Relationship between fundamental and formant frequencies in speech perception
Peter F. Assmann, Terrance M. Nearey · The Journal of the Acoustical Society of America · 2005
In natural speech, there is a moderate correlation between fundamental frequency (F0) and formant frequencies, associated with differences in larynx and vocal tract size across talkers. We have manipulated these properties using the Kawahara’s STRAIGHT vocoder to determine their contribution to sentence intelligibility, vowel identification accuracy, perceived gender, and naturalness judgments by human listeners. The results of these experiments, together with predictions from a pattern recognition model, suggest that frequency-shifted speech is more intelligible and perceived as more natural when the natural co-variation of F0 and formant frequency is preserved, even when frequency shifts exceed the range found in human speech.