I ran into a really bad thing. I have many projects in which I use the guitarix plugins. I recently bought a new audio interface (Focusrite Scarlett 2i2 G4) and was very excited that I can run it with a buffer size as low as 256, which was not possible before, But today I found out that Guitarix (and ONLY Guitarix) does have massive problems with that. First I thought I have changed settings accidentally or so, I was even able to recreate the sound I wanted. But then I had another project with another guitarix plugin and that was totally broken. It was completely distorted and unusable. As I increased the buffer size to 1024 things went back to normal.
My question here is, how is this even possible? I always thought if the buffer size is too low there would be xruns (which weren’t at all), but not that a single plugin would fail. I know this is likely not an Ardour problem, but I wanted to know (and warn others) how this happens.
My guess is that the plugin in question uses its own background threads (perhaps for convolution), and doesn’t wait for the processing to complete.
Does it affect all gx* plugins? LV2? VST3? Which version of the plugins?
@brummer may be able to shed some light.
Thanks.
I did not test every possible plugin, affected were gx_cabinet, gx_amp and gx_alembic. Version is 0.47.0-1 from the Manjaro repo. I used LV2.
Those plugs use zita-convolver for convolution. As those they work best with a buffersize with power of two. That’s the case with a size of 256. Here they work as expected at 128 and 256. So I’ve currently no idea what happens.