Roles of the target and masker fundamental frequencies in voice segregation

Intelligibility of a target voice improves when its fundamental frequency (F0) differs from that of a masking voice, but it remains unclear how this masking release (MR) depends on the two relative F0s. Three experiments measured speech reception thresholds (SRTs) for a target voice against different maskers. Experiment 1 evaluated the influence of target F0 itself. SRTs against white noise were elevated by at least 2 dB for a monotonized target voice compared with the unprocessed voice, but SRTs differed little for F0s between 50 and 150 Hz. In experiments 2 and 3, a MR occurred when there was a steady difference in F0 between the target voice and a stationary speech-shaped harmonic complex or a babble. However, this MR was considerably larger when the F0 of the masker was 11 semitones above the target F0 than when it was 11 semitones below. In contrast, for a fixed masker F0, the MR was similar whether the target F0 was above or below. The dependency of these MRs on the masker F0 suggests that a spectral mechanism such as glimpsing in between resolved masker partials may account for an important part of this phenomenon.