Delay compensation bug when using automation with Vienna Ensemble Pro (VEP) plugin

[resonatee]

This affects 2022.7 and older. I already submitted this to Avid.

There is a bug that happens when starting playback where Pro Tools will not correctly asses the delay compensation buffer for Vienna Ensemble Pro (VEP) plugin when using automated parameters from VEP Server.
It makes sound distorted when automation parameters are received. It sometimes works properly without distortion, sometimes does not. When playback starts properly, the change of the buffers does not affect the quality of the sound and no distortion occurs.
I attached a video to showcase everything that happens:

https://drive.google.com/file/d/1WL2...f5I_D2KUz/view

Thank you for your time. Last version of Mojave cMP.

B

[Darryl Ramm]

Nice demo, that sounds awful :-(

Has dynamic delay comp like this ever worked?

I do wonder about how fast Pro Tools would have to respond to the change in latency to work, and whether this could ever be phase accurate. I know it's supposed to work, at least in other DAWs, but kinda amazes me it can.

[resonatee]

It seems to me, that what fails is 'negotiation' of the delay compensation value. Because at 0, it always stays right, also when it 'gets' it at the start of playback, you can play for long time (looping or not) and even while changing the value of delay, as i had shown in the video, the 'negotiations' are successful.

[resonatee]

Originally Posted by Darryl Ramm

Nice demo, that sounds awful :-(

Has dynamic delay comp like this ever worked?

The thing is, that it is not supposed to change during playback. The buffers are set and should stay there - they are set in multiplies of the playback buffer , so at 128 samples you get 1x128 2x128,4x128 or none.

[Darryl Ramm]

Originally Posted by resonatee

The thing is, that it is not supposed to change during playback. The buffers are set and should stay there - they are set in multiplies of the playback buffer , so at 128 samples you get 1x128 2x128,4x128 or none.

Gotcha. Should be easy for Avid to verify if the plugin is sending latency chance messages/callbacks and they should be ignored or something else is wrong. Did the folks at VSL say anything? It makes sense to me that Pro Tools needs to ignore latency change messages while the transport is running... it's just going to inject jumps in time which won't be good (maybe that's exactly the horrible noise you are hearing). But I wonder how this works, can plugins still send the latency change message (with some plugins not always going to be a buffer size change) and they are just ignored while the transport is running? Or are plugins inhibited from doing this while the transport is running?? Oh well, questions above my pay grade, but a curious corner or delay compensation.

[resonatee]

I hope it's a quick fix. I received replies from both Avid and Vsl, and Avid already started to investigate. We will see how that goes. In the meantime nobody replicated this?

case code is
"THP-2975 Bad distortion and Delay Compensation fluctuations when playing back automation in Vienna Ensemble Pro."