The influence of amplitude modulation depth on perceived roughness of vowels

Abstract

Previous research has shown that roughness perception for vowels is influenced by the waveform amplitude modulation. It was observed that sinusoidal modulation (constant modulation depth of 100%) between 20 Hz and 70 Hz has the greatest impact on perceived roughness of vowels [Shrivastav & Eddins, 2011; JASA, 129, 2661]. The present experiment examined the effects of modulation depth on the perception of roughness for two of 10 vowels used by Shrivastav & Eddins (2011). Synthetic copies of two vowel stimuli selected from the Sataloff/Heman-Ackah database were generated using a Klatt synthesizer. Sinusoidal amplitude modulation was superimposed on each vowel using three modulation frequencies (20 Hz, 30 Hz, and 45 Hz) and five modulation depths (0, -5, -10, -15, and -20 dB). Listeners judged the perceived roughness of each of the 30 speech stimuli (2 talkers x 3 modulation frequencies X 5 modulation depths) by matching it to a comparison sound. The comparison sound consisted of a sawtooth wave, mixed with speech-shaped noise, and amplitude modulated with a raised (power of 4) cosine wave. Results will show how depth of amplitude modulation affects perceived roughness and will help to develop predictive models to quantify roughness. Research funded by NIH.