Encoding apparatus and encoding method

An encoding device and an encoding method are provided for encoding by reducing the number of samples to be processed when encoding higher-band spectrum data according to lower-band spectrum data in a wide-band signal. The device and the method can obtain a high-quality decoded signal even if a large quantization distortion is caused in the lower-band spectrum data. When encoding higher-band spectrum data in a signal to be encoded, according to lower-band spectrum data in the signal, only for a part (a head portion) of the higher-band spectrum data, the lower-band spectrum data after being quantized is subjected to approximate partial search and higher-band spectrum data is generated according to the search result.

TECHNICAL FIELD

The present invention relates to a encoding apparatus and encoding method used in a communication system for encoding and transmitting signals.

BACKGROUND ART

When speech/sound signals are transmitted in a packet communication system represented by Internet communication, mobile communication system and so on, compression/coding techniques are often used to improve the transmission efficiency of speech/sound signals. Furthermore, in the recent years, while speech/sound signals are being encoded simply at low bit rates, there is a growing demand for techniques for encoding speech/sound signals of wider band.

To meet this demand, studies are underway to develop various techniques for encoding wideband speech/sound signals without drastically increasing the amount of encoded information. For example, patent document 1 discloses a technique of generating features of the high frequency band region in the spectral data obtained by converting an input acoustic signal of a certain period, as side information, and outputting this information together with encoded information of the low band region. To be more specific, the spectral data of the high frequency band region is divided into a plurality of groups, and, in each group, regards the spectrum of the low band region that is the most similar to the spectrum of the group, as the side information mentioned above.

Furthermore, patent document 2 discloses a technique of dividing the high band signal into a plurality of subbands, deciding, per subband, the degree of similarity between the signal of each subband and the low band signal, and changing the configurations of side information (i.e. the amplitude parameter of the subband, position parameter of a similar low band signal, residual signal parameter between the high band the and the low band) according to the decision result.

DISCLOSURE OF INVENTION

Problems to be Solved by the Invention

However, although the techniques disclosed in above-described patent document 1 and patent document 2 decide a low band signal that correlates with or that is similar to a high band region to generate a high band signal (i.e. spectral data of a high band region), this is performed per subband (group) of the high band signal, and, as a result, the amount of processing of calculations becomes enormous. Furthermore, since the above-described processing is carried out on a per band basis, not only the amount of calculation, but also the amount of information required to encode side information increases.

Furthermore, the techniques disclosed in above-described patent document 1 and patent document 2 decide the degree of similarity of spectral data of the high band region of an input signal in the same way as spectral data of the low band region of the input signal, and, given that spectral data of the low band region is not taken into account if it is distorted by quantization, a severe sound quality degradation is anticipated when spectral data of the low band region is distorted by quantization.

It is therefore an object of the present invention to provide an encoding apparatus and encoding method that make it possible to encode spectral data of the high band region of a wideband signal based on spectral data of the low band region of the signal by reducing the number of samples to be processed and furthermore obtain a decoded signal of high quality even when a severe quantization distortion occurs in the spectral data of the low band region.

Means for Solving the Problem

The encoding apparatus of the present invention adopts a configuration including: a first encoding section that encodes an input signal to generate first encoded information; a decoding section that decodes the first encoded information to generate a decoded signal; a orthogonal transform section that orthogonal-transforms the input signal and the decoded signal to generate orthogonal transform coefficients for the signals; a second encoding section that generates second encoded information representing a high band part in the orthogonal transform coefficients of the decoded signal, based on the orthogonal transform coefficients of the input signal and the orthogonal transform coefficients of the decoded signal; and an integration section that integrates the first encoded information and the second encoded information.

The encoding method of the present invention includes: a first encoding step of encoding an input signal to generate first encoded information; a decoding step of decoding the first encoded information to generate a decoded signal; a orthogonal transform step of orthogonal-transforming the input signal and the decoded signal to generate orthogonal transform coefficients for the signals; a second encoding step of generating second encoded information representing a high band part of the orthogonal transform coefficients of the decoded signal based on the orthogonal transform coefficients of the input signal and the orthogonal transform coefficients of the decoded signal; and an integration step of integrating the first encoded information and the second encoded information.

Advantageous Effect of the Invention

In accordance with the present invention, it is possible to encode spectral data of the high band region of a wideband signal based on spectral data of the low band region of the wideband signal by reducing the number of samples to be processed and furthermore obtain a decoded signal of high quality even when a severe quantization distortion occurs in the spectral data of the low band region.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be explained below in detail with reference to the accompanying drawings.

FIG. 1is a block diagram showing a configuration of a communication system with a encoding apparatus and decoding apparatus according to Embodiment 1 of the present invention. InFIG. 1, the communication system is provided with a encoding apparatus and decoding apparatus, which are able to communicate with each other via a channel. The channel may be wireless or wired or may be both wireless and wired.

Encoding apparatus101divides an input signal every N samples (N is a natural number), regards N samples one frame, and performs encoding per frame. Here, suppose the input signal to be encoded is expressed as “xn” (n=0, . . . , N−1). n indicates the (n+1)-th signal element of the input signal divided every N samples. The encoded input information (i.e. encoded information) is transmitted to decoding apparatus103via channel102.

Decoding apparatus103receives the encoded information transmitted from encoding apparatus101via channel102, decodes the signal and obtains an output signal.

FIG. 2is a block diagram showing an internal configuration of encoding apparatus101shown inFIG. 1. When the sampling frequency of the input signal is SRinput, down-sampling processing section201down-samples the sampling frequency of the input signal from SRinputto SRbase(SRbase<SRinput), and outputs the down-sampled input signal to low band encoding section202as the down-sampled input signal.

Low band encoding section202encodes the down-sampled input signal outputted from down-sampling processing section201using a CELP type speech encoding method, to generate a low band component encoded information, and outputs the low band component encoded information generated, to low band decoding section203and encoded information integration section207. The details of low band encoding section202will be described later.

Low band decoding section203decodes the low band component encoded information outputted from low band encoding section202using a CELP type speech decoding method, to generate a low band component decoded signal, and outputs the low band component decoded signal generated, to up-sampling processing section204. The details of low band decoding section203will be described later.

Up-sampling processing section204up-samples the sampling frequency of the low band component decoded signal outputted from low band decoding section203from SRbaseto SRinput, and outputs the up-sampled low band component decoded signal to orthogonal transform processing section205as the up-sampled low band component decoded signal.

Next, as for the orthogonal transform processing in orthogonal transform processing section205, the calculation procedures and data output to the internal buffers will be explained.

Orthogonal transform processing section205applies the modified discrete cosine transform (“MDCT”) to input signal xnand up-sampled low band component decoded signal ynoutputted from up-sampling processing section204and calculates MDCT coefficients Xkof the input signal and MDCT coefficients Ykof up-sampled low band component decoded signal ynaccording to equation 3 and equation 4.

Here, k is the index of each sample in a frame. Orthogonal transform processing section205calculates xn′, which is a vector combining input signal xnand buffer buf1n, according to following equation 5. Furthermore, orthogonal transform processing section205calculates which is a vector combining up-sampled low band component decoded signal ynand buffer buf2n, according to following equation 6.

Orthogonal transform processing section205outputs the MDCT coefficients Xkof the input signal and MDCT coefficients Ykof the up-sampled low band component decoded signal, to high band encoding section206.

High band encoding section206generates a high band component encoded information from the values of MDCT coefficients Xkof the input signal outputted from orthogonal transform processing section205and MDCT coefficients Ykof the up-sampled low band component decoded signal, and outputs the high band component encoded information generated, to encoded information integration section207. The details of high band encoding section206will be described later.

Encoded information integration section207integrates the low band component encoded information outputted from low band encoding section202with the high band component encoded information outputted from high band encoding section206, adds, if necessary, a transmission error code and so on, to the integrated encoded information, and outputs the resulting code to channel102as encoded information.

Next, the internal configuration of low band encoding section202shown inFIG. 2will be explained usingFIG. 3. Here, a case where low band encoding section202performs CELP type speech encoding, will be explained. Pre-processing section301performs high pass filter processing of removing the DC component, waveform shaping processing or pre-emphasis processing, with the input signal, to improve the performance of subsequent encoding processing, and outputs the signal (Xin) subjected to such processing to LPC analysis section302and addition section305.

LPC analysis section302performs a linear predictive analysis using Xin outputted from pre-processing section301, and outputs the analysis result (linear predictive analysis coefficient) to LPC quantization section303.

LPC quantization section303performs quantization processing of the linear predictive coefficient (LPC) outputted from LPC analysis section302, outputs the quantized LPC to synthesis filter304and also outputs a code (L) representing the quantized LPC, to multiplexing section314.

Synthesis filter304performs a filter synthesis on an excitation outputted from addition section311(described later) using a filter coefficient based on the quantized LPC outputted from LPC quantization section303, generates a synthesized signal and outputs the synthesized signal to addition section305.

Addition section305inverts the polarity of the synthesized signal outputted from synthesis filter304, adds the synthesized signal with an inverse polarity to Xin outputted from pre-processing section301, thereby calculating an error signal, and outputs the error signal to perceptual weighting section312.

Adaptive excitation codebook306stores excitation outputted in the past from addition section311in a buffer, extracts one frame of samples from the past excitation specified by the signal outputted from parameter determining section313(described later) as an adaptive excitation vector, and outputs this vector to multiplication section309.

Quantization gain generation section307outputs a quantization adaptive excitation gain and quantization fixed excitation gain specified by the signal outputted from parameter determining section313, to multiplication section309and multiplication section310, respectively.

Fixed excitation codebook308outputs a pulse excitation vector having a shape specified by a signal outputted from parameter determining section313, to multiplication section310as a fixed excitation vector. A vector produced by multiplying the pulse excitation vector by a spreading vector may also be outputted to multiplication section310as a fixed excitation vector.

Multiplication section309multiplies the adaptive excitation vector outputted from adaptive excitation codebook306by the quantization adaptive excitation gain outputted from quantization gain generation section307, and outputs the multiplication result to addition section311. Furthermore, multiplication section310multiplies the fixed excitation vector outputted from fixed excitation codebook308by the quantization fixed excitation gain outputted from quantization gain generation section307, and outputs the multiplication result to addition section311.

Addition section311adds up the adaptive excitation vector multiplied by the gain outputted from multiplication section309and the fixed excitation vector multiplied by the gain outputted from multiplication section310, and outputs an excitation, which is the addition result, to synthesis filter304and adaptive excitation codebook306. The excitation outputted to adaptive excitation codebook306is stored in the buffer of adaptive excitation codebook306.

Perceptual weighting section312assigns perceptual a weight to the error signal outputted from addition section305, and outputs the resulting error signal to parameter determining section313as the coding distortion.

Parameter determining section313selects the adaptive excitation vector, fixed excitation vector and quantization gain that minimize the coding distortion outputted from perceptual weighting section312from adaptive excitation codebook306, fixed excitation codebook308and quantization gain generation section307, respectively, and outputs an adaptive excitation vector code (A), fixed excitation vector code (F) and quantization gain code (G) showing the selection results, to multiplexing section314.

Multiplexing section314multiplexes the code (L) showing the quantized LPC outputted from LPC quantization section303, the adaptive excitation vector code (A), fixed excitation vector code (F) and quantization gain code (G) outputted from parameter determining section313and outputs the multiplexed code to low band decoding section203and encoded information integration section207as a low band component encoded information.

Next, an internal configuration of low band decoding section203shown inFIG. 2will be explained usingFIG. 4. Here, a case where low band decoding section203performs CELP type speech decoding will be explained.

Demultiplexing section401divides the low band component encoded information outputted from low band encoding section202into individual codes (L), (A), (G) and (F). The divided LPC code (L) is outputted to LPC decoding section402, the divided adaptive excitation vector code (A) is outputted to adaptive excitation codebook403, the divided quantization gain code (G) is outputted to quantization gain generation section404and the divided fixed excitation vector code (F) is outputted to fixed excitation codebook405.

LPC decoding section402decodes the quantized LPC from the code (L) outputted from demultiplexing section401, and outputs the decoded quantized LPC to synthesis filter409.

Adaptive excitation codebook403extracts one frame of samples from the past excitation specified by the adaptive excitation vector code (A) outputted from demultiplexing section401as an adaptive excitation vector and outputs the adaptive excitation vector to multiplication section406.

Quantization gain generation section404decodes the quantization adaptive excitation gain and quantization fixed excitation gain specified by the quantization gain code (G) outputted from demultiplexing section401, outputs the quantization adaptive excitation gain to multiplication section406and outputs the quantization fixed excitation gain to multiplication section407.

Fixed excitation codebook405generates a fixed excitation vector specified by the fixed excitation vector code (F) outputted from demultiplexing section401, and outputs the fixed excitation vector to multiplication section407.

Multiplication section406multiplies the adaptive excitation vector outputted from adaptive excitation codebook403by the quantization adaptive excitation gain outputted from quantization gain generation section404, and outputs the multiplication result to addition section408. Furthermore, multiplication section407multiplies the fixed excitation vector outputted from fixed excitation codebook405by the quantization fixed excitation gain outputted from quantization gain generation section404, and outputs the multiplication result to addition section408.

Addition section408adds up the adaptive excitation vector multiplied by the gain outputted from multiplication section406and the fixed excitation vector multiplied by the gain outputted from multiplication section407to generate an excitation, and outputs the excitation to synthesis filter409and adaptive excitation codebook403.

Synthesis filter409performs a filter synthesis of the excitation outputted from addition section408using the filter coefficient decoded by LPC decoding section402, and outputs the synthesized signal to post-processing section410.

Post-processing section410applies processing for improving the subjective quality of speech such as formant emphasis and pitch emphasis and processing for improving the subjective quality of stationary noise, to the signal outputted from synthesis filter409, and outputs the resulting signal to up-sampling processing section204as a low band component decoded signal.

Next, an internal configuration of high band encoding section206shown inFIG. 2will be explained usingFIG. 5. A similar-part search section501calculates the search result position tMIN(t=tMIN) by minimizing the error D between M samples of MDCT coefficients Ykof the up-sampled low band component decoded signal outputted from orthogonal transform processing section205and MDCT coefficients Xkof the input signal outputted from orthogonal transform processing section205. Similar-part search section501may also calculate the gain β at tmin. The error D and gain β can be calculated from equation 9 and equation 10, respectively.

Here,FIG. 6AandFIG. 6Bconceptually show a similar-part search by a similar-part search section501.FIG. 6Ashows an input signal spectrum, and shows the beginning part of the high band region (3.5 kHz to 7.0 kHz) of the input signal in a frame.FIG. 6Bshows a situation in which a spectrum similar to the spectrum inside the frame shown inFIG. 6Ais searched for sequentially from the beginning of the low band region of a decoded signal.

A similar-part search section501outputs MDCT coefficients Xkof the input signal, MDCT coefficients Ykof the up-sampled low band component decoded signal, and calculated search result position tMINand gain β, to amplitude ratio adjusting section502.

Amplitude ratio adjusting section502extracts the part from search result position tMINto SRbase/SRinput×(N−1) (if Xkbecomes zero in the middle, the part up the position before Xkbecomes zero), from MDCT coefficients Ykof an up-sampled low band component decoded signal, and multiplies this part by gain β and designates the resulting value as copy source spectral data Z1k, expressed by equation 11.
(Equation 11)
Z1k=Yk·β (k=tMIN, . . . , SRbase/SRinput·N−1)  [11]

Next, amplitude ratio adjusting section502generates temporary spectral data Z2kfrom copy source spectral data Z1k. To be more specific, amplitude ratio adjusting section502divides the length ((1−SRbase/SRinput)×N) of the spectral data of the high band component by the length (SRbase/SRinput×N−1−tMIN) of copy source spectral data Z1k, repeats copying the source spectral data Z1ka number of times equaling the quotient such that source spectral data Z1kcontinues from the part of k=SRbase/SRinput×N−1 of temporary spectral data Z2k, and then copies copy source spectral data Z1kfor a number of samples equaling the samples of the remainder after dividing the length ((1−SRbase/SRinput)×N) of the spectral data of the high band component by the length (SRbase/SRinput×N−1−tMIN) of copy source spectral data Z1k, from the beginning of copy source spectral data Z1k, to the tail end of temporary spectral data Z2k.

Furthermore, suppose, when Xkbecomes zero in the middle, amplitude ratio adjusting section502adds the length of the part where Xkis zero to the length ((1−SRbase/SRinput)×N) of the spectral data of the aforementioned high band component, and starts copying copy source spectral data Z1kto temporary spectral data Z2kfrom the part where Xkis zero in the middle.

Next, amplitude ratio adjusting section502adjusts the amplitude ratio of temporary spectral data Z2k. To be more specific, amplitude ratio adjusting section502divides MDCT coefficients Xkof the input signal and the high band component (k=SRbase/SRinput×N, . . . , N−1) of temporary spectral data Z2kinto a plurality of bands first.

Here, a case where temporary spectral data Z2kis copied from the part of k=SRbase/SRinput×N in the aforementioned processing, will be explained. Amplitude ratio adjusting section502calculates amplitude ratio αjfor each band as expressed by equation 12 for MDCT coefficients Xkof the input signal and the high band component of temporary spectral data Z2k. In equation 12, suppose “NUM_BAND” is the number of bands and “band_index(j)” is the minimum sample index out of the indexes making up band j.

FIG. 7shows, conceptually, the processing in amplitude ratio adjusting section502.FIG. 7shows a situation in which the spectrum of the high band region is generated based on the similar-part searched from the low band region inFIG. 6(b) (when NUM_BAND=5).

Amplitude ratio adjusting section502outputs amplitude ratio αjfor each band obtained from equation 12, search result position tMINand gain β to quantization section503.

Quantization section503quantizes amplitude ratio αjfor each band, search result position tMINand gain β outputted from amplitude ratio adjusting section502using codebooks provided in advance and outputs the index of each codebook, to encoded information integration section207as a high band component encoded information.

Here, suppose amplitude ratio αjfor each band, search result position tMINand gain β are quantized all separately and the selected codebook indexes are code_A, code_T and code_B, respectively. Furthermore, a quantization method is employed here whereby the code vector (or code) having the minimum distance (i.e. square error) to the quantization target is selected from the codebooks. However, this quantization method is in the public domain and will not be described in detail.

FIG. 8is a block diagram showing an internal configuration of decoding apparatus103shown inFIG. 1. Encoded information division section601divides the low band component encoded information and the high band component encoded information from the inputted encoded information, outputs the divided low band component encoded information to low band decoding section602, and outputs the divided high band component encoded information to high band decoding section605.

Low band decoding section602decodes the low band component encoded information outputted from encoded information division section601using a CELP type speech decoding method, to generate a low band component decoded signal and outputs the low band component decoded signal generated to up-sampling processing section603. Since the configuration of low band decoding section602is the same as that of aforementioned low band decoding section203, its detailed explanations will be omitted.

Up-sampling processing section603up-samples the sampling frequency of the low band component decoded signal outputted from low band decoding section602from SRbaseto SRinput, and outputs the up-sampled low band component decoded signal to orthogonal transform processing section604as the up-sampled low band component decoded signal.

Orthogonal transform processing section604applies orthogonal transform processing (MDCT) to the up-sampled low band component decoded signal outputted from up-sampling processing section603, calculates MDCT coefficients Y′kof the up-sampled low band component decoded signal and outputs this MDCT coefficients Y′kto high band decoding section605. The configuration of orthogonal transform processing section604is the same as that of aforementioned orthogonal transform processing section205, and therefore detailed explanations thereof will be omitted.

High band decoding section605generates a signal including the high band component from MDCT coefficients Y′kof the up-sampled low band component decoded signal outputted from orthogonal transform processing section604and the high band component encoded information outputted from encoded information division section601, and makes this the output signal.

Next, an internal configuration of high band decoding section605shown inFIG. 8will be explained usingFIG. 9. Dequantization section701dequantizes the high band component encoded information (i.e. code_A, code_T and code_B) outputted from encoded information division section601for the codebooks provided in advance, and outputs amplitude ratio αjfor each band produced, search result position tMINand gain β, to similar-part generation section702. To be more specific, the vectors and values indicated by the high band component encoded information (i.e. code_A, code_T and code_B) from each codebook are outputted to similar-part generation section702as amplitude ratio αjfor each band, search result position tMINand gain β, respectively. Here, suppose amplitude ratio αjfor each band, search result position tMINand gain β are dequantized using different codebooks as in the case of quantization section503.

Furthermore, suppose, when Y′kis zero in the middle, copy source spectral data Z1′kcovers the part from the position where k is tMINup to the position before Y′kbecomes zero, according to equation 13.

Next, similar-part generation section702generates temporary spectral data Z2′kfrom copy source spectral data Z1′kcalculated according to equation 13. To be more specific, similar-part generation section702divides the length ((1−SRbase/SRinput)×N) of the spectral data of the high band component by the length (SRbase/SRinput×N−1−tMIN) of copy source spectral data Z1′k, repeats copying copy source spectral data Z1′ka number of time equaling the quotient such that copy source spectral data Z1′kcontinues from the part of k=SRbase/SRinput×N−1 of temporary spectral data Z2′k, and then copies copy source spectral data Z1′kfor a number of samples equaling the samples of the remainder after dividing the length ((1−SRbase/SRinput)×N) of the spectral data of the high band component by the length (SRbase/SRinput×N−1−tMIN) of copy source spectral data Z1′kfrom the beginning of copy source spectral data Z1′kto the tail end of temporary spectral data Z2′k.

Furthermore, suppose, when Y′kbecomes zero in the middle, similar-part generation section702adds the length of the part where Y′kis zero, to the length ((1−SRbase/SRinput)×N) of the spectral data of the aforementioned high band component, and starts copying copy source spectral data Z1′kto temporary spectral data Z2′kfrom the part where Y′kis zero in the middle.

Next, similar-part generation section702copies the value of the low band component of Y′kto the low band component of temporary spectral data Z2′k, expressed by equation 14. Here, a case where the temporary spectral data Z2′kis copied from the part of k=SRbase/SRinput×N in the aforementioned processing, will be explained.
(Equation 14)
Z2′k=Y′k(k=0, . . . , SRbase/SRinput·N−1)  [14]

Similar-part generation section702outputs the calculated temporary spectral data Z2′kand amplitude ratio αjper band, to amplitude ratio adjusting section703.

Amplitude ratio adjusting section703calculates temporary spectral data Z3′kfrom temporary spectral data Z2′kand amplitude ratio αjfor each band outputted from similar-part generation section702, expressed by equation 15. Here, αjin equation 15 is the amplitude ratio of each band and band_index(j) is the minimum sample index in the indexes making up band j.

Amplitude ratio adjusting section703outputs temporary spectral data Z3′kcalculated according to equation 15 to orthogonal transform processing section704.

Orthogonal transform processing section704calculates decoded signal Y″nusing temporary spectral data Z3′koutputted from amplitude ratio adjusting section703, according to equation 17.

Here, Z3″kis a vector combining temporary spectral data Z3′kand buffer buf′kand is calculated according to equation 18.

Orthogonal transform processing section704obtains decoded signal Y″nas an output signal.

In this way, in accordance with Embodiment 1, to generate spectral data of the high band region of a signal to be encoded based on spectral data of the low band region of the signal, a similar-part search is performed for a part (e.g. beginning part) in the spectral data of the high band region, in the quantized low band region, and spectral data of the high band region is generated based on the search result, so that it is possible to encode spectral data of the high band region of a wideband signal based on spectral data of the low band region with an extremely small amount of information and amount of calculation processing, and, furthermore, obtain a decoded signal of high quality even when a significant quantization distortion occurs in the spectral data of the low band region.

Embodiment 1 has explained a method of performing a similar-part search with respect to MDCT coefficients of up-sampled low band component decoded signal, and the beginning part of high band components of MDCT coefficients of an input signal, and calculating parameters for generating MDCT coefficients for the high band component at the time of decoding. Now, with embodiment 2, a weighted similar-part search method will be described, whereby, in high band components of the MDCT coefficients of an input signal, lower band components are regarded more important.

Since the communication system according to Embodiment 2 is similar to the configuration of Embodiment 1 shown inFIG. 1,FIG. 1will be used, and furthermore, since the encoding apparatus according to Embodiment 2 of the present invention is similar to the configuration of Embodiment 1 shown inFIG. 2,FIG. 2will be used and overlapping explanations will be omitted. However, in the configuration shown inFIG. 2, high band encoding section206has a function different from that in Embodiment 1, and therefore high band encoding section206will be explained usingFIG. 5.

Similar-part search section501calculates a search result position tMIN(t=tMIN) when error D2between MDCT coefficients Ykof an up-sampled low band component decoded signal outputted from orthogonal transform processing section205and M (M is an integer equal to or greater than 2) samples from the beginning of MDCT coefficients Xkof the input signal outputted from orthogonal transform processing section205becomes a minimum, and gain β2at that moment. Error D2and β2are calculated according to equation 20 and equation 21, respectively.

Here, Wiin equation 20 is a weight having a value of about 0.0 to 1.0, and is multiplied when error D2(i.e. distance) is calculated. To be more specific, a smaller error sample index (that is, an MDCT coefficients of a lower band region), is assigned a greater weight. An example of Wiis shown in equation 22.

In this way, by calculating the distance using a greater weight for MDCT coefficients of lower band, it is possible to realize a search placing the emphasis on the distortion in the part connecting the low band component and the high band component.

The configurations of amplitude ratio adjusting section502and quantization section503are the same as those for the processing explained in Embodiment 1, and therefore detailed explanations thereof will be omitted.

Encoding apparatus101has been explained so far. The configuration of decoding apparatus103is the same as explained in Embodiment 1, and therefore detailed explanations thereof will be omitted.

In this way, in accordance with Embodiment 2, to generate spectral data of the high band region of a signal to be encoded based on spectral data of the low band region of the signal, the distance is calculated by assigning greater weights to smaller error sample indexes, a similar-part search for part (i.e. beginning part) of spectral data of the high band region is performed in spectral data of the quantized low band region and spectral data of the high band region is generated based on the result of the search, so that it is possible to encode spectral data of the high band region of a wideband signal in high perceptual quality based on spectral data of the low band region of the signal and furthermore obtain a decoded signal of high quality even when a significant quantization distortion occurs in the spectral data of the low band region.

The present embodiment has explained a case where, to generate spectral data of the high band region of a signal to be encoded based on spectral data of the low band region of the signal, a similar-part search for a part (i.e. beginning part) of the spectral data of the high band region is performed in the spectral data of the quantized low band region, so that the present invention is not limited to this and it is equally possible to adopt the above-described weighting in distance calculation for the entire part of the spectral data of the high band region.

Furthermore, although the present embodiment has explained a method of generating spectral data of the high band region of a signal to be encoded is generated based on spectral data of the low band region of the signal, by calculating the distance by assigning greater weights to smaller error sample indexes, performing a similar-part search for a part (i.e. beginning part) of the spectral data of the high band region in spectral data of the quantized low band region, and generating spectral data of the high band region based on the result of the search, but the present invention is by no means limited to this and may likewise adopt a method of introducing the length of copy source spectral data as an evaluation measure during a search. To be more specific, by making a search result that increases the length of the copy source spectral data, that is, by making an entry of a search position of a low band more likely to be selected, it is possible to further improve the quality of an output signal by reducing the number of discontinuous parts caused when the spectral data of the high band region is copied a plurality of times and placing the discontinuous parts in high frequency bands.

The above-described embodiments have explained that the index of the MDCT coefficients of the spectral data of the high band region generated starts from SRbase/SRinput×(N−1), but the present invention is not limited to this, and the present invention is also applicable to cases where spectral data of the high band region is generated likewise from a part where low band spectral data becomes zero, irrespective of sampling frequencies. Furthermore, the present invention is also applicable to a case where spectral data of the high band region is generated from an index specified from the user and system side.

The above-described embodiments have explained the CELP type speech encoding scheme in the low band encoding section as an example, but the present invention is not limited to this and is also applicable to cases where a down-sampled input signal is coded according to a speech/sound encoding scheme other than CELP type. The same applies to the low band decoding section.

The present invention is further applicable to a case where a signal processing program is recorded or written into a mechanically readable recording medium such as a memory, disk, tape, CD, DVD and operated, and operations and effects similar to those of the present embodiment can be obtained.

Each function block employed in the description of each of the aforementioned embodiments may typically be implemented as an LSI constituted by an integrated circuit. These may be individual chips or partially or totally contained on a single chip.

“LSI” is adopted here but this may also be referred to as “IC”, “system LSI”, “super LSI”, or “ultra LSI” depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible. After LSI manufacture, utilization of an FPGA (Field Programmable Gate Array) or a reconfigurable processor where connections and settings of circuit cells within an LSI can be reconfigured is also possible.

The disclosures of Japanese Patent Application No. 2006-131852, filed on May 10, 2006, and Japanese Patent Application No. 2007-047931, filed on Feb. 27, 2007, including the specifications, drawings and abstracts, are incorporated herein by reference in their entirety.

INDUSTRIAL APPLICABILITY

The encoding apparatus and encoding method according to the present invention make it possible to encode spectral data of the high band region of a wideband signal based on spectral data of the low band region of the signal and produce a decoded signal of high quality even when a significant quantization distortion occurs in the spectral data of the low band region, and are therefore applicable for use in, for example, a packet communication system and mobile communication system.