Release from masking caused by envelope fluctuations.

This paper examines how short-term energy fluctuations in a masker affect the thresholds for tones at frequencies above those of the masker. Two equally intense tones at 1060 and 1075 Hz produce up to 25 dB less masking than does a 1075-Hz tone set to the overall level of the two-tone complex. At wider frequency separations, two-tone complexes also produce less masking than the pure tone. These results indicate that envelope fluctuations in a masker, whose spectrum is confined to a single critical band, may result in release from masking. The release from masking probably is related to the comodulation masking release reported by Hall et al. [J. Acoust. Soc. Am. 76, 50-56 (1984b)] for modulated-noise maskers with bandwidths greater than one critical band. Further measurements with maskers, whose intensity level in the critical band around 1 kHz was 90 dB SPL, show similar masking by a pure tone and a 625- to 1075-Hz bandpass noise, but less masking by narrow-band noises. These results are inconsistent with a simple frequency selective energy-detector model and indicate that the auditory system can use periods of low masker energy as brief as a few ms to enhance detection of a tone. The results also imply that the upward spread of excitation is best represented by masking patterns for noises with bandwidths of several critical bands.