Vowel perception at high F0 in real and synthetic speech

It is known that vowels are less intelligible at higher pitches, but it remains unclear whether this is solely driven by talkers’ articulation or by changes in the acoustic structure. This study disentangles these factors to understand the production–perception mapping mechanism for higher pitched vowels. 102 participants completed a word identification task. They listened to recordings of bVt spanning 51 semitones (C2-D6), and identified the word given five choices (beat, boot, bet, bot, bat). Half the participants listened to sung vowels by four opera singers (Soprano, Mezzo-Soprano, Tenor, Baritone), and their half listened to Klattgrid synthesized vowels with two sets of fixed formant values (man, woman) across the same F0 ranges as the singers. Results show identification rates declining as F0 approaches F1, with rates for sung vowels beginning to decline at lower pitches than for synthesized vowels. The effect of F0 also varies by vowel; mid-front vowels AE and EH are confusable across both conditions, and IY remains near-ceiling in synthesized but not sung conditions across the F0 range. Overall results suggest that the decline of vowel intelligibility at high pitches is contributed both by talkers’ pitch-dependent vocal tract adjustments and by the changes in the spectrum itself.