On the audibility of all-pass phase in electroacoustical transfer functions

Audible effects of second-order all-pass sections with center frequencies in the range of 1-12 kHz were studied in headphone listening experiments. All-pass sections give rise to two effects. 1) A perception of "ringing" or "pitchiness," which is related to an exponentially decaying sinusoid in the impulse response of all-pass sections with high Q factors. The ringing is especially audible for impulsive sounds, whereas it is often masked with everyday sounds such as speech and music. With an impulse signal the ringing was found to be audible when the decay time constant for the sinusoid exceeds approximately 0.8 ms (peak group delay of 1.6 ms), independent of the center frequency within the frequency range studied. 2) A lateral shift of the auditory image, which occurs when an all-pass section is inserted in the signal path to only one ear. The shift is related to the low-frequency phase and group delays of the all-pass section, and it was found to be audible whenever t hese exceed approximately 35 s, independent of the signal.