The Effect of Spectral Tilt on Size Discrimination of Voiced Speech Sounds

A number of studies, with either voiced or unvoiced speech, have demonstrated that a speaker’s geometric mean formant frequency (MFF) has a large effect on the perception of the speaker’s size, as would be expected. One study with unvoiced speech showed that lifting the slope of the speech spectrum by 6 dB/octave also led to a reduction in the perceived size of the speaker. This paper reports an analogous experiment to determine whether lifting the slope of the speech spectrum by 6 dB/octave affects the perception of speaker size with voiced speech (words). The results showed that voiced speech with high-frequency enhancement was perceived to arise from smaller speakers. On average, the point of subjective equality in MFF discrimination was reduced by about 5%. However, there were large individual differences; some listeners were effectively insensitive to spectral enhancement of 6 dB/octave; others showed a consistent effect of the same enhancement. The results suggest that models of speaker size perception will need to include a listener specific parameter for the effect of spectral slope.