Logic Pro X - delay compensation limitations?

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Level 1

8 points

Logic Pro X - delay compensation limitations?

Hi all! I am trying to move from Pro Tools HD to Logic for some mixing (big leap, I know - long story there), and am finding the delay compensation documentation to be pretty lax, and the actual compensation's effectiveness to be foggy at best. Despite having Delay Compensation set to All, and toggling that setting off/on a number of times with no difference, I am experiencing audible delays in my mix with plugins that are heavy in latency. I am worried that plugins with low latency are also introducing phase and cancellation/summing issues in the mix that I'm fighting without knowing it.

My question is, is there community confidence that delay compensation is working properly within Logic Pro X as described (calculates total delay from plug-ins and offsets each channel, per Delay Compensation setting, so that all tracks play back in sync)? If so, is there a limitation to how much delay it will offset? For example, I have one plug-in that is currently introducing 33ms of delay, and putting that as an insert on a track instantly whacks that track out of place with the rest of the mix. Same deal on a bus, and only on the master can I insert it without negative impact as it's delaying the entire stereo mix uniformly.

Tests I've run (and feel free to challenge my methodology or suggest alternate ways to proof this, I'm very open to learning opportunities here) -

Delay-inducing plugins on channel insert, bus insert, master insert - bounced each variation to confirm the audible delay was passed to the output file (it was)
New project, imported identical audio file to two tracks, phase inverted one track, confirmed silent playback (full cancellation). Added a delay-inducing plugin to one track and confirmed I was able to hear part of the waveform on playback (indicating delay disrupting the 100% phase cancellation).
Same test as #2 except using a very low delay inducing plugin (1.6ms - Soundtoys Decapitator with the mix set to 100% dry) and heard silence. Exporting the file to iZotope RX showed some spectral data but I can't tell if that's a plugin delay issue so I'm not correlating it at this point.
Same test as #2 except using a very long delay-inducing plugin (there's a build of AFX2DAW that induces 330ms of delay). Observed that the track initially was about 1/3 second delayed upon applying the plugin, but Logic did recalculate and then only some of the file was audible indicating improved but not 100% compensation.

System:

MacBook Pro M1 16GB on 11.6 Big Sur (holding on updating to Monterey)

Logic Pro 10.6.3 (holding on updating to 10.7)

Antelope Zen Go (the source of a lot of this frustration as the AFX2DAW bridge plugin adds a minimum 33ms delay, but the plugins sound pretty darn good)

Thanks in advance!

MacBook Pro 13″, macOS 11.6

Posted on Nov 3, 2021 3:12 PM

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Answer 1

Nov 4, 2021 7:59 AM in response to tannercundy

Hi,

Welcome to the world of Logic... The subject of Plugin Delay Compensation ("PDC") is a bit of a beast and I'll try to offer you some insights and observations.

Personally I find as a session builds and the mix gets more complex I find that there is a noticeable delay between hitting play and hearing sound. I use loads of Universal Audio plug-ins with external processing and the end results *seem* to be fine and no issues with bounces.

In general I find that PDC in Logic works pretty well BUT there are some routing situations that can cause PDC problems. There is a thread on the site LogicProHelp that has been running for 3 years on bugs and issues with PDC and every time one issue is fixed it seems another issue appears. ( search for "Plug-in Delay Compensation broken with external side-chain").

I tried your test ( a , inverted a ) and here is what I observed. Any plug-in that added any "colour" in the emulation were not 100% cancelled (silent). Example add a compressor on one of the two tracks. But add the identical compressor on both tracks BUT prior to the phase inversion and the result was full cancellation. Also tried with a UAD Massive Passive and same results with PDC working. Also tested Decapitator and dry 100% was in phase. I was not able to induce any delays in the ms range.

So I think the issue could be either the third party plugins you are using adding color OR issues that relate to routing and PDC. Are you using any side-chain inputs from another bus? There is still a PDC issue if you use a bus as a side-chain (input) to a plug-in on another bus ( e.g. vox bus to duck a drum bus with a compressor ). This is the topic of the thread on LogicProHelp.

Here are my observations and suggestions based on 10.6.3 on Catalina:

Make sure any third party plugins and drivers are up to date. CRITICAL
Preferences : Audio : General : Plug-In Latency set to "All". This is critical if any processing is external to LPX.
Preferences : Audio : General : Plug-In Latency "Playback Pre Roll "On".
I run with a buffer at 1024 for mixing
In some cased the UI on third party plugins (like a meter) will be AHEAD of the sound. It seems that the PDC is not being managed properly in some plugins UI but not the sound.

I hope some of this helps with your perspective.

Don

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Answer 2

tannercundy Author

Level 1

8 points

Nov 4, 2021 1:37 PM in response to Don Mactavish

Hi Don, I appreciate the reply!

I've done a full sweep of the plug-ins in use and verified they're all up-to-date. Similarly, I am running 'All' on Latency and have tried cycling that to Off and back to All in case there's a settings cache issue. Historically I've found pref files in the Pro Tools HD realm that needed trashing on occasion, but couldn't find much documentation for Logic on anything of value there.

I frequency cycle buffer settings (have been running at 32 or 64 for tracking, 256 for mixing) and will bump that up to 1024 tonight to see if that helps. Perhaps the PDC bumps up against a governor when the buffer is set relatively low.

What I am experiencing is definitely in audio, and not in the UI, and separate from any playback start delay - it's in the mix itself, which is why I'm immediately concerned. If I, for example, am using additive EQ to restore low-frequency content in kick drum tracks that are experiencing phase cancellation due to PDC not working as I would expect, that's a problem.

I follow your call-outs about coloration plugins and have been testing at 100% dry, as I am not aware of any other ways to invoke the plug-in delay and have it pass clean, but delayed, signal. Any trickery there (does having the plug on the insert chain induce the delay even if the plug is off, for example?) would help and I'm happy to re-test.

Two contributors, as I'm thinking through this - I'm coming from a DAW that reported, in samples, the delay on each channel being applied, which gave me a metric to quickly validate if compensation was accurate to the insert stack and project delays due to bussing. Since I don't have this here, I've lost a validation path and am having to trust a new DAW. Scary stuff! :)

Additionally, I'm on an M1 platform with some plugs still using Rosetta, and trying to bring in the DSP-enhanced plugs from my Antelope - which is having its own set of significant challenges in getting their bridge plugin to work properly. It's possible that the delay from that plugin isn't reporting accurately or is bugged to the point of throwing Logic's PDC scheme into disarray.

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Answer 3

Nov 5, 2021 5:39 AM in response to tannercundy

Hi Tanner,

I am still on Catalina and thus no experience with Rosetta ( too many projects on the go to risk a migration at this point). Your thinking, testing and knowledge are solid on the issues and you may be hitting a bug or compatibility issue. You may want to post your issue over on LogicProHelp, some others may have some suggestions on dealing with Rosetta and PDC. The move to Big Sur followed by M1 has been a challenge for many (really good) third party vendors. Hopefully Antelope will have updates soon.

Do the community a favour and keep us posted on your issue and discoveries.

Best regards

Don

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Logic Pro X - delay compensation limitations?

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