Patent ID: 7752052

Claim:
A sound coding apparatus comprising: a first coder that performs weighting on an input signal to mask a spectrum of quantization distortion by a spectral envelope of the input signal, and thereafter encodes the input signal and obtains first coding information; a decoder that decodes the first coding information outputted from the first coder and obtains a decoded signal; a computer processor that calculates an auditory masking threshold for a decoded spectrum that is obtained from the decoded signal outputted from the decoder, generates an estimated error spectrum by calculating an equation using the decoded spectrum, compares the estimated error spectrum with the auditory masking threshold, and specifics a frequency region in the estimated error spectrum showing an amplitude equal to or greater than the auditory masking threshold; a subtracter that obtains a residual error signal of the input signal and the decoded signal; and a second coder that encodes the frequency region in the residual error signal outputted from the subtracter specified by the computer processor, and obtains second coding information, wherein: the equation is expressed as: E ′( m )= a·P ( m ) γ where E′(m) is the estimated error spectrum, P(m) is the decoded spectrum, and a and γ are constants of 0 or above and less than 1.