Page 95 - The Master Handbook Of Acoustics

70 CHAPTER THREE

At one time this 200 Hz was called “periodicity pitch” but so-called
“pattern” theories dominate today. The auditory system is supposed to
recognize that the upper tones are harmonics of the 200 Hz and sup-
plies the missing fundamental that would have generated them. This is
a very interesting effect but explanations of it are highly controversial.

The Ear as an Analyzer

Listening to a good symphony orchestra in your favorite concert hall,
concentrate first on the violins. Now focus your attention on the clar-
inets, then the percussion section. Next listen to a male quartet and
single out the first tenor, the baritone, the bass. This is a very remark-
able power of the human ear/brain combination. In the ear canal, all
these sounds are mixed together; how does the ear succeed in separat-
ing them? The sea surface might be disturbed by many wave systems,
one due to local wind, one from a distant storm, and several wakes
from passing vessels. The eye cannot separate these, but this is essen-
tially what the ear is constantly doing with complex sound waves. By
rigorous training, a keen observer can listen to the sound of a violin
and pick out the various overtones apart from the fundamental!

The Ear as a Measuring Instrument

The emphasis on the distinction between physical measurements and
subjective sensation would seem to rule out the possibility of using the
ear for physical measurements. True, we cannot obtain digital read-
outs by looking in someone’s eyes (or ears), but the ears are very keen
at making comparisons. People are able to detect sound-level differ-
ences of about 1 dB throughout most of the audible band if the level is
reasonable. Under ideal conditions, a change of a third this amount is
perceptible. At ordinary levels, and for frequencies less than 1,000 Hz,
the ear can tell the difference between tones separated by as little as
0.3%. This would be 0.3 Hz at 100 Hz and 3 Hz at 1,000 Hz.
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The eminent Harvey Fletcher has pointed out how the remarkable
keenness of the human ear saved the day in many of his researches in
synthesizing musical sounds. For example, in his study of piano sounds,
he initially postulated that all that is necessary is to measure the fre-
quency and magnitude of fundamental and harmonics and then combine