Comodulation masking release for various monaural and binaural combinations of the signal, on-frequency, and flanking bands.

Abstract

The threshold for a signal masked by a narrow band of noise centered at the signal frequency (the on-frequency band) may be reduced by adding to the masker a second band of noise (the flanking band) whose envelope is correlated with that of the first band. This effect is called comodulation masking release (CMR). These experiments examine two questions. (1) How does the CMR vary with the number and ear of presentation of the flanking band(s)? (2) Is it possible to obtain a CMR when a binaural masking level difference (BMLD) is already present, and vice versa? Thresholds were measured for a 400-ms signal in a continuous 25-Hz-wide noise centered at signal frequencies (fs) of 250, 1000, and 4000 Hz. This masker was presented either alone or with one or more continuous flanking bands whose envelopes were either correlated or uncorrelated with that of the on-frequency band; their frequencies ranged from 0.5fs to 1.5fs. CMRs were measured for six conditions in which the signal, the on-frequency band, and the flanking band(s) were presented in various monaural and binaural combinations. When a single flanking band was used, the CMR was typically around 2-3 dB. The CMR increased to 5-6 dB if an additional flanking band was added. The effect of the additional band was similar whether it was in the same ear as the original band or in the opposite ear. At the lowest signal frequency, a large CMR was observed in addition to a BMLD and vice versa. At the highest signal frequency, the extra release from masking was small. The results are interpreted in terms of the cues producing the CMR and the BMLD.