Re: [LAD] [EPAMP] an effect plugin API for media players: anyone interested?

On Mon, Jun 02, 2008 at 03:58:48PM +0200, Stefano D'Angelo wrote:

> With 'converting stereo to 5.1' I was meaning something like this (roughly):
> left_out = surround_left_out = left_in
> right_out = surround_right_out = right_in
> lfe_out = center_out = (left_in + right_in) / 2
>
> (or lfe_out with some kind of low-pass filtering, you choose)

There are many ways to get a usable 5.1 signal from stereo,
but this is not one of them. It's wrong on all accounts.
If you build this into a host you can't even have a plugin
that does it right. Unless you tell it to ignore everything
but the L and R inputs which happen to be the the original
stereo signal. In that case you could as well just give it
those two signals, and not bother about the conversion.

What is needed to do stereo to 5.1, or even to just play back
5.1 correctly depends on the actual (hardware) 5.1 system that
you are driving. A system consisting of 5 small cubes and a
sub needs different processing than one having 5 full range
speakers. The required processing may be done in the amp, or
not, in which case a plugin has to do it. And that's just 5.1.
There's also stereo, 7.1, binaural, ambisonic, etc.
A decent media player should be able to render any input
format to whatever speaker setup the user has, and make
the best of it. This is a very large number of conversions
each of them can have many variations. Which is why you
need plugins.

> This is true. But this is true for LADSPA (LV2 too?) as well.
> Ok, I'm thinking about it for the next draft.

LV2 would at least allow to have informative port names and
types, and provide information to a host what they represent
and how to use them.

Ciao,

-- 
FA
Laboratorio di Acustica ed Elettroacustica
Parma, Italia
Lascia la spina, cogli la rosa.
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