Decoder, encoder, and methods thereof

A coding apparatus comprising:

• a first coding section that encodes an input signal through speech coding to generate a first code and performs an orthogonal transformation on a signal obtained by decoding the first code, to generate a first spectrum;
• a spectrum generating section that performs the orthogonal transformation on the input signal to generate a second spectrum;
• a band selection section that divides a frequency band into a plurality of bands, selects a preset number of bands based on an energy of a residual signal between the first spectrum and the second spectrum, generates band selection information indicating information about the selected band, outputs a spectrum of the selected band in the first spectrum as a first selected spectrum, and outputs a spectrum of the selected band in the second spectrum as a second selected spectrum;
• a suppressing section that suppresses an amplitude of the first selected spectrum using a suppressing coefficient representing the degree of suppression, to generate a suppressed spectrum;
• a residual spectrum calculating section that calculates a difference between the second selected spectrum and the suppressed spectrum to generate a residual spectrum;
• a second coding section that encodes the residual spectrum through music coding to generate a second code, and decodes the second code to generate a decoded residual spectrum;
• a decoded spectrum generating section that generates a decoded spectrum using the suppressed spectrum and the decoded residual spectrum;
• and
• a distortion evaluating section that calculates distortion between the second selected spectrum and the decoded spectrum and searches for the suppressing coefficient which minimizes the distortion.

A decoding method that receives and decodes first coded data generated through speech coding and second coded data generated through music coding, the method comprising:

• a first decoding step of performing an orthogonal transformation on a signal obtained by decoding the first coded data, to generate a first spectrum;
• a second decoding step of decoding the second coded data to generate a second spectrum;
• an identification step of identifying a first band in which a degree of suppression of an amplitude of the first spectrum is adjusted, using the second spectrum;
• and
• a suppressing step of suppressing an amplitude of the first band of the first spectrum based on the adjusted degree.

A coding method comprising:

• a first coding step of encoding an input signal through speech coding to generate a first code and performing an orthogonal transformation on a signal obtained by decoding the first code to generate a first spectrum;
• a spectrum generating step of performing the orthogonal transformation on the input signal to generate a second spectrum;
• a band selection step of dividing a frequency band into a plurality of bands, selecting a preset number of bands based on an energy of a residual signal between the first spectrum and the second spectrum, generating band selection information indicating information about the selected band, outputting a spectrum of the selected band in the first spectrum as a first selected spectrum, and outputting a spectrum of the selected band in the second spectrum as a second selected spectrum;
• a suppressing step of suppressing an amplitude of the first selected spectrum using a suppressing coefficient representing the degree of suppression, to generate a suppressed spectrum;
• a residual spectrum calculating step of calculating a difference between the second selected spectrum and the suppressed spectrum to generate a residual spectrum;
• a second coding step of encoding the residual spectrum through music coding to generate a second code, and decoding the second code to generate a decoded residual spectrum;
• a decoded spectrum generating step of generating a decoded spectrum using the suppressed spectrum and the decoded residual spectrum;
• and
• a distortion evaluating step of calculating distortion between the second selected spectrum and the decoded spectrum and searching for the suppressing coefficient which minimizes the distortion.