Some physical and psychological effects produced by selective delays of the envelope of narrow bands of noise.

One can construct narrow bands of noise that contain delays of either the envelope, the phase, or the carrier separately or in combination. Delayed and undelayed noises will have identical spectra if, and only if, both the envelope and the phase undergo delays of the same magnitude. To study lateralization of these signals, an acoustic pointing task was employed in which listeners varied the interaural intensitive disparity of a narrow band of noise (the pointer) so that it matched the position of a second, experimenter-controlled stimulus (the target) which contained symmetric interaural delays of only the envelope. Targets were narrow bands of noise with center frequencies chosen at octave intervals between about 500 Hz and about 4000 Hz. The smallest bandwidth was 100 Hz and the largest was 800 Hz. For high-frequency stimuli, delays of only the envelope of a narrow band of noise appear to mediate lateralization which is greatest for bands centered near 2000 Hz. For low frequencies, delays larger than 800 microseconds were required to produce acoustic images appreciably away from the midline. These findings confirm the notion that listeners are sensitive to interaural temporal disparities in the envelopes of high-frequency, complex stimuli.