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Minor third

Dear List,

In a very speculative way one could assume that one reason for
minor-third calling is to avoid possible masking by unexpected
environmental sounds. Assuming that many environmental sounds have a
spectrum varying strongly as a function of frequency (that is with the
amplitude in one frequency band not correlated strongly to the amplitude
in other frequency bands) it would be advisable to code your message
such that it involves two different frequency bands so that if one of
these two bands is masked only half of the message is lost. That would
be better than a 50% chance that the entire message is lost because
speech is redundant, and because the recipient might solicit a resend of
the message.

Al argues that small intervals are favorable for coherence, so the task
is to find the smallest interval that grants the involvement of two
different frequency bands. The width of frequency bands in human hearing
is a third of an octave, i.e. a major third. From this reasoning it
would follow that third-calling would better make use of major thirds
than of minor thirds. But then: how could our ancestors know the width
of frequency bands with semitone precision long before Fletcher :-?

Christian Kaernbach

Al Bregman replied to Jeremy Day-O'Connell:

Regarding the second point, I would imagine that the opposite would be
true:  the larger the interval, the more difficult it would be to track
the sequence in a noisy real-world situation.  Small intervals favor
coherence; in an A-B sequence, the larger the interval between A and B
(i.e., the smaller the similarity between them), the greater  the
likelihood that one of the sounds (A or B) will find a more similar
sound to group with than the other sound of the A-B sequence.

This means that BOTH the vocal ease and the perceptual coherence would
favor small intervals.