[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

About importance of "phase" in sound recognition: Helmholtz experiment

For those interested in the random phase (RPH) - cosine phase (CPH) discrimination in multi-harmonic tones,
I replicated and extended the phase experiment that Helmholtz reports in his book comparing random phase and cosine phase waves some years ago.
The results are presented in Section I (pg 1562) of

Patterson, R.D. (1987b). A pulse ribbon model of monaural phase perception. J. Acoust. Soc. Am., 82, 1560-1586.
The conclusion was that the general discrimination between RPH and CPH waves is possible over a wide range of repetition rates, bandwidths and spectral locations. The text of the relevant section in the paper is below, and section I of the paper lists the other, earlier reports on the topic.

Listeners were presented with a CPH wave and an RPH wave in a two- interval, forced-choice experiment (2IFC), and were required to choose the RPH wave. The waves had identical power spectra composed of 31 equal-amplitude harmonics. A detailed description of the procedure and stimulus conditions is presented in Sec. III B. Three listeners immediately achieved 100% performance in this task when the repetition rate was
62.5, 125, or 250 cps. Performance fell off over the next octave and was below 75% at 500 cps. Subsequently, two bands of noise were introduced to mask most of the signal components and leave the listener with a section that was only eight harmonics wide. The lowest audible harmonic was the fourth, the eighth, or the sixteenth. The timbre difference was more obvious for stimuli with high harmonics; nevertheless, all three listeners achieved virtually perfect performance no matter where the eight harmonics occurred in the spectrum, provided the repetition rate of the wave was 250 cps or lower. Finally, the noise bands were positioned so that the listener could hear only four adjacent harmonics, again with the lowest being harmonic 4, 8, or 16. At 62.5 and 125 cps, the timbre difference was still audible; at 250 cps, performance fell off as the position of the lowest harmonic decreased from 8 to 4. Thus the general discrimination between RPH and CPH waves is possible over a wide range of repetition rates and spectral locations.

Regards Roy P
Roy Patterson
Centre for the Neural Basis of Hearing
Department of Physiology, Development and Neuroscience
University of Cambridge, Downing Street, Cambridge, CB2 3EG
  phone     +44 (1223) 333819    fax 333840
  email:        rdp1@xxxxxxxxx