Noise shaping filter design for minimally audible signal requantization

Signal requantization to reduce the word-length of an audio stream introduces distortions. Noise shaping can be applied in combination with a psychoacoustic model in order to make requantization distortions minimally audible. The psychoacoustically optimal noise shaping curve depends on the time-varying characteristics of the input signal. Therefore, the noise shaping filter coefficients are to be computed and updated on a regular basis. We show that the optimal coefficients can be obtained by solving a simple least squares problem. Thus, an efficient scheme for minimally audible requantization can be proposed in which the noise shaping coefficients are computed from the psychoacoustic masking curve by solving a linear matrix equation