Bitwig sends polyphonic modulation values before but not after note on events

[robbert-vdh]

Right now Bitwig always sends polyphonic modulation every 64 samples with no regard for note start times. This results in notes/voices potentially getting their first polyphonic modulation value up to 63 samples after the note start. Before that point the note ID doesn't technically exist yet, and Bitwig is sending invalid events for invalid note IDs. This looks a little something like this:

To fix this, Bitwig would need to (re)send the initial modulation value just after the CLAP_EVENT_NOTE_ON event.

[swesterfeld]

I think what I'd like to have from a plugin point of view to get the initial value for the modulation right would be this:

1. the host should never send a modulation event for a clap_id before the note on event for this clap_id
2. for parameters which are modulated by clap_id, the host should send the initial value for the modulation with the same time stamp after the note on event for this clap_id
3. for parameters which are modulated by channel/key, the host should send the initial value for the modulation with the same time stamp after the note on event for this channel/key
4. for parameters which are modulated for all voices, the plugin should track the state of the global modulation and copy it into new voices

See also https://github.com/free-audio/clap/discussions/316

@abique what do you think?

• Is my unterstanding of what I can expect from Bitwig correct here?
• From my tests, Bitwig doesn't follow points 1 and 2 here (I don't know how to test 3), can I do anything else to help this getting fixed (like contacting tech support)?
• Should this be documented in the CLAP spec so that plugin writers can rely on this behaviour?

[abique]

Should be fixed for Bitwig 5.0 Beta 7.

[robbert-vdh]

Very excited to give that a try, should make a huge difference when using polyphonic modulation with extremer values!

[abique]

@robbert-vdh did you have a chance to test this? BTW, I've changed a bit that code for the beta 9.

[robbert-vdh]

I tried testing this with Beta 9 but I'm running into audio engine crashes and I was getting out of bounds events at one point. I submitted a crash report. And here's the backtrace with no symbols if you have a way to retrieve those from the offsets:

``` 0. /opt/bitwig-studio/bin/BitwigAudioEngine-X64-AVX2(+0x384f097) [0x55f5d772d097] 1. /opt/bitwig-studio/bin/BitwigAudioEngine-X64-AVX2(+0x38522fb) [0x55f5d77302fb] 2. /usr/lib/libc.so.6(+0x39ab0) [0x7f16db278ab0] 3. /opt/bitwig-studio/bin/BitwigAudioEngine-X64-AVX2(+0x3634d6e) [0x55f5d7512d6e] 4. engine::AudioBuffer::madd(engine::AudioBuffer const&, float, unsigned int) 5. /opt/bitwig-studio/bin/BitwigAudioEngine-X64-AVX2(+0x33b82bb) [0x55f5d72962bb] 6. /opt/bitwig-studio/bin/BitwigAudioEngine-X64-AVX2(+0x2f635ba) [0x55f5d6e415ba] 7. /opt/bitwig-studio/bin/BitwigAudioEngine-X64-AVX2(+0x2f3d0a4) [0x55f5d6e1b0a4] 8. /opt/bitwig-studio/bin/BitwigAudioEngine-X64-AVX2(+0x2f497ab) [0x55f5d6e277ab] 9. /opt/bitwig-studio/bin/BitwigAudioEngine-X64-AVX2(+0x2f464c9) [0x55f5d6e244c9] 10. /opt/bitwig-studio/bin/BitwigAudioEngine-X64-AVX2(+0x2ff96dd) [0x55f5d6ed76dd] 11. /opt/bitwig-studio/bin/BitwigAudioEngine-X64-AVX2(+0x2f201c2) [0x55f5d6dfe1c2] 12. /opt/bitwig-studio/bin/BitwigAudioEngine-X64-AVX2(+0x387c698) [0x55f5d775a698] 13. base::core::Thread::thread_run_func(void*) 14. /usr/lib/libc.so.6(+0x8744b) [0x7f16db2c644b] 15. /usr/lib/libc.so.6(+0x10ae40) [0x7f16db349e40] ```

[abique]

@robbert-vdh I think it isn't crashing anymore. I'll double check that shortly.

[abique]

@robbert-vdh please re-open if not fixed for you. I've just verified it and looks good to me.