discovered latency as LV2 in ardour

[mrmee]

i used Carla as LV2 plugin in Ardour in Linux. To describe the issue, here is what i did:

• routed track to a bus
• did a stem export of that bus
• loaded the stemfile as new track.
• checked for latency by switching phase of the stemtrack -> played both (stem and bus) -> no noise so they're perfectly in phase
• switched back phase to normal
• put a Carla-Plugin onto the stem and loaded a VST compressor

expected behavior: since Ardour has no bus latency compensation i tried this workaround to get some bus / parallelcompression of the bussignal. Big sound with the fatness of the compressorsignal + the transients of the bussignal.

experienced behavior: strong phasing. I did a cross-check with a Calf-Compressor put directly onto the track. -> no phasing, Bus and track are sample-perfect.

Suggestion: Carla has some internal latency that is not reported to the LV2 latency information variable correctly.

Question: Is this a bug or did i miss something in my workaround?

[falkTX]

maybe the plugin you loaded before introduces latency? carla as plugin does not report that value to the host yet.

[mrmee]

Reply after just two minutes. This is awesome!

If i understand plugin latency correctly this says the more plugins i load into Carla plugin the more latency i have to adjust by hand, right!?

Is there any method / workaround / hint to measure the caused latency?

[falkTX]

plugins (normally) do not add extra latency. the latency is a fixed value based on the current buffer size and sample rate. the few plugins that add latency do it because they need a specific amount of data before they can start processing.

at the moment carla does not expose latency information anywhere. I intend to add this information at least in the plugin settings.