Delay compensation bug after Pro Tools update.

[XJENSEN]

Exactly. I reported this bug to AVID about 3 years ago.

[Darryl Ramm]

Originally Posted by XJENSEN

Exactly. I reported this bug to AVID about 3 years ago.

Hi

Who are you replying "Exactly" to? If me/you were seeing disk I/O buffer size related issues... Do you have a bug number? Case number? What description you sent to Avid support? Did disabling LLM or disable "Allow Sends to persist during LLM" change the behavior? Would be great either way to confirm this is or is not related to the other LLM/sends issue(s).

[quadraphonics]

Thank you Darryl.

I am running an HDX system, so I don't have the option to turn on LLM. You are correct in that I am running 48k sessions and the H/W buffer is set to 1024 samples. I will keep playing with this and report back.

Randall

Originally Posted by Darryl Ramm

There seems a few ways Pro Tools can mess up with large delay compensation errors: where an incorrect delay compensation equal to the disk playback buffer (not H/W buffer) is applied (so 1024 or 2048 samples depending on sample rate). These issues might all trace back to the same root cause. If you pull off other plugins in that track's delay comp chain I suspect you may see exactly 1024 samples latency (and I assume you are at 44.1 kHz or 48 kHz? so a 1024 sample disk I/O buffer). It may be worth making a copy of your session that you can hack up to do that and more to play here.

These problems may have been introduced when Avid added "Allow Sends to persist during LLM" but IIRC that was in 2018.7 so the same bug might have been in 2020.12, but maybe you had different preference settings and were not seeing the bug. I have also not gone looking back at behaviors in past Pro Tools releases. The problem other folks have seen are manifest in one case where you have a H/W insert following a plugin, have "Allow Sends to persist during LLM" enabled and have LLM on. Disabling LLM or "Allow Sends to persist during LLM" in that case avoids the problem. This is Pro Tools bug PT-293686 been reported to Avid for months now, with trivial way to reproduce. There are other ways a similar delay comp error can occur.

I'm a complete idiot when it comes to hybrid engine, have never used it, etc. (please send me some HDX cards and a MTRX and I'll explore this bug for ya all ). But for the heck of it you could try disabling "Allow Sends to persist during LLM" and LLM if they are even options (makes sense they could/should be but I am not sure) and see if this changes the behavior.

Of course there may be other issues, plugins with broken delay comp, yet some other Pro Tools delay comp issue, some weird issue with routing, etc. but it would be great just to see if what you are seeing might be related to these other known problems.

[Darryl Ramm]

Originally Posted by quadraphonics

Thank you Darryl.

I am running an HDX system, so I don't have the option to turn on LLM. You are correct in that I am running 48k sessions and the H/W buffer is set to 1024 samples. I will keep playing with this and report back.

Randall

Hi Randall

To be clear the bug I am talking about causes incorrect delay compensation offsets based on the disk IO buffer not the HW buffer size. Pro Tools has two different buffers, aka split buffers. The disk IO buffer is the high latency buffer used for playback only and you cannot directly control its size. At 44.1kHz [edit:] and 48kHz it is 1024 samples. If you change the HW buffer size to a small value and the delay you are seeing does not change then it’s possible your problem is related to these other ones I mentioned. If it reduces with the HW buffer size it is likely not related. I don’t want to waste your time, but that quick test might still be interesting.

I know HDX does not have LLM, it was what happens when the hybrid engine I was not clear on. It seemed at least in principle could support LLM.