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.