Discrimination of Minimum- and Maximum-Phase Waveforms

Abstract

Observers were asked to discriminate between a pair of computer-synthesized waveforms having identical long-time energy spectra but different short-time spectra. One member of the pair was constructed by passing a time waveform, called an excitation function, through a simple resonant circuit. We call this waveform “minimum phase.” “Maximum-phase” waveforms were constructed by passing the same excitation function through a filter whose impulse response is reversed in time. The pairs of signals thus generated have identical energy spectra but differ in their phase spectra. Within the duration of the impulse response, the effect of time-reversing the impulse response is to produce what is called local time reversals in the output waveform. Three excitation waveforms were used: a noise burst, a sinusoid, and a pulse. The effects of duration of the impulse response and bandwidth of the filter were examined. In agreement with phase discrimination of transients, observers can discriminate local time reversals within sustained stimuli down to about 2 msec. For a given excitation function, the discrimination was maintained so long as the bandwidth of the filter was between 250 Hz and 30 Hz. [Research supported by the National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare.]