[LV2] Lost due to no documentation on writing LV2 hosts

Robin Gareus robin at gareus.org
Sat May 26 18:55:11 PDT 2018

On 05/26/2018 09:50 PM, Juan Linietsky wrote:
> - I notice that a lot of plugins are stereo and mono. I remember from the
> LV1 days, that if you found a mono plugin, it was enough to just instance
> it twice.

For many plugins a replicated mono instances will produce a different
result compared to a dedicated stereo or multi-channel version.

e.g. when replicated, a compressor would compress each channel
separately. While a stereo compressor would use the same reduction for
both channels. The same is true for a Limiters and various other plugins.
Stereo reverbs can emulate a complete room, replicated mono reverb
instances cannot. Chorus/Phaser can use stereo-correlation etc.

> Here, not all mono plugins have a stereo version and many times there
> is no effective way to tell (if my host is stereo) how to ignore the
> mono version of the plugin in the listing.
It is up to the user, not the host, to decide which is the correct
approach. In some cases a user may want replicated mono instances for
artistic reasons.

> - When instantiating a plugin from the host, the host is supposed to 
> pass an array of LV2 features. Those are not defined anywhere, or 
> documented so I will happily assume that I'm not going to pass 
> anything and everything is going to work great, am I right?
Yes, except for plugins that depend on some specific feature.

http://lv2plug.in/ns/index.html lists them. The most commonly used
features are probably URID and Worker extensions followed by Instance


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