Patent ID: 6941333

Claim:
A digital signal processing apparatus for converting a first digital signal having a sampling frequency of fs (Hz) and a plurality of bits as quantization bits into a second digital signal having a sampling frequency of m×n×fs and one bit as a quantization bit wherein m and n are positive integers larger or equal to two, said digital signal processing apparatus comprising: frequency analyzing means for subjecting said first digital signal inputted thereto to frequency analysis processing; first noise level calculating means for calculating an average noise level of a predetermined range of said first digital signal based on a result of the frequency analysis obtained by said frequency analyzing means; dither generating means for generating a dither signal of high frequencies beyond the audible range; second noise level calculating means for calculating a noise level of the dither signal generated by said dither generating means; normalizing means for normalizing the noise level calculated by said second noise level calculating means based on the average noise level calculated by said first noise level calculating means; first oversampling means for oversampling said first digital signal at a sampling frequency of m (m is the positive integer ≧2)×fs (Hz); adding means for adding the multi-bit digital signal oversampled by said first oversampling means to the dither signal having a noise level normalized by said normalizing means; second oversampling means for oversampling an addition output of said adding means at a sampling frequency of n (n is the positive integer ≧2)×fs (Hz); and delta-sum modulating means for converting a multi-bit digital signal oversampled by said second oversampling means into a 1-bit digital signal.