Voice Pitch Rate Patterns on an Analog Ear
John L. Stewart · The Journal of the Acoustical Society of America · 1970
In response to stimulation by a voiced speech sound, a point on the basilar membrane of an electric analog cochlea executes motions in the manner of a comparatively high-frequency carrier with envelope fluctuations at the fundamental voice pitch rate and/or at the second or third harmonic of this rate. Perception of a sound is based collectively on the pattern of such motions over the entire cochlea. These motions have been observed and photographed using a two-dimensional oscilloscope display wherein distance along the cochlea is one dimension, time is another (2 msec/cm). and light spot intensity represents magnitude. A form of inhibiting detection was used to improve contrast and achieve amplitude range compression. Patterns for a number of different speech sounds as produced by several different speakers are presented and discussed. Some pattern features appear to relate mostly to the sound and others to the speaker. Localization along the cochlea is not as important as is the general pattern arrangement. Speech sounds synthesized by pattern matching retain some quality characteristics; and synthesis permits pattern features of little importance to be identified by experiment. The analog cochlea reveals comparatively high-speed envelope fluctuations, even in parts of the cochlea responsive to frequencies below 1 kHz; comparable patterns are not readily obtained from a spectrum analyzer because of limited channel bandwidths, especially at low frequencies.