[Ardour-Users] Slice marks makes noise

Paul Davis paul at linuxaudiosystems.com
Sun Oct 28 10:04:23 PDT 2018

On Sat, Oct 27, 2018 at 9:55 PM Al Thompson <althompson58 at gmail.com> wrote:

> But they do in a sine wave, which is the example given.

They don't exist in the overwhelming majority of sine waves.

A true "zero crossing edit" requires that there is a sample of value zero
where the edit/cut can be applied.

Almost all sine waves will instead have a pair of adjacent samples slightly
and slightly below zero. How "slightly" depends on the sine wave frequency
and the sample rate.

If you cut at one of the adjacent samples, you are actually creating a
discontinuity in the output, the audible impact of which will depend on a
variety of factors. Obviously, the if chosen sample's value is very close
to zero, then the effect will be fairly similar to the "true zero crossing"

Apply this to real world audio, with much more complex signals than a
single frequency sine wave... the results of the "zero crossing edit" not
actually using a zero value are much more likely to be an audible
discontinuity (aka "pop" or "click").

This is why Ardour doesn't bother with attempting to "find a zero
crossing", and instead applies a predictable and controllable fade on each
side of the cut. Even this cannot be guaranteed to work - there is always a
hypothetical pathological case where it fails - but it is much more
reliable than the "zero crossing' woo that somehow made into digital
editing lore some years back.
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