[LAD] stereospread.lv2 - Stereo spreading plugin (conjugate random phase all-pass filter pair)

[Florian Paul Schmidr]

Sorry for top-posting.

Fons, you are, of course, absolutely right. My thinking wasn't clear.

Applying them one after the other would cancel the effect, but summing does not.

Kind regards,
FPS

Nov 16, 2022 14:15:45 Fons Adriaensen <fons at linuxaudio.org>:

> On Wed, Nov 16, 2022 at 12:51:44PM +0100, Florian Paul Schmidt wrote:
> 
>> This ensures that what is a phase theta in the first filter becomes a
>> phase of -theta in the second filter, and summed that just gives a phase
>> of 0.
> 
> 1. If I understand this correctly the L and R outputs have opposite phase
>    shifts. That means they will not sum to the input. Just assume the L
>    shift is 90 degrees. then R is -90, and they will just cancel.
> 
> 2. If you measure this, you will also note amplitude differences between
>    L and R outputs. This is to be expected. Even if the two filters have
>    exact unity gain (and just a phase shift) at each frequency corresponding
>    to an FFT bin, the resulting filter will not be all-pass.
> 
> 3. At high frequencies (above 1 kHz or so), it's actually the amplitude
>    differences and not the phase shifts that create the stereo effect.
> 
> 
> Ciao,
> 
> -- 
> FA
> 
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