[LAD] LV2 mono instruments recommended?

Stefan Westerfeld stefan at space.twc.de
Sat Sep 10 14:21:03 UTC 2016


On Fri, Sep 09, 2016 at 09:55:59PM +0000, Rui Nuno Capela wrote:
> On 09/09/2016 06:33 PM, Stefan Westerfeld wrote:
> >
> > I have tested with Ardour and Qtractor. Ardour does what I'd expect: it plays
> > my instrument output on both channels. Qtractor however just plays my mono data
> > on one channel, the other is silent. Which is not what I want.
> >
> until the last release, qtractor used to replicate mono plugins as much 
> as audio output channels is for where it's inserted, so that you would 
> have exactly as many instances of a mono plugin as there are audio 
> output channels.
> unfortunately this "cleverness" didn't work well for all cases, 
> specially regarding instrument plugins vs. its own GUI state and 
> communication--quite often, only one plugin instance reflects some 
> changes done via the GUI, being one notable example about selection of 
> presets (only one instance would get it loaded one time). you would need 
> to save and reload the whole session to get everything in sync again.

Right. This particular "cleverness" would be wrong for the SpectMorph plugin as
well. Computing the audio data is quite CPU intensive, so if you would
instantiate it twice, you'd be wasting precious resources (for computing the
same data twice). Plugin UI problems would also occur.

> > So I am considering making my LV2 instrument always stereo, and just copy the
> > output buffer from left to right - this is cheap, and probably not much more
> > expensive than what the host would need to do anyway.
> >
> you don't really need to make it stereo all the way. at least on 
> qtractor, you can make use of balance.lv2 [1], inserted right after the 
> mono instrument and then set channel assignemnt = 1 (L->L, L->R) ...

Ok, I tried that, and this produces the intended result.

If you as host author say that this is the way Qtractor users should go for
mono instruments, I'll keep my plugin as it is, the other way would have been
kind-of a workaround. Still from the user experience I prefer what Ardour does,
as it automatically gets the intended result without the user needing to do

   Cu... Stefan
Stefan Westerfeld, http://space.twc.de/~stefan

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