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Richard Warren wrote:
>Since questions have been raised concerning vibrato, I would like to call
>attention to a remarkable observation reported by Seashore (University of
>Iowa Studies: Studies in the Psychology of Music, Vol. III, 1936, p. 105)
>that has intrigued me for some time, and wonder if anyone knows of an
>experimental verification of the phenomenon as described in the following
>... in the normal vibrato which involves pitch, loudness, and timbre,
>even the best ear can not isolate or identify these elements, to any
>satisfactory degree, by direct hearing. We make the situation even more
>critical and striking when we produce experimental tones in which we
>present either a pitch or an intensity pulsation alone and ask the
>musician to say which it is. Even under these circumstances, a good
>musician is quite unable to say which is which, even when the extent
>approaches the normal extent for pitch or intensity. For example, if we
>have in one case an intensity wave of 5 decibels and in another a pitch
>wave of a half-tone, he is almost as likely to call the intensity pitch,
>or the pitch intensity, as to call them correctly.... Many musicians will
>immediately take exception to this paragraph and say, "There is no danger
>in my confusing pitch and intensity in the vibrato." That is just
>another proof of the vitality of the illusion, because any one who has
>such a conviction quickly can be disillusioned by submitting himself to
>the test described.
Seashore's observation has been verified for very small, and rather rapid,
vibratos: It is impossible to discriminate a just-detectable sinusoidal FM
from a just-detectable sinusoidal AM if the modulation rate exceeds about 5
Hz. But the discrimination is possible is the modulation rate is about 2 Hz.
Demany, L., Semal, C. (1986). On the detection of amplitude modulation and
frequency modulation at low modulation frequencies. Acustica, 61, 243-255.
Moore, B.C.J., Sek, A. (1995). Effects of carrier frequency, modulation
rate, and modulation waveform on the detection of modulation and the
discrimination of modulation type (AM versus FM). JASA, 97, 2468-2478.