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

John Emmas johne53 at tiscali.co.uk
Thu May 20 04:18:31 PDT 2010

On 20 May 2010, at 11:23, John Rigg wrote:

> On Thu, May 20, 2010 at 12:49:22PM +1000, Ross Johnson wrote:
> The important thing is to avoid a discontinuity. This will occur
> if the sample value and the _slope_  (equivalent to dv/dt in analogue
> voltage terms) of the signal are not matched at the point of the
> join.
> It doesn't matter if the discontinuity in the spliced signal occurs
> at a zero crossing or anywhere else

Exactly - it's the slope that's important, not the sample value.  In fact, if both signals have identical amplitude and frequency content it could be argued that the safest place to produce a splice would be at the highest positive (or negative) sample value - since those are the places where the slope is gentlest and they're also the places where the reproduction device (i.e. the loudspeaker cone) will be stationary when the edit occurs.

Most people can visualize how difficult it would be to produce such an edit successfully - and yet they continue to believe that editing at a zero crossing is somehow easier (which it isn't, for all the reasons stated already).  So why does the "zero crossing" myth persist?  Simple....  it's because of the fact that in analogue terms, zero is the only voltage that's guaranteed to be present in all audio waveforms.  This leads people to believe (wrongly) that there's something intrinsically magical about it.

As others have stated previously cross-fading, whilst not bullet proof, is the best way to produce a click free edit in most cases.

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