[PD] Equal-power crossfade?

[Scott Nordlund]

> Le 2012-02-06 à 13:13:00, Scott Nordlund a écrit :
>
> > Incidentally I'm working on a frequency domain algorithm that forces
> > mixed signals to be correlated and in phase, by summing their
> > magnitudes. But it's no magic trick since it does this by inducing a
> > time varying phase shift. This isn't the silver bullet that you might be
> > hoping for, but I think it should make a neat variation of the usual
> > chorus effect.
>
> This means you do FFT, then convert to polar, then do linear crossfade in
> the shortest of the two paths ? (so that the phase shift is always between
> -π and +π)
>
> If you do it quickly, it becomes a pitch shift, but if not panning too
> fast, it shouldn't be a problem. 

It's not specifically intended for a crossfader (though it could easily be used that way), just summing in general. It's a typical weighted-overlap-add FFT thing. The magnitude of the output is the sum of the input magnitudes (so they're effectively always in phase and never cancel). The phase can be a number of things: the phase of the sum of the inputs (i.e. the phase of the usual vector sum), or the phase of the input with the largest magnitude (per bin), or either of those but constrained to be within a certain range with respect to one of the inputs... or something like that. I haven't had a lot of time to mess with it, but it's been in the back of my mind as a generally neat idea.