MASKING BY MODULATED AND UNMODULATED NOISE - EFFECTS OF BANDWIDTH, MODULATION RATE, SIGNAL FREQUENCY, AND MASKER LEVEL

The threshold for a sinusoidal signal masked by a band of noise is oft en times lower when the masking noise is modulated than when it is unm odulated. The difference in masked thresholds is referred to as the mo dulated-unmodulated difference, or MUD. These present experiments exam ined the effects of masker bandwidth, masker rate, and masker level on the MUD at several different signal frequencies. The MUD generally in creased with increasing masker bandwidth; for masker bandwidths wider than a critical band (or an equivalent rectangular bandwidth-ERB), the results may be influenced by across-channel processes underlying como dulation masking release. The MUD for an ERB masker (MUD(ERB)) was inf luenced less by masker rate than was the MUD for a broadband (BB) mask er (MUD(BB)). The MUD(ERB) and especially the MUD(BB) increased signif icantly with increasing masker level when the modulated masker was mod ulated at a depth (m) of 1.0, but not when it was modulated at a depth of 0.75. These results have significant implications for extending th e MUD paradigm to hearing-impaired subjects. Finally, the MUD(ERB) and the MUD(BB) increased with increasing signal frequency. This effect f or the ERB masker is largely (if not completely) due to the wider abso lute bandwidths at higher frequencies. The effect with the BE masker m ay be influenced by differences in the magnitude of suppression across frequency. (C) 1997 Acoustical Society of America.