We have encountered a strange problem with AAX plugin in Pro Tools.
The playback (without recording or input monitoring) is crackling if the project bit depth is 16 bits but not when it is 24 bits. The sample rate does not affect this only the bit depth. No problems when recording, only when playing back.
Has anyone experienced similar problems?
Did you try reproduce this with Juce Demo Plugin?
Is this Mac/PC? What Pro Tools version?
would be helpful 
I recently noticed a warning about low buffer sizes on macOS on the Pro tools system requirements page: http://avid.force.com/pkb/articles/compatibility/Pro-Tools-System-Requirements
No mention of bit depth-related issues though…
Just tested my Juce-based AAX plugin in Pro Tools Ultimate 2018.7.0 on Windows 10 (latest updates), and I could switch my Session setup between 16-bit and 24-bit without any problems.
We found out that it was a Pro Tools problem after all. Crackling happens also with other plugins with many systems. Selecting 24 bit output fixes it.
Jussi
