Thanks for this further suggestion! So you refer to sound_card_buffer_size here?
When I go below 512, I get no sound at all. With 512, the delay seems unchanged, but I get artifacts in the sound. With 1024 and above, sound is ok, but the delay if still there. Not being able to go lower is probably a limitation of my sound card…
Also, I am wondering why the tb303 does not show any visible delay, as it should also be affected by the buffer boundary “error”.
In the project where the issue first appeared for me, I could circumvent its audible effect by shortenting the first note played by the respective synth (published to in_thread here). But still, I would be interested in ways to preventing the issue from ground.