[Audacity-devel] Zero crossing

[Ben C. <cro...@li...>]

Changing the amplification suddenly at a point where the waveform
 y(t) is nonzero causes
a discontinuity in y, and therefore a badly behaved fourier
series with lots and lots of spurious high frequencies.

Changing the amplification suddenly at a point where y=0 but
the derivative y'(t) is nonzero causes a discontinuity in y', which
has just as bad an effect on the fourier series.

In audible terms, I think /either/ result will probably be heard as
a click.

If you can find a point where y, y'', y''', etc. are
all zero up to infinitely high derivatives, then you can do whatever
you want there. In other words, you need an interval of pure
silence that lasts for a significant amount of time. I think this
is the only way to avoid a click.