Effect of multiple compression channels on vowel spectra

Abstract

Multichannel wide-dynamic range compression (MCC) is a common amplification strategy, but whether using more channels provides an advantage for speech recognition is disputed. Some researchers have hypothesized that MCC with a large number of compression channels can reduce spectral contrast and degrade recognition, but this has not been empirically tested. A detailed acoustic analysis was undertaken to determine (1) whether vowel spectra are altered by multichannel compression relative to single-channel compression, and (2) to quantify changes to vowel spectra as a function of the number of compression channels. Stimuli were eight naturally spoken vowels produced by five males and five females in an /hVd/ context. A series of compression conditions (1 through 16 channels) was created using clinically representative parameters. After compression processing, F1, F2, and F3 were measured using spectrograms, LPC, and FFT analysis. A quantitative measure was developed to represent spectral changes after compression. Preliminary data show spectral smoothing with more than four channels. Smaller numbers of compression channels have minimal effects on vowel spectra. These data will be related to vowel recognition scores.