Effect of masker harmonicity on threshold: Auditory filter envelope-modulation rate variability versus equidistant spacing of partial frequencies

Abstract

In a previous paper [W. C. Treurniet and D. R. Boucher, J. Acoust. Soc. Am. 109, 306–320 (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 separated by a fixed amount, so the envelope modulation-rates of auditory filter outputs remained the same across filters. However, for the inharmonic masker, the interval between adjacent partials was not fixed and this resulted in a decreased uniformity of modulation-rates across filters. The model proposed that the lower uniformity impedes detection of a probe-induced change in the modulation rates, thus accounting for the masked threshold difference. This paper shows that an inharmonic masker yields results similar to a harmonic masker provided that the modulation rates are uniform across affected auditory filters. Thus, the lowered threshold associated with a harmonic masker appears to arise from invariant modulation-rates across auditory filters, and does not require that all partial-frequencies be integer multiples of a fundamental.