vibrato

<http://sound.media.mit.edu/~brown/vibper2/vibper2/subsection3_5_1.htm
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Pitch center of musical sounds with vibrato.

"The determination of the pitch center of sounds that are frequency
modulated has been the focus of a number of previous studies. The
sources have usually been pure tones or synthetic complex sounds with
a well-defined spectral composition. In a musical context these
synthetic sounds differ in temporal and spectral properties from the
natural sounds produced by stringed instruments; and it is these
natural sounds which performers are trained to produce and to perceive
in order to make intonation choices. Samples consisting of
approximately 1 s of acoustic sounds produced by a virtuoso violist
playing the notes D4, C5#, A5, and G6 with and without vibrato have
been chosen for this study. The sounds without vibrato were then
resampled to give frequencies from -15 to +21 cents, with respect to
the geometric center of the sound, with vibrato. Experiments with
forced choice for pairs of sounds using musically experienced
listeners (including the violist who produced the original sounds) as
subjects will be reported. These experiments include a control set
consisting of the comparison of pitch levels of these same sounds
played without vibrato. Preliminary results with listeners who are not
string players are in accord with previous results, finding that the
pitch perceived is that of the geometric average."