This article supports the experience of those who explore what our
thresholds of percieving various sound effects are in the observation that
quick switching produces better results. Like the recent post which
explored the effect higher levels of perception provides verry strong
feedback upon the entering signal, this looks at lower levels where sound
discrimination first occurs.

http://www.eurekalert.org/pub_releas...-sna113005.php

" A team of Spanish and American neuroscientists has discovered neurons
in the mammalian brainstem that focus exclusively on new, novel
sounds, helping humans and other animals ignore ongoing, predictable
sounds.

These "novelty detector neurons" quickly stop firing if a sound or
sound pattern is repeated, but will briefly resume firing whenever
some aspect of the sound changes, according to Ellen Covey, one of the
authors of the study and a psychology professor at the University of
Washington. The neurons can detect changes in the pitch, loudness or
duration of a single sound and can even detect changes in the pattern
of a complex series of sounds, she said."
"