Masked threshold difference due to masker harmonicity: Uniform modulation rates of auditory filter outputs versus periodicity in waveform fine structure

In a previous paper [Treurniet and Boucher, J. Acoust. Soc. Am. 109, 306-32 0 (2001)], a model was presented which successfully accounted for the lower threshold obtained using a harmonic masker instead of a similar inharmonic masker. For the harmonic masker, the frequencies of partials were equally spaced, so the envelope modulation rates of auditory filter outputs were in variant across filters. However, for the inharmonic masker, the intervals b etween adjacent partials were not equal and this resulted in a decreased un iformity of modulation rates across filters. The model proposed that the lo wer uniformity interferes with detection of a probe-induced change in the m odulation rates, thus accounting for the masked threshold difference. This paper shows that an inharmonic masker yields thresholds similar to a harmon ic masker provided that the modulation rates are uniform across the auditor y filters involved in processing the masker and probe. Thus, the lowered th reshold associated with a harmonic masker appears to arise from uniform mod ulation rates across auditory filters, and does not require periodicity in the fine structure of the waveform produced by partial frequencies that are integer multiples of a fundamental. (C) 2001 Acoustical Society of America .