periodic envelope sequence generation unit 440, a periodic integrated envelope generation unit 450, a variable length coding parameter calculation unit 460, and a second variable length coding parameter calculation. 580, variable length decoding section 570, frequency domain sequence inverse normalization section 411, and frequency domain inverse transform section 410.
- Decoding device 500 quantized linear prediction coefficient ⁇ alpha 1, ..., ⁇ code C L indicating the alpha P, code C S indicating the index S, code C T, normalized coefficient sequence X N [1 showing the interval T ],..., X N [N] variable length code C X is received, and an acoustic signal is output. Even receive code C sb showing a variable length coding parameters sb as a code C [delta] and the reference indicating the value [delta], if necessary.
- the spectrum envelope sequence calculation unit 421, the periodic envelope sequence generation unit 440, the periodic integrated envelope generation unit 450, the variable length coding parameter calculation unit 460, the frequency domain sequence denormalization unit 411, and the frequency domain inverse conversion unit 410 are examples. Same as 2. Hereinafter, different components will be described.
- Index decoding unit 530 decodes the code C S, to obtain an index S.
- the decoding device 500 in the case of a range indicating that the degree of periodicity indicator S is predetermined large, variable-length coding parameter calculation unit 460 calculates the variable length coding parameters r n, defined index S in advance If the degree of periodicity is not the range indicated is greater, the second variable length coding parameter calculation unit 580 calculates the variable length coding parameters r n (S590).
- the “range indicating that the predetermined degree of periodicity is large” is the same range as that of the encoding apparatus 300.
- the second variable length coding parameter calculation unit 580 includes the amplitude spectrum envelope sequence W [1],..., W [N] and the smoothed amplitude spectrum envelope sequence ⁇ W [1],. as input sb, obtaining a variable length coding parameters r n (S580).
- a method of approximately determining sb from the estimated average amplitude value estimated from the other information is determined. Also good. In this case, the code C sb is not input.
- a variable length coding parameter calculation method will be described by taking as an example the case of performing rice decoding for each sample.
- Step 1 The code C sb is decoded to obtain a reference rice parameter sb (a reference variable-length encoding parameter).
- a reference rice parameter sb a reference variable-length encoding parameter
- Step 2 The threshold value ⁇ is calculated by the equation (16).
- Step3 W [n] / ⁇ W [n]
- Variable length decoding unit 570 by using the variable length coding parameters r n variable length code C X decrypted by the decryption normalized coefficient sequence ⁇ X N [1], ... , ⁇ X N Request [N] (S570 ).
- variable length coding parameters r n if the range indicates that the degree of periodicity indicator S is predetermined large, a variable length coding parameters r n of the variable length coding parameter calculation unit 460 has calculated There, if the index S is not in the range that indicates that the degree of a predetermined periodicity greater, a variable length coding parameters r n the second variable length coding parameter calculation unit 580 has calculated.
- Modification 1 of Decoding Device (Example in which information is input from the outside)
- the periodic envelope sequence generation unit 440 the periodic integrated envelope generation unit 450, the variable length coding parameter calculation unit 460, the second variable length coding parameter calculation unit 580, and the variable length decoding unit 570 are included.
- the smoothed amplitude spectrum envelope sequence ⁇ W [1], ..., ⁇ W [N] obtained outside the decoding apparatus Amplitude spectrum envelope series W [1], ..., W [N], interval T, index S are also input, and normalization coefficient sequence X N [1], ..., X N [N] is output and smoothed externally.
- the time domain acoustic signal may be converted by multiplying the normalized amplitude spectrum envelope sequence.
- the encoding device and the decoding device obtain a variable length encoding parameter using the periodic integrated envelope sequence when the degree of periodicity of the acoustic signal to be encoded is large, and perform encoding. If the degree of periodicity of the target acoustic signal is not large, the variable length coding parameter is obtained using the amplitude spectrum envelope sequence, so that the variable length coding parameter can be used for variable length coding. There is an effect that the encoding accuracy can be increased.
- a power sequence, , W [n], ⁇ W [n], W M [n] may be a power spectrum envelope sequence, a smoothed power spectrum envelope sequence, or a periodic integrated envelope sequence that is a power sequence.
- the program describing the processing contents can be recorded on a computer-readable recording medium.
- a computer-readable recording medium any recording medium such as a magnetic recording device, an optical disk, a magneto-optical recording medium, and a semiconductor memory may be used.
- this program is distributed by selling, transferring, or lending a portable recording medium such as a DVD or CD-ROM in which the program is recorded. Furthermore, the program may be distributed by storing the program in a storage device of the server computer and transferring the program from the server computer to another computer via a network.
- a computer that executes such a program first stores a program recorded on a portable recording medium or a program transferred from a server computer in its own storage device.
- the computer reads a program stored in its own recording medium and executes a process according to the read program.
- the computer may directly read the program from a portable recording medium and execute processing according to the program, and the program is transferred from the server computer to the computer.
- the processing according to the received program may be executed sequentially.
- the program is not transferred from the server computer to the computer, and the above-described processing is executed by a so-called ASP (Application Service Provider) type service that realizes a processing function only by an execution instruction and result acquisition. It is good.
- the program in this embodiment includes information that is used for processing by an electronic computer and that conforms to the program (data that is not a direct command to the computer but has a property that defines the processing of the computer).
- the present apparatus is configured by executing a predetermined program on a computer.
- a predetermined program on a computer.
- at least a part of these processing contents may be realized by hardware.
- Periodic integrated envelope sequence generation device 110 Frequency domain conversion unit 111 Frequency domain coefficient normalization unit 120, 121, 221, 421 Spectral envelope sequence calculation unit 130, 131, 230, 330 Periodicity analysis unit 140, 440 Periodicity Envelope sequence generation unit 150, 250, 450 Periodic integrated envelope generation unit 200, 300 Encoding device 260, 360, 460 Variable length encoding parameter calculation unit 270, 370 Variable length encoding unit 380, 580 Second variable length encoding Parameter calculation unit 400, 500 decoding device 410 frequency domain inverse transformation unit 411 frequency domain sequence inverse normalization unit 470, 570 variable length decoding unit 530 index decoding unit
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Abstract
Description
(step1)所定の時間区間であるフレーム単位で、入力された時間領域の音響ディジタル信号(以下、入力音響信号)に対する線形予測分析を行って線形予測係数α1,…,αPを求める。ただし、Pは予測次数を示す正整数である。例えば、全極型モデルであるP次自己回帰過程により、時刻tでの入力音響信号x(t)は、P時点まで遡った過去の自分自身の値x(t-1),…,x(t-P)と予測残差e(t)と線形予測係数α1,…,αpによって式(1)で表される。
x(t)=α1x(t-1)+…+αp x(t-P)+e(t) (1)
スペクトル包絡系列計算部120は、入力音響信号x(t)の時間領域の線形予測に基づき、入力音響信号の振幅スペクトル包絡系列W[1],…,W[N]を計算する(S120)。ただし、Nは正整数である。スペクトル包絡系列計算部120は、従来技術と同じであり、以下の手順で計算すればよい。
周波数領域変換部110は、所定の時間区間であるフレーム単位で、入力された時間領域の入力音響信号を周波数領域のN点の係数列X[1],…,X[N]に変換して出力する(S110)。周波数領域への変換は、MDCT(変形離散コサイン変換)やDFT(離散フーリエ変換)などの方法で行えばよい。
周期性分析部130は、係数列X[1],…,X[N]を入力とし、当該係数列X[1],…,X[N]の周期Tを求め、周期Tを出力する(S130)。
周期性包絡系列生成部140は、間隔Tを入力とし、周期性包絡系列P[1],…,P[N]を出力する(S140)。周期性包絡系列P[1],…,P[N]は、ピッチ周期に起因する周期でピークを持つ周波数領域の離散系列、すなわち調波モデルに対応する離散系列である。図3に周期性包絡系列P[1],…,P[N]の例を示す。周期性包絡系列P[1],…,P[N]は、図3に示された波形のように、間隔Tの整数倍の近傍の整数値であるインデックスと、その前後所定数のインデックスに対応する周期性包絡の値のみ正の値を持ち、それ以外は0であるような系列である。間隔Tの整数倍の近傍の整数値であるインデックスが周期的に最大値(ピーク)をとり、その前後所定数のインデックスに対応するP[n]の値は、そのインデックスnがピークに対応するインデックスから離れるにつれて単調減少する関係にある。図3の横軸の1,2,…,は離散化サンプル点のインデックス(以下、「周波数インデックス」)を表す。
周期性統合包絡生成部150は、少なくとも、周期性包絡系列P[1],…,P[N]、振幅スペクトル包絡系列W[1],…,W[N]を入力とし、周期性統合包絡系列WM[1],…,WM[N]を求める(S150)。具体的には、周期性統合包絡WM[n]を次式のように求める。
図4に同じ音響信号に対して生成された系列の違いを説明するための例を示す。図4(A)に係数列X[1],…,X[N]を補間した曲線の形状を、図4(B)に周期性包絡系列P[1],…,P[N]を補間した曲線の形状を、図4(C)に平滑化振幅スペクトル包絡系列~W[1],…,~W[N]を補間した曲線の形状を、図4(D)に周期性統合包絡系列WM[1],…,WM[N]を補間した曲線の形状を示す。図4に示すとおり、周期性統合包絡系列WM[1],…,WM[N]は、平滑化振幅スペクトル包絡系列~W[1],…,~W[N]に比べて、係数列X[1],…,X[N]に現れる周期的なピークを含んだ形状となっている。また、周期性統合包絡系列WM[1],…,WM[N]は、スペクトル包絡を表す情報である線形予測係数または量子化済線形予測係数の他に、間隔T、または、間隔Tと値δの情報があれば生成できる。したがって、入力音響信号のスペクトル包絡を表す情報に少ない情報量を追加するだけで、入力音響信号のピッチ周期に起因する振幅のピークを、線形予測係数により求まるスペクトル包絡より高精度に表現することができる。すなわち、線形予測係数または量子化済線形予測係数と、間隔T、または、間隔Tと値δと、の少ない情報量で入力音響信号の振幅を高精度に推定することができることになる。なお、平滑化振幅スペクトル包絡~W[n]は次式で表現される包絡であり、γは振幅スペクトル係数を鈍らせる(平滑化する)ための1以下の正の定数である。
実施例1の周期性統合包絡系列生成装置100では、周期性統合包絡生成部150が係数列X[1],…,X[N]の周期性成分に基づいて、振幅スペクトル包絡系列W[1],…,W[N]を変形し、周期性統合包絡系列WM[1],…,WM[N]としている点が最も重要なポイントである。特に、係数列X[1],…,X[N]の周期性の程度が大きいほど、すなわち、周期性を有する成分の大きさが大きいほど、振幅スペクトル包絡系列W[1],…,W[N]のうち間隔T(周期)の整数倍およびそれらの近傍のサンプルの値を大きく変更すれば、上記の効果を得やすい。「近傍のサンプル」とは、間隔Tの整数倍の近傍の整数値であるインデックスで示されるサンプルである。また、「近傍」とは、例えば、式(3)~(5)などのあらかじめ定めた方法で決まる範囲とすればよい。
変形例1の周期性統合包絡系列生成装置も図1に示す。また、変形例1の周期性統合包絡系列生成装置の処理フローも図2に示す。周期性統合包絡系列生成装置101は、周波数領域系列正規化部111も備える点と、スペクトル包絡系列計算部121、周期性分析部131が周期性統合包絡系列生成装置100と異なり、その他の構成は同じである。以下では相違点についてのみ説明する。
スペクトル包絡系列計算部121は、振幅スペクトル包絡系列W[1],…,W[N]だけではなく、平滑化振幅スペクトル包絡系列~W[1],…,~W[N]も求める。
周波数領域系列正規化部111は、係数列X[1],…,X[N]の各係数を平滑化振幅スペクトル包絡系列~W[1],…,~W[N]の各係数で除算して正規化係数列XN[1],…,XN[N]を得る。すなわち、n=1,…,Nに対して
XN[n]=X[n]/~W[n] (11)
の計算を行い、正規化係数列XN[1],…,XN[N]を求める(S111)。
周期性分析部131は、正規化係数列XN[1],…,XN[N]を入力とし、当該正規化係数列XN[1],…,XN[N]の周期Tを求め、周期Tを出力する(S131)。すなわち、本変形例では、入力音響信号に由来する周波数領域の係数列である正規化係数列XN[1],…,XN[N]の周期性を有する成分の間隔を周期Tとして求める。また、周期性分析部131は、必要に応じて、係数列X[1],…,X[N]を入力とし、周期性の程度を示す指標Sも求めて出力してもよい。
本発明の周期性統合包絡系列生成装置を符号化装置や復号装置が内部に備えている場合には、符号化装置や復号装置に含まれる周期性統合包絡系列生成装置以外の処理部で、係数列X[1],…,X[N]、正規化係数列XN[1],…,XN[N]、量子化済線形予測係数^αp、量子化済平滑化線形予測係数^αpγp、振幅スペクトル包絡W[1],…,W[N]、平滑化振幅スペクトル包絡系列~W[1],…,~W[N]、周期T、指標Sなどが求められていることがある。このような場合は、周期性統合包絡系列生成装置に、周波数領域変換部、周波数領域正規化部、スペクトル包絡系列計算部、周期性分析部の少なくとも何れかを備えない構成としてもよい。この場合には、符号化装置内の周期性統合包絡系列生成装置以外の処理部から、量子化済線形予測係数^αpを特定する符号(線形予測係数符号CL)、周期Tや時間領域の周期を特定する符号(周期符号CT)、指標Sを特定する符号、などが出力され、復号装置に入力される。したがって、この場合には、符号化装置内の周期性統合包絡系列生成装置からは、量子化済線形予測係数^αpを特定する符号(線形予測係数符号CL)、周期Tや時間領域の周期を特定する符号(周期符号CT)、指標Sを特定する符号、などを出力する必要がない。
図5に実施例2の符号化装置の機能構成例を、図6に実施例2の符号化装置の処理フローを示す。符号化装置200は、スペクトル包絡系列計算部221、周波数領域変換部110、周波数領域系列正規化部111、周期性分析部230、周期性包絡系列生成部140、周期性統合包絡生成部250、可変長符号化パラメータ計算部260、可変長符号化部270を備える。符号化装置200は、入力された時間領域の音響ディジタル信号を入力音響信号x(t)とし、少なくとも量子化済線形予測係数^α1,…,^αPを示す符号CL、正規化係数列XN[1],…,XN[N]の周期を表す間隔Tの符号CT、正規化係数列XN[1],…,XN[N]を可変長符号化した可変長符号CXを出力する。周波数領域系列正規化部111は実施例1変形例1と同じである。周波数領域変換部110と周期性包絡系列生成部140は実施例1と同じである。以下では異なる構成部について説明する。
スペクトル包絡系列計算部221は、入力音響信号x(t)の時間領域の線形予測に基づき、入力音響信号の振幅スペクトル包絡系列W[1],…,W[N]と平滑化振幅スペクトル包絡系列~W[1],…,~W[N]を計算し、計算の過程で得た量子化済線形予測係数^α1,…,^αPを示す符号CLも求める(S221)。ただし、Nは正整数である。スペクトル包絡系列計算部221は、以下の手順で処理すればよい。
周期性分析部230は、正規化係数列XN[1],…,XN[N]を入力とし、当該正規化係数列XN[1],…,XN[N]の間隔T(周期的に大きな値となる間隔)を求め、間隔Tと間隔Tを示す符号CTを出力する(S230)。また、周期性分析部230は、必要に応じて、周期性の程度を示す指標S(すなわち、周波数領域のサンプル列の周期性の程度を示す指標)、も求めて出力する。また、周期性分析部230は、必要に応じて、指標Sを示す符号CSも得て出力する。なお、指標Sと間隔T自体は実施例1変形例1の周期性分析部131と同じである。
周期性統合包絡生成部250は、少なくとも、周期性包絡系列P[1],…,P[N]、振幅スペクトル包絡系列W[1],…,W[N]を入力とし、周期性統合包絡系列WM[1],…,WM[N]を求めて周期性統合包絡WM[n]を出力する。また、周期性統合包絡生成部150は、値δとして、予め定めた1つの値ではなく、予め定めた複数の候補値のうちの何れかを選択する場合には、係数列X[1], …, X[N]も入力とし、予め定めた複数の候補値のうち周期性統合包絡WM[n]と係数X[n]の絶対値系列の形状が近くなる候補値を値δとして求め、値δを示す符号Cδも出力する(S250)。
可変長符号化パラメータ計算部260は、周期性統合包絡系列WM[1],…,WM[N]と平滑化振幅スペクトル包絡系列~W[1],…,~W[N]と正規化係数列XN[1],…,XN[N]を入力とし、可変長符号化パラメータrnを求める(S260)。可変長符号化パラメータ計算部260は、周期性統合包絡系列WM[1],…,WM[N]から求めた振幅値に依存して可変長符号化パラメータrnを計算することを特徴としている。
可変長符号化部270は、可変長符号化パラメータ計算部260で求めた可変長符号化パラメータrnを用いて正規化係数列XN[1],…,XN[N]を可変長符号化し、可変長符号CXを出力する(S270)。例えば、可変長符号化部270は、可変長符号化パラメータ計算部260で求めたライスパラメータrnを用いて正規化係数列XN[1],…,XN[N]をライス符号化し、得られた符号を可変長符号CXとして出力する。可変長符号化パラメータ計算部260で求めたライスパラメータrnは、周期性統合包絡系列の振幅値に依存する可変長符号化パラメータであり、周期性統合包絡系列の値が大きい周波数ほど大きな値となっている。ライス符号化は、振幅値に依存する可変長符号化の公知技術のうちの1つであり、ライスパラメータrnを用いて振幅値に依存する可変長符号化を行うものである。また、周期性統合包絡生成部250で生成した周期性統合包絡系列は、入力音響信号のスペクトル包絡を高精度に表現するものである。すなわち、可変長符号化部270は、周期性統合包絡系列の値が大きい周波数ほど、前記入力音響信号の周波数領域の係数列であるX[1],…,X[N]の振幅が大きいとことを前提に、正規化係数列XN[1],…,XN[N]を可変長符号化していることになり、言い換えれば、可変長符号化パラメータを用いて、振幅値に依存する可変長符号化により、正規化係数列XN[1],…,XN[N]を符号化していることになる。ここでいう振幅値とは、符号化対象の係数列の平均振幅値、係数列に含まれる各係数の振幅の推定値、係数列の振幅の包絡の推定値などである。
なお、符号化装置としては、周期性包絡系列生成部140と周期性統合包絡生成部250と可変長符号化パラメータ計算部260と可変長符号化部270だけを備え、符号化装置の外部で生成された平滑化振幅スペクトル包絡系列~W[1],…,~W[N]と、正規化係数列XN[1],…,XN[N]、間隔Tと、必要に応じて振幅スペクトル包絡系列W[1],…, W[N]と、必要に応じて指標Sとを入力とし、可変長符号CXを出力してもよい。
上述の周期性分析部230では正規化係数列XN[1],…,XN[N]を入力として間隔Tを求めているが、周期性分析部230では周波数領域変換部110が出力した係数列X[1],…,X[N]を入力として間隔Tを求めてもよい。この場合は、実施例1の周期性分析部130と同じ方法で間隔Tを求める。
図7に実施例2の復号装置の機能構成例を、図8に実施例2の復号装置の処理フローを示す。復号装置400は、スペクトル包絡系列計算部421、周期性包絡系列生成部440、周期性統合包絡生成部450、可変長符号化パラメータ計算部460、可変長復号部470、周波数領域系列逆正規化部411、周波数領域逆変換部410を備える。復号装置400は、量子化済線形予測係数^α1,…,^αPを示す符号CL、間隔Tを示す符号CT、正規化係数列XN[1],…,XN[N]を可変長符号化した可変長符号CXを受け取り、音響信号を出力する。なお、必要に応じて値δを示す符号Cδと基準となる可変長符号化パラメータsbを示す符号Csbと指標Sを示す符号CSも受け取る。以下に、各構成部の詳細を示す。
スペクトル包絡系列計算部421は、符号CLを入力とし、振幅スペクトル包絡系列W[1],…,W[N]と平滑化振幅スペクトル包絡系列~W[1],…,~W[N]を計算する(S421)。より具体的には、以下の手順で処理すればよい。
周期性包絡系列生成部440は、間隔Tを示す符号CTを入力とし、符号CTを復号し、間隔Tを得る。そして、符号化装置200の周期性包絡系列生成部140と同じ方法で周期性包絡系列P[1],…,P[N]を求め、出力する(S440)。
周期性統合包絡生成部450には、周期性包絡系列P[1],…,P[N]、振幅スペクトル包絡系列W[1],…,W[N]、符号Cδ、符号CSが入力される。ただし、符号Cδ、符号CSは入力されない場合もある。周期性統合包絡生成部450は、符号Cδを復号し、値δを取得する。ただし、符号Cδが入力されない場合は、符号Cδの復号は行わず、周期性統合包絡生成部450に予め記憶された値δを取得する。なお、周期性統合包絡生成部450は、符号CSが入力された場合には、符号CSを復号して指標Sを取得し、取得した指標Sが、周期性が高いことに対応するフレームの場合には符号Cδを復号して値δを取得し、取得した指標Sが、周期性が低いことに対応するフレームである場合には符号Cδの復号は行わず、周期性統合包絡生成部450に予め記憶された値δを取得する。そして、周期性統合包絡生成部450は、式(6)によって、周期性統合包絡系列WM[1],…,WM[N]を求める。(S450)
可変長符号化パラメータ計算部460は、周期性統合包絡系列WM[1],…,WM[N]と平滑化振幅スペクトル包絡系列~W[1],…,~W[N]と符号Csbを入力とし、可変長符号化パラメータrnを得る(S460)。ただし、復号装置400に伝送される別の情報から振幅の平均値を推定できる場合は、別の情報から推定した振幅の平均値の推定値からsbを近似的に決定する方法を決めておいてもよい。この場合は、符号Csbは入力されない。以下に、1サンプルごとにライス復号を行う場合を例に、可変長符号化パラメータの計算方法を説明する。
可変長復号部470は、可変長符号化パラメータ計算部460で求めた可変長符号化パラメータrnを用いて可変長符号CXを復号して復号正規化係数列^XN[1],…,^XN[N]を得る(S470)。例えば、可変長復号部470は、可変長符号化パラメータ計算部460で求めたライスパラメータrnを用いて可変長符号CXを復号して復号正規化係数列^XN[1],…,^XN[N]を得る。可変長復号部470の復号方法は、可変長符号化部270の符号化方法に対応するものである。
周波数領域系列逆正規化部411は、復号正規化係数列^XN[1],…,^XN[N]と平滑化振幅スペクトル包絡系列~W[1],…,~W[N]を入力とし、
^X[n]=^XN[n]・~W[n] (15)
のように、復号係数列^X[1],…,^X[N]を求めて出力する(S411)。
周波数領域逆変換部410は、復号係数列^X[1],…,^X[N]を入力とし、復号係数列^X[1],…,^X[N]を所定の時間区間であるフレーム単位の音響信号(時間領域)に変換する(S410)。
なお、復号装置としては、周期性包絡系列生成部440と周期性統合包絡生成部450と可変長符号化パラメータ計算部460と可変長復号部470だけを備え、復号装置に必要に応じて入力される符号Cδと符号Csbに加えて、復号装置の外部で得られた平滑化振幅スペクトル包絡系列~W[1],…,~W[N]、振幅スペクトル包絡系列W[1],…,W[N]、間隔T、必要に応じて指標Sも入力とし、正規化係数列XN[1],…,XN[N]を出力し、外部で平滑化振幅スペクトル包絡系列を乗算して時間領域の音響信号に変換してもよい。
可変長符号化は、符号化対象の入力値の振幅の取りうる範囲に合わせて適応的に符号を決定することで符号化効率を向上させる符号化方法である。実施例2では周波数領域の係数列である正規化係数列XN[1],…,XN[N]を符号化対象としているが、符号化対象の係数列に含まれる各係数の振幅の情報をより正確に用いて求めた可変長符号化パラメータを用いて可変長符号化をすれば符号化装置が行う可変長符号化自体の符号化効率は高くなる。しかし、復号装置が可変長符号化パラメータを求めるために、符号化装置から復号装置に対して符号化対象の係数列に含まれる各係数の振幅の情報をより正確に送る必要があり、その分だけ符号化装置から復号装置に送る符号量が増大してしまう。
・量子化済線形予測係数^α1,…,^αPの情報(符号CL)
・間隔Tを示す情報(符号CT)
・値δを示す情報(符号Cδ)
である。すなわち、実施例2の符号化装置と復号装置によれば、符号化装置に入力された入力音響信号のピッチ周期に起因する振幅のピークを含む包絡を、符号CL、符号CT、符号Cδのみの少ない情報量で、復号装置で再現することが可能となる。
上述の効果を得るというポイントで実施例2の符号化装置、復号装置を考えると、符号化装置200が、
・所定時間区間の入力音響信号から求めた線形予測係数符号に対応する周波数領域の系列であるスペクトル包絡系列と、入力音響信号から求めた周期符号に対応する周波数領域の周期と、に基づく周波数領域の系列である周期性統合包絡系列を生成する周期性統合包絡生成部250
・周期性統合包絡系列の値が大きい周波数ほど、入力音響信号の振幅が大きいことを前提に、入力音響信号に由来する周波数領域の系列を符号化する可変長符号化部270
を有し、復号装置400が、
・線形予測係数符号に対応する周波数領域の系列であるスペクトル包絡系列と、周期符号に対応する周波数領域の周期と、に基づく周波数領域の系列である周期性統合包絡系列を生成する周期性統合包絡生成部450
・周期性統合包絡系列の値が大きい周波数ほど、音響信号の振幅が大きいことを前提に、可変長符号を復号して周波数領域の系列を得る可変長復号部470、
を有することを特徴とすればよい。なお、「周期性統合包絡系列の値が大きい周波数ほど、入力音響信号の振幅が大きいことを前提に」と「周期性統合包絡系列の値が大きい周波数ほど、音響信号の振幅が大きいことを前提に」とは、周期性統合包絡系列が、入力音響信号または音響信号の振幅の大きい周波数において大きい値になることを特徴としていることを示している。また、「入力音響信号に由来する」とは、入力音響信号から求められることや入力音響信号に対応していることを意味している。例えば、係数列X[1],…,X[N]や正規化係数列XN[1],…,XN[N]は、入力音響信号に由来する周波数領域の系列である。
図9に実施例3の符号化装置の機能構成例を、図10に実施例3の符号化装置の処理フローを示す。符号化装置300は、スペクトル包絡系列計算部221、周波数領域変換部110、周波数領域系列正規化部111、周期性分析部330、周期性包絡系列生成部140、周期性統合包絡生成部250、可変長符号化パラメータ計算部260、第2可変長符号化パラメータ計算部380、可変長符号化部370を備える。符号化装置300は、入力された時間領域の音響ディジタル信号を入力音響信号x(t)とし、少なくとも量子化済線形予測係数^α1,…,^αPを示す符号CL、正規化係数列XN[1],…,XN[N]の周期を表す間隔Tの符号CT、係数列X[1],…,X[N]または正規化係数列XN[1],…,XN[N]の周期性の程度を示す所定の指標Sと指標Sを示す符号CS、正規化係数列XN[1],…,XN[N]を可変長符号化した可変長符号CXを出力する。周波数領域系列正規化部111は実施例1変形例1と同じである。周波数領域変換部110と周期性包絡系列生成部140は実施例1と同じである。振幅スペクトル包絡系列計算部221、周期性統合包絡生成部250、可変長符号化パラメータ計算部260は、実施例2と同じである。以下では異なる構成部について説明する。
周期性分析部330は、正規化係数列XN[1],…,XN[N]を入力とし、
当該正規化係数列XN[1],…,XN[N]の周期性の程度を示す指標Sと間隔T(周期的に大きな値となる間隔)とを求め、指標Sと指標Sを示す符号CSと間隔Tと間隔Tを示す符号CTを出力する(S330)。なお、指標Sと間隔T自体は実施例1変形例1の周期性分析部131と同じである。
第2可変長符号化パラメータ計算部380は、振幅スペクトル包絡系列W[1],…,W[N]と平滑化振幅スペクトル包絡系列~W[1],…,~W[N]と正規化係数列XN[1],…,XN[N]を入力とし、可変長符号化パラメータrnを求める(S380)。可変長符号化パラメータ計算部260は、周期性統合包絡系列WM[1],…,WM[N]から求めた振幅値に依存して可変長符号化パラメータrnを計算することを特徴としているのに対して、第2可変長符号化パラメータ計算部380は、振幅スペクトル包絡系列から求めた振幅値に依存して可変長符号化パラメータを計算することを特徴としている。以下に、1サンプルごとにライス符号化を行う場合を例に、可変長符号化パラメータの計算方法を説明する。
可変長符号化部370は、可変長符号化パラメータrnを用いて正規化係数列XN[1],…,XN[N]を可変長符号化し、可変長符号CXを出力する(S370)。ただし、可変長符号化パラメータrnは、指標Sがあらかじめ定めた周期性の程度が大きいことを示す範囲の場合は、可変長符号化パラメータ計算部260が計算した可変長符号化パラメータrnであり、指標Sがあらかじめ定めた周期性の程度が大きいことを示す範囲ではない場合は、第2可変長符号化パラメータ計算部380が計算した可変長符号化パラメータrnである。
なお、符号化装置としては、周期性包絡系列生成部140と周期性統合包絡生成部250と可変長符号化パラメータ計算部260と第2可変長符号化パラメータ計算部380と可変長符号化部370だけを備え、符号化装置の外部で生成された平滑化振幅スペクトル包絡系列~W[1],…,~W[N]と正規化係数列XN[1],…,XN[N]、間隔Tと、必要に応じて振幅スペクトル包絡系列W[1],…, W[N]と、必要に応じて指標Sとを入力とし、可変長符号CXを出力してもよい。
上述の周期性分析部330では正規化係数列XN[1],…,XN[N]を入力として間隔Tを求めているが、周期性分析部330では周波数領域変換部110が出力した係数列X [1],…,X [N]を入力として間隔Tを求めてもよい。この場合は、実施例1の周期性分析部130と同じ方法で間隔Tを求める。
図11に実施例3の復号装置の機能構成例を、図12に実施例3の復号装置の処理フローを示す。復号装置500は、スペクトル包絡系列計算部421、指標復号部530、周期性包絡系列生成部440、周期性統合包絡生成部450、可変長符号化パラメータ計算部460、第2可変長符号化パラメータ計算部580、可変長復号部570、周波数領域系列逆正規化部411、周波数領域逆変換部410を備える。復号装置500は、量子化済線形予測係数^α1,…,^αPを示す符号CL、指標Sを示す符号CS、間隔Tを示す符号CT、正規化係数列XN[1],…,XN[N]を可変長符号化した可変長符号CXを受け取り、音響信号を出力する。なお、必要に応じて値δを示す符号Cδと基準となる可変長符号化パラメータsbを示す符号Csbも受け取る。スペクトル包絡系列計算部421、周期性包絡系列生成部440、周期性統合包絡生成部450、可変長符号化パラメータ計算部460、周波数領域系列逆正規化部411、周波数領域逆変換部410は実施例2と同じである。以下では異なる構成部について説明する。
指標復号部530は、符号CSを復号し、指標Sを得る。復号装置500では、指標Sがあらかじめ定めた周期性の程度が大きいことを示す範囲の場合は、可変長符号化パラメータ計算部460が可変長符号化パラメータrnを計算し、指標Sがあらかじめ定めた周期性の程度が大きいことを示す範囲ではない場合は、第2可変長符号化パラメータ計算部580が可変長符号化パラメータrnを計算する(S590)。なお、「あらかじめ定めた周期性の程度が大きいことを示す範囲」は、符号化装置300と同じ範囲である。
第2可変長符号化パラメータ計算部580は、振幅スペクトル包絡系列W[1],…,W[N]と平滑化振幅スペクトル包絡系列~W[1],…,~W[N]と符号Csbを入力とし、可変長符号化パラメータrnを求める(S580)。ただし、復号装置500に伝送される別の情報から振幅の平均値を推定できる場合は、別の情報から推定した振幅の平均値の推定値からsbを近似的に決定する方法を決めておいてもよい。この場合は、符号Csbは入力されない。以下に、1サンプルごとにライス復号を行う場合を例に、可変長符号化パラメータの計算方法を説明する。
可変長復号部570は、可変長符号化パラメータrnを用いて可変長符号CXを復号して復号正規化係数列^XN[1],…,^XN[N]を求める(S570)。ただし、可変長符号化パラメータrnは、指標Sがあらかじめ定めた周期性の程度が大きいことを示す範囲の場合は、可変長符号化パラメータ計算部460が計算した可変長符号化パラメータrnであり、指標Sがあらかじめ定めた周期性の程度が大きいことを示す範囲ではない場合は、第2可変長符号化パラメータ計算部580が計算した可変長符号化パラメータrnである。
なお、復号装置としては、周期性包絡系列生成部440と周期性統合包絡生成部450と可変長符号化パラメータ計算部460と第2可変長符号化パラメータ計算部580と可変長復号部570だけを備え、復号装置に必要に応じて入力される符号Cδと符号Csbに加えて、復号装置の外部で得られた平滑化振幅スペクトル包絡系列~W[1],…,~W[N]、振幅スペクトル包絡系列W[1],…,W[N]、間隔T、指標Sも入力とし、正規化係数列XN[1],…,XN[N]を出力し、外部で平滑化振幅スペクトル包絡系列を乗算して時間領域の音響信号に変換してもよい。
入力音響信号の周期性の程度が小さい場合には、入力音響信号のピッチ周期に起因する振幅のピークは小さい。そこで、実施例3の符号化装置、復号装置は、符号化の対象となる音響信号の周期性の程度が大きい場合には周期性統合包絡系列を用いて可変長符号化パラメータを求め、符号化の対象となる音響信号の周期性の程度が大きくない場合には振幅スペクトル包絡系列を用いて可変長符号化パラメータを求めるため、より適した可変長符号化パラメータを用いて可変長符号化でき、符号化精度を上げることができるという効果がある。
上述の各種の処理は、記載に従って時系列に実行されるのみならず、処理を実行する装置の処理能力あるいは必要に応じて並列的にあるいは個別に実行されてもよい。その他、本発明の趣旨を逸脱しない範囲で適宜変更が可能であることはいうまでもない。
110 周波数領域変換部 111 周波数領域係数正規化部
120、121、221、421 スペクトル包絡系列計算部
130,131、230、330 周期性分析部
140、440 周期性包絡系列生成部
150、250、450 周期性統合包絡生成部
200、300 符号化装置
260、360、460 可変長符号化パラメータ計算部
270、370 可変長符号化部
380、580 第2可変長符号化パラメータ計算部
400、500 復号装置
410 周波数領域逆変換部 411 周波数領域系列逆正規化部
470、570 可変長復号部 530 指標復号部
Claims (20)
- 所定時間区間の入力音響信号から求めた線形予測係数符号に対応する周波数領域の系列であるスペクトル包絡系列と、前記入力音響信号から求めた周期符号に対応する周波数領域の周期と、に基づく周波数領域の系列である周期性統合包絡系列を生成する周期性統合包絡生成部と、
前記周期性統合包絡系列から振幅値に依存する可変長符号化パラメータを計算する可変長符号化パラメータ計算部と、
可変長符号化パラメータを用いて、振幅値に依存する可変長符号化により、前記入力音響信号に由来する周波数領域の系列を符号化する可変長符号化部、
を備える符号化装置。 - 所定時間区間の入力音響信号から求めた線形予測係数符号に対応する周波数領域の系列であるスペクトル包絡系列と、前記入力音響信号から求めた周期符号に対応する周波数領域の周期と、に基づく周波数領域の系列である周期性統合包絡系列を生成する周期性統合包絡生成部と、
前記周期性統合包絡系列の値が大きい周波数ほど、前記入力音響信号の振幅が大きいことを前提に、前記入力音響信号に由来する周波数領域の系列を符号化する可変長符号化部、
を備える符号化装置。 - 請求項1記載の符号化装置であって、
前記スペクトル包絡系列から振幅値に依存する可変長符号化パラメータを計算する第2可変長符号化パラメータ計算部も備え、
前記可変長符号化部は、
前記入力音響信号の周期性の程度を示す指標があらかじめ定めた周期性の程度が大きいことを示す範囲の場合は、前記可変長符号化パラメータ計算部が計算した可変長符号化パラメータを用いて符号化し、
前記周期性の程度を示す指標が前記の周期性の程度が大きいことを示す範囲ではない場合は、前記第2可変長符号化パラメータ計算部が計算した可変長符号化パラメータを用いて符号化する
符号化装置。 - 請求項2記載の符号化装置であって、
前記可変長符号化部は、
前記入力音響信号の周期性の程度を示す指標があらかじめ定めた周期性の程度が大きいことを示す範囲の場合は、前記周期性統合包絡系列の値が大きい周波数ほど、前記入力音響信号の振幅が大きいことを前提に、前記入力音響信号に由来する周波数領域の系列を符号化し、
前記指標が前記の周期性の程度が大きいことを示す範囲ではない場合は、前記スペクトル包絡系列の値が大きい周波数ほど、前記入力音響信号の振幅が大きいことを前提に、前記入力音響信号に由来する周波数領域の系列を符号化する
符号化装置。 - 線形予測係数符号に対応する周波数領域の系列であるスペクトル包絡系列と、周期符号に対応する周波数領域の周期と、に基づく周波数領域の系列である周期性統合包絡系列を生成する周期性統合包絡生成部と、
前記周期性統合包絡系列から振幅値に依存する可変長符号化パラメータを計算する可変長符号化パラメータ計算部と、
可変長符号化パラメータを用いて復号する可変長復号部、
を備える復号装置。 - 線形予測係数符号に対応する周波数領域の系列であるスペクトル包絡系列と、周期符号に対応する周波数領域の周期と、に基づく周波数領域の系列である周期性統合包絡系列を生成する周期性統合包絡生成部と、
前記周期性統合包絡系列の値が大きい周波数ほど、音響信号の振幅が大きいことを前提に、可変長符号を復号して周波数領域の系列を得る可変長復号部、
を備える復号装置。 - 請求項5記載の復号装置であって、
入力された指標符号を復号して周期性の程度を示す指標を得る指標復号部と、
前記スペクトル包絡系列から振幅値に依存する可変長符号化パラメータを計算する第2可変長符号化パラメータ計算部
も備え、
前記可変長復号部は、
前記指標があらかじめ定めた周期性の程度が大きいことを示す範囲の場合は、前記可変長符号化パラメータ計算部が計算した可変長符号化パラメータを用いて復号し、
前記指標が前記の周期性の程度が大きいことを示す範囲ではない場合は、前記第2可変長符号化パラメータ計算部が計算した可変長符号化パラメータを用いて復号する
復号装置。 - 請求項6記載の復号装置であって、
前記可変長復号部は、
入力された周期性の程度を示す指標があらかじめ定めた周期性の程度が大きいことを示す範囲の場合は、前記周期性統合包絡系列の値が大きい周波数ほど、音響信号の振幅が大きいことを前提に、前記可変長符号を復号して周波数領域の系列を得て、
前記指標があらかじめ定めた周期性の程度が大きいことを示す範囲ではない場合は、前記スペクトル包絡系列の値が大きい周波数ほど、音響信号の振幅が大きいことを前提に、前記可変長符号を復号して周波数領域の系列を得る
復号装置。 - 所定時間区間の入力音響信号から求めた線形予測係数符号に対応する周波数領域の系列であるスペクトル包絡系列と、前記入力音響信号から求めた周期符号に対応する周波数領域の周期と、に基づく周波数領域の系列である周期性統合包絡系列を生成する周期性統合包絡生成ステップと、
前記周期性統合包絡系列から振幅値に依存する可変長符号化パラメータを計算する可変長符号化パラメータ計算ステップと、
可変長符号化パラメータを用いて、振幅値に依存する可変長符号化により、前記入力音響信号に由来する周波数領域の系列を符号化する可変長符号化ステップ、
を実行する符号化方法。 - 所定時間区間の入力音響信号から求めた線形予測係数符号に対応する周波数領域の系列であるスペクトル包絡系列と、前記入力音響信号から求めた周期符号に対応する周波数領域の周期と、に基づく周波数領域の系列である周期性統合包絡系列を生成する周期性統合包絡生成ステップと、
前記周期性統合包絡系列の値が大きい周波数ほど、前記入力音響信号の振幅が大きいことを前提に、前記入力音響信号に由来する周波数領域の系列を符号化する可変長符号化ステップ、
を実行する符号化方法。 - 請求項9記載の符号化方法であって、
前記スペクトル包絡系列から振幅値に依存する可変長符号化パラメータを計算する第2可変長符号化パラメータ計算ステップも有し、
前記可変長符号化ステップは、
前記入力音響信号の周期性の程度を示す指標があらかじめ定めた周期性の程度が大きいことを示す範囲の場合は、前記可変長符号化パラメータ計算ステップで計算した可変長符号化パラメータを用いて符号化し、
前記周期性の程度を示す指標が前記の周期性の程度が大きいことを示す範囲ではない場合は、前記第2可変長符号化パラメータ計算ステップで計算した可変長符号化パラメータを用いて符号化する
符号化方法。 - 請求項10記載の符号化方法であって、
前記可変長符号化ステップは、
前記入力音響信号の周期性の程度を示す指標があらかじめ定めた周期性の程度が大きいことを示す範囲の場合は、前記周期性統合包絡系列の値が大きい周波数ほど、前記入力音響信号の振幅が大きいことを前提に、前記入力音響信号に由来する周波数領域の系列を符号化し、
前記指標が前記の周期性の程度が大きいことを示す範囲ではない場合は、前記スペクトル包絡系列の値が大きい周波数ほど、前記入力音響信号の振幅が大きいことを前提に、前記入力音響信号に由来する周波数領域の系列を符号化する
符号化方法。 - 線形予測係数符号に対応する周波数領域の系列であるスペクトル包絡系列と、周期符号に対応する周波数領域の周期と、に基づく周波数領域の系列である周期性統合包絡系列を生成する周期性統合包絡生成ステップと、
前記周期性統合包絡系列から振幅値に依存する可変長符号化パラメータを計算する可変長符号化パラメータ計算ステップと、
可変長符号化パラメータを用いて復号する可変長復号ステップ、
を実行する復号方法。 - 線形予測係数符号に対応する周波数領域の系列であるスペクトル包絡系列と、周期符号に対応する周波数領域の周期と、に基づく周波数領域の系列である周期性統合包絡系列を生成する周期性統合包絡生成ステップと、
前記周期性統合包絡系列の値が大きい周波数ほど、音響信号の振幅が大きいことを前提に、可変長符号を復号して周波数領域の系列を得る可変長復号ステップ、
を実行する復号方法。 - 請求項13記載の復号方法であって、
入力された指標符号を復号して周期性の程度を示す指標を得る指標復号ステップと、
前記スペクトル包絡系列から振幅値に依存する可変長符号化パラメータを計算する第2可変長符号化パラメータ計算ステップ
も有し、
前記可変長復号ステップは、
前記指標があらかじめ定めた周期性の程度が大きいことを示す範囲の場合は、前記可変長符号化パラメータ計算ステップで計算した可変長符号化パラメータを用いて復号し、
前記指標が前記の周期性の程度が大きいことを示す範囲ではない場合は、前記第2可変長符号化パラメータ計算ステップで計算した可変長符号化パラメータを用いて復号する
復号方法。 - 請求項14記載の復号方法であって、
前記可変長復号ステップは、
入力された周期性の程度を示す指標があらかじめ定めた周期性の程度が大きいことを示す範囲の場合は、前記周期性統合包絡系列の値が大きい周波数ほど、音響信号の振幅が大きいことを前提に、前記可変長符号を復号して周波数領域の系列を得て、
前記指標があらかじめ定めた周期性の程度が大きいことを示す範囲ではない場合は、前記スペクトル包絡系列の値が大きい周波数ほど、音響信号の振幅が大きいことを前提に、前記可変長符号を復号して周波数領域の系列を得る
復号方法。 - 請求項1から4のいずれかの符号化装置としてコンピュータを機能させるための符号化プログラム。
- 請求項5から8のいずれかの復号装置としてコンピュータを機能させるための復号プログラム。
- 請求項1から4のいずれかの符号化装置としてコンピュータを機能させるための符号化プログラムを記録したコンピュータが読み取り可能な記録媒体。
- 請求項5から8のいずれかの復号装置としてコンピュータを機能させるための復号プログラムを記録したコンピュータが読み取り可能な記録媒体。
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