[LAD] LV2 mono instruments recommended?

Rui Nuno Capela rncbc at rncbc.org
Fri Sep 9 21:55:59 UTC 2016

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.

> 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) ...

[1] http://gareus.org/oss/lv2/balance

rncbc aka. Rui Nuno Capela

More information about the Linux-audio-dev mailing list