Notes interrupted when recording starts in Ableton Live

[Scoox]

Ableton Liver version: v11.1.6
OS: Windows 11
Applies to: Seemingly all U-he plugins (tested with Diva, Repro-5 and Bazille

Steps to reproduce:

• Run Ableton Live and add an instance of Repro-5 to a MIDI track.
• Connect a MIDI keyboard and arm the Repro-5 track. Ensure you are able to play Repro-5 using the MIDI keyboard.
• In Repro-5, turn the Filter Sustain and Amplifier Sustain knobs to 100, to ensure the notes play indefinitely as long as MIDI keyboard keys are held down.
• Now press and hold one or more keys on your MIDI keyboard. The notes play indefinitely as long as you continue to hold down the keys.
• Click the record button in Live.

Expected: Notes continue to play after the last step, since you are still holding down the keys.
Observed: Repro-5 releases any keys that were playing before recording started, even though they have not been physically released.

I have not noticed this with other DAWs, and it doesn't seem to happen with other plugins.

[tasmaniandevil]

Ableton sends a reset on playback start, and the plugins listen to those reset commands.
This clears the audio buffer and ensures that things like reverb tails or delays that are still fading out will be reset and not ruin the start of the recording.

[Scoox]

Ableton sends a reset on playback start, and the plugins listen to those reset commands.

I didn't know that, but your explanation has been helpful. Interestingly though, not all plugins seem to listen for those reset commands. For example, Pigments in Ableton does not, but it does in FL Studio. I guess it's one of those standards that not everybody observes.

This clears the audio buffer and ensures that things like reverb tails or delays that are still fading out will be reset and not ruin the start of the recording.

OK, based on this it seems Ableton is at fault here. What I was trying to do is use count-in record. Ableton sends the reset command when recording actually begins (i.e. after the count-in), not when the user hits Record. The result is that the first note played by the user is interrupted the note starts just before count in expires, which is a normal thing to happen. Ableton still records it fine, but the plugin interrupts itself because it receives the reset command. I'll contact Ableton support about it.

[tasmaniandevil]

Some hosts will send that reset at the start of playback, others when playback stops, others might send it both times.
And it's something that every host seems to do slightly different.
Our plugins listen to this on playback start, but it also depends on the used host, the plugin format and the plugin, of course.

[gorbster]

I have been trying to troubleshoot this issue with Diva and Repro myself for a while and finally found another forum post describing the same problem. However this only seems to affect me with VST3 versions of the plugins (on my Apple Silicon machine, with Live 11.3 using latest versions of Diva and Repro). The VST and AUv2 versions don't exhibit the behavior. I'm following the same steps as OP outlines above.

Because the issue is not consistent across all plugin variants, it seems like it's unintended behavior. Is there a fundamental difference in the VST3 vs VST / AUv2 architectures?