Patent ID: 7930185

Claim:
An apparatus for encoding an audio signal, comprising: an acoustic analyzer that analyzes the audio signal to calculate perceptual entropy indicating how many bits are required for quantization; a coded bit count monitor that monitors the number of coded bits produced from the audio signal and calculates the number of available bits for a current frame; a frame division number determiner that determines a division number N for dividing a frame of the audio signal into N blocks, based on a combination of the perceptual entropy and the number of available bits, such that the N blocks will have lengths suitable for suppressing sound quality degradation due to pre-echoes and bit starvation; an orthogonal transform processor that divides the frame by the determined division number and subjects each divided block of the audio signal to an orthogonal transform process, thereby obtaining orthogonal transform coefficients; and a quantizer that quantizes the orthogonal transform coefficients on a divided block basis; wherein: the frame division number determiner comprises a conversion map defining the division number with respect to the perceptual entropy and the number of available bits; the conversion map gives a larger division number for a larger perceptual entropy, so that the resulting blocks will have shorter lengths suitable for suppressing pre-echoes and consequent degradation of sound quality; and the conversion map gives a smaller division number for a smaller number of available bits, so that the resulting blocks will have longer lengths suitable for suppressing bit starvation and consequent degradation of sound quality.