[PD] a smooth crossfade for "equal" signals (freezing/unfreezing)
Mathieu Bouchard
matju at artengine.ca
Mon Jul 18 19:39:48 CEST 2011
On Fri, 8 Jul 2011, Alexandre Torres Porres wrote:
> It seems now it's a matter of aligning the phases, but not sure how, good night
Phase alignment has to be done by a slight temporary pitch shift. You can
shift up or shift down, but in any case, you need to shift.
If you do a plain linear cross-fade of signals (or a plain linear
cross-fade of spectra, which is the same thing), it will automatically do
this temporary pitch-shift, but will also do a temporary amplitude-drop at
the same time.
This is because if you have two dots on a circle representing two phase
alignments at the same amplitude, and you go from one to the other, you
will go inside of the circle, where the amplitude is lower. The centre of
the circle represents silence. In the extreme case of complete reversal of
phase, the crossfade will quickly go through the silence point. But each
frequency will have a different crossfade, so, overall, the amplitude drop
will rarely be great, except if you tend to have few partials.
I'm thinking about phasor diagrams like
http://en.wikipedia.org/wiki/Phasor , which may be considered as a use of
Argand diagrams (complex numbers plane).
To keep constant amplitude, if you want to, is like rotating dots so that
they keep the same amplitude (distance from centre). This is usually not
easy to do, but you already have a components representation using
sigmund~, so you have the opportunity to fudge the freqs a bit...
_______________________________________________________________________
| Mathieu Bouchard ---- tél: +1.514.383.3801 ---- Villeray, Montréal, QC
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