Psychoacoustically Optimal Sigma-Delta Modulation (P)
A psychoacoustically optimal sigma-delta modulator (SDM) possesses a noise 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 dither, the noise floor can be made minimally audible by forcing the noise-shaping characteristic to follow the threshold of hearing. Such an action is possible by appropriate control of noise-shaping zero locations, and has the benefit of increasing the perceived resolution of a given modulator design. Alternatively, for a given perceived resolution, psychoacoustically optimal zero locations allow a reduction in oversampling factor or modulator order, or both. Optimal zero locations and associated enhancements in perceived resolution are determined for SDM orders ranging between 1 and 8.
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