[Ardour-Users] click free editing and zero crossings?

Paul Davis paul at linuxaudiosystems.com
Thu May 20 08:54:27 PDT 2010

On Thu, May 20, 2010 at 11:44 AM, John Emmas <johne53 at tiscali.co.uk> wrote:

> The only thing that's intrinsically helpful about zero crossings is that
> crossing point is guaranteed to exist in all alternating waveforms.

this discussion is continuing as if there is actually a sample of value zero
at a zero crossing, when there almost certainly is not. zero crossings
consist of two adjacent samples of opposite sign, and their existence says
absolutely nothing about the slope at the crossing, which in turn implies
that nothing can be taken for granted about the absolute values either.
without inserting a zero-valued sample into the data, there's nothing unique
about a zero crossing at all except the for alternation of sample value
signing. this generally implies that the point *between* the two samples is
at roughly at the DC offset of the signal (hopefully zero), but in a digital
signal this location is undefined since its an inter-sample location. the
actual cut has to be made on the earlier or later sample, neither of which
are zero.
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