Decoder, encoder, and methods thereof
View Patent ↗Disclosed is a decoder capable of improving the sound quality of a decoded sound signal in an encoding method which combines speech encoding and music encoding in a hierarchical structure. A transform-encoding decoding unit ( 202 ) decodes transform-encoded data to generate a spectrum of a decoded transform-encoded signal. A band decision unit ( 203 ) uses the spectrum of the decoded transform-encoded signal to decide whether each of a plurality of bands in which frequency components of an input signal are divided constitute a first band in which a transform encoded pulse is not established or a second band in which said pulse is established. A CELP component suppression unit ( 207 ) suppresses the spectrum of a CELP decoded signal, which is the frequency component of a decoded signal of CELP encoded data, to the extent that suppression in the first band is weaker than suppression in the second band.
1. A decoding apparatus that receives and decodes CELP coded data generated through CELP coding and transform coded data generated through transform coding, the apparatus comprising:
a memory that stores instructions;
a processor that executes the instructions;
a CELP decoder that decodes the CELP coded data;
a first transformer that performs a modified discrete cosine transform on the decoded CELP coded data, to generate a first spectrum;
a transform coding decoder that decodes the transform coded data to generate a second spectrum;
an identification section that determines that one of a plurality of bands obtained by dividing frequency components of the second spectrum is a first band in which no pulse is generated by the transform coding and another of the plurality of bands is a second band next to the first band in which pulses are generated by the transform coding, using the second spectrum, and identifies degrees of a CELP suppression of an amplitude of the first spectrum for the first band and the second band based on the determination result;
a suppressor that suppresses an amplitude of the first band of the first spectrum and an amplitude of the second band of the first spectrum, based on the identified degrees of the CELP suppression of the amplitude of the first spectrum, and outputs a CELP component suppressed spectrum,
an adder that adds the CELP component suppressed spectrum and the second spectrum to calculate a decoded signal spectrum; and
a second transformer that performs an inverse modified discrete cosine transform on the decoded signal spectrum, and outputs a decoded signal that is a speech/audio signal, wherein
the degree of the suppression in the first band is a lower level than that in the second band,
the identification section further determines whether a band determined to be the second band among the plurality of bands is a third band having a high pulse density or a fourth band having a low pulse density,
the suppressor suppresses the first spectrum in the third band at a degree equal to or higher than suppression in the fourth band and suppresses the first spectrum in the first band at a degree lower than suppression in the fourth band,
the suppressor suppresses the first spectrum at a frequency in which the pulses are not generated in the third band, at a degree higher than suppression in the fourth band, suppresses the first spectrum at a frequency in which the pulses are generated in the third band at the same degree as suppression in the fourth band, and
at least one of the CELP decoder, the first transformer, the transform coding decoder, the identification section, the suppressor, the adder and the second transformer is implemented by the processor.
2. The decoding apparatus according to claim 1 , further comprising:
an adjusting section that adjusts a suppressing coefficient indicating the degree of suppression to the first spectrum, a value of the suppressing coefficient decreasing with an increase in the degree of the suppression, and adjusts the suppressing coefficient in the first band to a higher level than the suppressing coefficient in the second band, wherein the suppressing section suppresses the first spectrum by multiplying the first spectrum by the suppressing coefficient.
3. The decoding apparatus according to claim 1 further comprising:
an adjusting section that adjusts a suppressing coefficient indicating the degree of suppression to the first spectrum, a value of the suppressing coefficient decreasing with an increase in the degree of the suppressing, and adjusts the suppressing coefficient in the third band to a lower level than the suppressing coefficient in the fourth band and adjusts the suppressing coefficient in the first band to a higher level than the suppressing coefficient in the fourth band, wherein the suppressing section suppresses the first spectrum by multiplying the first spectrum by the suppressing coefficient.
4. The decoding apparatus according to claim 1 , wherein:
the transform coding decoder comprises a third decoder that decodes the transform coded data to generate a selected spectrum, and
the decoding apparatus further comprises a band restoring section that receives band selection information indicating a band subjected to the transform coding upon the generation of the transform coded data and generates the second spectrum using the band selection information and the selected spectrum; and
the identification section identifies the first band further using the band selection information.
5. A decoding method that receives and decodes CELP coded data generated through CELP coding and transform coded data generated through transform coding, the method comprising:
decoding the CELP coded data;
performing a modified discrete cosine transform on the decoded CELP coded data, to generate a first spectrum;
decoding the transform coded data to generate a second spectrum;
determining that one of a plurality of bands obtained by dividing frequency components of the second spectrum is a first band in which no pulse is generated by the transform coding and another of the plurality of bands is a second band next to the first band in which pulses are generated by the transform coding, using the second spectrum;
identifying degrees of a CELP suppression of an amplitude of the first spectrum for the first band and the second band based on the determination result;
suppressing an amplitude of the first band of the first spectrum and an amplitude of the second band of the first spectrum, based on the identified degrees of the CELP suppression of the amplitude of the first spectrum and outputting a CELP component suppressed spectrum;
adding the CELP component suppressed spectrum and the second spectrum to calculate a decoded signal spectrum; and
performing an inverse modified discrete cosine transform on the decoded signal spectrum, and outputting a decoded signal that is a speech/audio signal,
wherein the degree of the suppression in the first band is a lower level than that in the second band, wherein
the identifying includes determining whether a band determined to be the second band among the plurality of bands is a third band having a high pulse density or a fourth band having a low pulse density; and
in the suppressing, the first spectrum in the third band is suppressed at a degree equal to or higher than suppression in the fourth band, and the first spectrum in the first band is suppressed at a degree lower than suppression in the fourth band,
in the suppressing, the first spectrum at a frequency in which the pulses are not generated in the third band is suppressed at a higher degree than suppression in the fourth band, and the first spectrum at a frequency in which the pulses are generated in the third band is suppressed at the same degree as suppression in the fourth band, and
at least one of the decoding the CELP coded data, the performing the modified discrete cosine transform, the decoding the transform coded data, the determining, the identifying, the suppressing, the adding and the performing the inverse modified discrete cosine transform is performed by a processor of an apparatus that includes a memory that stores instructions and the processor which executes the instructions.