pers
NatureRecordists:
Hope I'm not the only one who is finding this thread to be quite productive=
;
if so, please advise and I'll not pursue it further on this forum.
Walter Knapp's latest reply finally sparked what I think is a highly likely
hypothesis. Whereas, with a single sound source something like multi-
pathing can create the reported effects (e.g., ghosts on a TV image), if
there are multiple sources at similar frequencies then the effects of
constructive/destructive summation are inevitable (e.g., beats between
engines on any multi-engine aircraft). No non-linearity is required. This
is a simple consequence of convergence of multiple acoustic waves,
and affects the instantaneous sound pressure level at the microphone
just as at our ears. And the effect is not amplitude dependent in the
sense that overload distortions are.
This multi-source interference is not often encountered in any birds that
I have typically recorded, but it is certainly a fact of acoustic life in
many
other situations such as vocalizing choruses of insects and amphibs.
Mea culpa; I should have thought of this hypothesis much sooner.
Good recording,
Randy
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