PSYCHOACOUSTICALLY OPTIMAL SIGMA-DELTA MODULATION

A psychoacoustically optimal sigma-delta modulator (SDM) possesses a n oise floor with a power spectral density that is invariant with input signal characteristics, and which is also minimally audible. While SDM idle tones and noise modulation can be efficiently eliminated using d ither, the noise floor can be made minimally audible by forcing the no ise-shaping characteristic to follow the threshold of hearing. Such an action is possible by appropriate control of noise-shaping zero locat ions, and has the benefit of increasing the perceived resolution of a given modulator design. Alternatively, for a given perceived resolutio n, psychoacoustically optimal zero locations allow a reduction in over sampling factor or medulator order, or both. Optimal zero locations an d associated enhancements in perceived resolution are determined for S DM orders ranging between 1 and 8.