A comparison of modulation indices for describing amplitude-compressed speech.
Pamela E. Souza, Frederick J. Gallun, Eric C. Hoover · The Journal of the Acoustical Society of America · 2009
This presentation explores two approaches to characterizing changes to speech with amplitude-compression amplification. In the first, we considered changes to waveform morphology using the envelope difference index (EDI); [Fortune et al. (1994)] to quantify the effects on amplitude envelope in the time domain. In the second, the spectral correlation index (SCI); [Gallun & Souza (2008)] was used to compare signal envelopes in the frequency domain. In the SCI, similarity is represented by the correlation of the average modulation spectra at six octave-spaced amplitude modulation frequencies (1–32 Hz) in six octave-spaced carrier frequency regions (250–8000 Hz) for a pair of phonemes. Test stimuli were a set of 16 vowel-consonant-vowel (VCV) syllables spoken by four talkers. The VCVs were digitally processed to limit spectral information using a signal-correlated noise technique [Schroeder (1968)] then submitted to a compression amplification simulation in which parameters (compression ratio and release time) were selected to achieve a range of temporal alteration. Consonant identification scores for 10 normal-hearing listeners were obtained and related to the modulation indices. Although the SCI was more sensitive to changes in specific compression parameters, the EDI was more closely related to recognition. [Work supported by R01 DC0060014 and VA RR&D CDA-2 C4963W.]