The Role of FM-induced AM in Dynamic Spectral Profile Analysis

(1) Recent work by Green and colleagues (cf. [Green, 1983]) has begun to demonstrate with psychophysical methods that the human auditory system is capable of extracting a global representation of the spectral envelope of a signal. This may serve to identify the resonance structure characteristics of a sound source. However, this previous work has been exclusively confined to relatively dense steady-state, inharmonic stimuli of simple spectral forms (a single bump in the spectral profile). Dynamic stimuli, those with frequency jitter or vibrato, might be helpful in reducing perceptual ambiguity in cases where there are not enough partials present in a sound to clearly define a spectral envelope. They may do this by tracing out the spectral envelope through time, thus increasing information about the resonance structure. (2) While this seems intuitively obvious, previous work on high-pitched vowel identification in the presence of frequency vibrato has yielded ambiguous results ([Sundberg, 1977]). These researchers claim that intonation contours or vibrato had slight, or even detrimental, effects on vowel identification. The present study demonstrates, to the contrary, that if the amplitude behavior of a given partial is coupled with its frequency behavior according to a given spectral envelope, this information can be used by the auditory system to discriminate and identify the vowel quality or timbre of complex harmonic sounds.