The effect of frequency lowering on consonant discrimination
C. M. Reed, Bruce L. Hicks, Louis D. Braida, N. I. Durlach · The Journal of the Acoustical Society of America · 1978
We have investigated the basic discriminability of consonants that were processed using pitch-invariant frequency lowering with either uniform (linear) or nonuniform (warped) compression of the frequency axis. The bandwidth of the unprocessed signal was compressed by factors of two and four to achieve bandwidths of 2500 and 1250 Hz, respectively. For each of the lowering factors, five warping characteristics were studied in addition to lowpass filtering to the equivalent bandwidth. Stimuli were CV syllables made up of 24 consonants and three vowels, recorded by two male and two female speakers. Discrimination tests were performed using an AB-BA procedure. As expected, performance for the 2500-Hz bandwidth was superior to that for the 1250-Hz bandwidth. Overall performance with the best lowering-warping combination was roughly comparable to that with lowpass filtering for the same bandwidth; however, the patterns of performance over articulatory features were significantly different. In general, lowering-warping performance was superior to filtering performance for contrasts of fricative sounds but inferior for contrasts of nasals and semi-vowels.[Work supported by NIH.]