Effect of carrier on the pitch of long duration vibrato tones

van Besouw, Rachel M. and Howard, David M. (2006) Effect of carrier on the pitch of long duration vibrato tones. Baroni, Mario, Addessi, Anna Rita, Caterina, Roberto and Costa, Marco (eds.) 9th International Conference on Music Perception and Cognition, Bologna, Italy. 21 - 25 Aug 2006. pp. 851-859 .

Abstract

Background  Previous studies on the pitch perceived for long-duration vibrato tones, where the modulator is a symmetric function (e.g. sine or triangular wave) have shown that the pitch perceived is generally the mean. For sinusoidal carriers modulated using a triangular wave is has been suggested that the pitch perceived is closer to the geometric mean than the arithmetic mean.
Aims  A pilot study was undertaken with the aim of exploring the effect of carrier on the perceived pitch and pitch strength of vibrato tones. The following carriers were investigated: a sinusoid, an impulse with four resolved harmonics of equal amplitude (including f₀), an impulse with twelve harmonics and an impulse containing the fundamental plus unresolved harmonics nine to twelve (all of equal amplitude).
Method  Pitch matches were obtained between modulated and unmodulated tones using a two-interval two-alternative adaptive procedure. The modulated tone was presented first, followed by one second of silence and then the unmodulated tone. Subjects indicated which of the tones was higher in pitch. Three carrier frequencies (f_c = ERBN no. 4 (123.2Hz), 10 (442.3Hz) and 16 (1051.1Hz)) were investigated for each of the four carriers resulting in twelve experimental conditions. In addition subjects were required to make unmodulated tone matches for all carriers at f_c = ERBN no. 10. Tone length was one second including 40ms raised cosine onset and offset ramps. The modulator in all cases was a sinusoid with an initial phase of 0 degrees, a rate of 6Hz and extent of .s 6% of f_c. All stimuli were presented at 45dBA.
Results   A two-way repeated measures ANOVA revealed a significant main effect of carrier, F(3, 39) =4.01, p < .05 and interaction between carrier and frequency. Overall there was much variation in the subjects’ responses and this variation tended to increase with f_c.
Conclusions  The results of this pilot study suggest that carrier type may affect the perceived pitch of tonesvibrato; however there was large variance in subject responses and so a long term study using fewer, highly trained subjects is currently being undertaken to corroborate these results.

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