The role of inharmonicity on listeners’ ability to hear out voices in polyphonic music

While speech perception amidst competing talkers is well-studied, the perception of polyphonic music remains less explored. Pitch differences aid in source segregation, yet reductions in harmonicity have relatively little effect on speech intelligibility in such conditions. We hypothesized that source identification and segregation in music would rely more on harmonicity, given the central role of pitch in music and fewer alternative segregation cues, such as temporal incoherence. Polyphonic vocal passages from a female singer were generated from four-second MIDI excerpts. Inharmonic versions were created by introducing random frequency deviations within the first 30 harmonics of each note. Two main experiments were conducted: Experiment 1 involved participants estimating the number of voices in passages with one to five simultaneous voices; Experiment 2 involved participants attending to one voice within a two- to five-voice passage and reporting whether a final probe tone matched the pitch of the last note in the attended voice. Both experiments varied the degree of inharmonicity. Performance decreased with increasing inharmonicity and voice count, though participants remained above chance in all conditions. The results confirm the importance of harmonicity in source segregation within music but suggest that some segregation ability remains even when harmonicity is severely degraded.