Vocal matching of frequency modulation in synthesized vowels

Nine male singers attempted to match rates and extents of synthesized vocal vibrato at low, middle, and high pitch levels. The results showed that on average, the singers were able to match rates of 3, 5, and 7 Hz within 13%. It was difficult for the singers, however, to match extents of 0.5, 1.0, and 1.5 semitones. Thus, the results indicated singers' reasonably good ability to match rates but, contrary to prevalent opinions, not extents of vocal vibrato.