The coupling of sub‐audio amplitude and frequency modulafions and the perception of spectral envelope characteristics

Abstract

One possible cue for the relative perceptual invariance of a resonant source with pitch change is the tracing of its spectral envelope by its modulating frequency components. This tracing would reduce the ambiguity concerning the resonant structure of the source at higher F0's where the formants are not filled by partials. This paper investigates the role that spectral tracing (FM‐induced AM) plays in the perception and identification of vowels with high F0. Two five‐formant vocal spectra were selected to give nearly identical spectra when not modulated. When modulated by vibrato, a single component differed in the sign of its amplitude‐frequency slope while the behavior of the rest was identical in the two cases. At larger frequency modulation depths, a difference in vowel quality is perceived. The threshold depth at which the stimuli were distinguished and the threshold depth for identification were determined. Discrimination thresholds were lower than identification thresholds. The discrimination thresholds for sine tones with amp‐freq slopes of opposite sign were also determined, and were found to be greater than the thresholds for the complex tones. The results will be discussed in terms of intensity discrimination results and of recent work in spectral profile analysis.