Reference Signal for Signal Quality Studies

A family of reference signals for signal quality studies is described that is perceptually similar to speech signals undergoing certain signal-dependent distortions, such as quantizing and predictive coding. This perceptual similarity can yield greater accuracy and reproducibility in subjective comparison tests than do reference signals employing additive, signal-independent noises. Equally important, for nonstationary and the intermittent signals (such as speech) the signal-to-noise (S/N) ratios of the reference signals described here are defined on an instantaneous (sample-by-sample) basis, thus avoiding the troublesome ambiguities in measuring signal and noise powers. The distorted signal whose quality is to be evaluated can be assigned an equivalent S/N ratio independent of the time intervals over which average are extended.