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

Jörn Nettingsmeier nettings at stackingdwarves.net
Wed May 19 03:15:07 PDT 2010

where does this myth come from that edits at zero crossings are
something particularly desirable? editing at a zero crossing *does*
*not* mean you get a click-free junction.

we're in a discrete world, so yes, the wave form is discontinous at
every sample. that's not an issue. the important question is: are there
so many new overtones generated by an edit (and not masked by content)
that it begins to sound bad? or, to put it another way: does the
waveform change direction in an extreme way?

to see why zero-crossing edits don't always work, imagine some region
containing a simple low-frequency sine wave. say it approaches its end
point (which is at a zero crossing) from the positive half-cycle. now
splice another similar sine wave to the end of the first region. say it
begins at a zero crossing, but it moves upward, into the positive
half-cycle, immediately. presto: a nice zero-crossing edit with a
horrible click.

       *       |       *
   *       *   |   *       *
 *           * | *           *

the only way around this is a crossfade (which basically means a
low-pass filter at the edit point).

/me leaves soapbox now.

Jörn Nettingsmeier
Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487

Meister für Veranstaltungstechnik (Bühne/Studio), Elektrofachkraft
Audio and event engineer - Ambisonic surround recordings


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