Fundamental Frequency and the Intelligibility of Competing Voices

When two people speak at the same time, it is easier to understand what either of them is saying if the voices differ in fundamental frequency (F0). The contribution of F0 to the intelligibility of pairs of simultaneous sentences was investigated using a high-quality speech vocoder. Word identification accuracy improved by 23% as the F0 difference between the voices increased from 0 to 8 semitones. With a 4-semitone difference, benefits of F0 were asymmetrical: the sentence with the higher F0 was more intelligible. F0 differences provided similar gains when F0 was held constant using a monotone pitch, and when the natural pattern of F0 variation was preserved in each sentence. Time-varying F0 did not result in improved identification compared to constant F0, except at 0 and 1 semitones where marginal improvements could be attributed to perceptual segregation based on momentary differences in static F0, rather than F0 dynamics.