The Effects of Masked and Delayed Auditory Feedback on Fundamental Frequency Modulation in Vocal Vibrato

Although relatively precise control over the extent and rate of fundamental frequency (f_o) modulation may be needed for optimal production of vibrato, the role of auditory feedback in controlling vibrato is not well understood. Previous studies altered the gain and timing of auditory feedback in singers producing vibrato and showed inconsistent effects on the extent and rate of f_o modulation, which may have been related to small sample sizes or limited analyses. Therefore, the purpose of this study was to further investigate whether the gain or timing of auditory feedback impacts control of vibrato in a larger sample of speakers and with advanced statistical analyses.

Ten classically-trained singers produced sustained vowels with vibrato while their auditory feedback was masked with pink noise or multi-talker babble to reduce the gain of their auditory feedback and while their auditory feedback was delayed by about 200 or 300 milliseconds to alter the timing of their auditory feedback. Acoustical analyses measured changes in the extent and rate of f_o modulation in the masked and delayed trials relative to control trials. Bayesian modeling was used to analyze the effects of noise-masked, babble-masked, and delayed auditory feedback on the extent and rate of f_o modulation.

There was compelling evidence that noise masking increased the extent of f_o modulation, and babble masking increased the variability in the rate of f_o modulation (ie, jitter of f_o modulation). Masked auditory feedback did not affect the average rate of f_o modulation. Delayed auditory feedback did not affect the extent, rate, or jitter of f_o modulation.

The current study demonstrated that reducing the gain of the auditory feedback with noise masking increased the extent of f_o modulation but did not affect the average rate of f_o modulation in classically-trained singers producing vibrato. Reducing the gain of the auditory feedback with babble masking and altering the timing of auditory feedback with imposed delays did not affect the average extent or rate of f_o modulation. However, babble masking increased the jitter of f_o modulation rate, which suggests that modulated auditory feedback may affect the periodicity of f_o modulation from one modulation cycle to the next. These findings clarify the role of auditory feedback in controlling vibrato and may inform the current reflex-resonance models of vibrato.