Dealing with external ADAT converter latency

[Phil O'Keefe]

I'm using an external ADAT converter to increase the input count on my Carbon setup, and running external mic preamps into that.

The ADAT converter I am currently using has 1.46 ms of delay at 44.1 kHz. What is "best practice" for dealing with this converter latency? Just nudge the tracks earlier by 1.46 ms after a recording pass? Any advice and suggestions are welcomed. Thanks!

I'm running Pro Tools Ultimate 2021.12, PT Carbon, Mac mini M1, 16GB, MacOS 12.1 (Monterey)

[Darryl Ramm]

Sadly your best route is Nudge-o-Matic wetware... folks have asked for configurable delay options in the past... nothing happened AFAIK.

[JFreak]

Doesn't carbon have that automatic latency compensation on IO setup?

[BScout]

Originally Posted by JFreak

Doesn't carbon have that automatic latency compensation on IO setup?

It only compensates for its own hardware.
It doesn't compensate for devices attached (which add additional latency.)

To the OP, you can use user offsets (per track) for latency but it gets messy. It's easier to set a nudge value and then nudge post-record.

For inserts, you can compensate the round trip in I/O. There's been a long standing request to make that sample based (so changing sample rates, you don't have to correct) but that's not been implemented yet.

[martthie_08]

thanks for raising awareness on this issue,
to be honest I never thought of that up until now.

I think the most elegant way to deal with this would be to use a plugin that can provide a negative timing offset on the ADAT input tracks, like Precision Time Align from Eventide for example.

It would be of course much better if ProTools allowed you to enter a user offset for recorded tracks on ADAT inputs - although I image that would get really messy with things like Destructive / Punch record.

And to the previous poster: YES, PLEASE AVID add sample based I/O offsets and PLEASE rework and update the I/O Plugin while you are at it - it could really use a visual indication for clip overs and input/output levels.

[Darryl Ramm]

Originally Posted by martthie_08

I think the most elegant way to deal with this would be to use a plugin that can provide a negative timing offset on the ADAT input tracks, like Precision Time Align from Eventide for example.

I would think Precision Time Align would be awful here. Presumably folks got Carbon because they care about low latency and tracking though HDX plugs, Precision Time Align adds something around 500 samples of latency (at least at 48 kHz) and then does negative values by reporting different delay comp values to Pro Tools and lets Pro Tools time align stuff using it's standard delay comp. It's the last thing you want on a live input.

Or are you thinking workflows where the Precision Time Align plugin is made inactive during tracking and then activated during mixing? That still seems cumbersome to me, but so is nudging by hand.

I'm waiting for a Tardis plugin to do this properly, and that might well happen before Avid ever gets to supporting configurable conversion time in Pro Tools. :-O

[albee1952]

I'm curious, are you thinking there is an issue when there really isn't? Every converter has latency and all will be very close, given the same buffer setting. Any difference is likely to be not more than a few dozen samples(read inches in the real world). So, I can see how this would matter if you put one overhead mic thru the Carbon preamp and another overhead thru an external(something I would never do, but for completely different reasons than possible converter latency). What exactly are you doing where it presents an audible problem?

[martthie_08]

Originally Posted by Darryl Ramm

Or are you thinking workflows where the Precision Time Align plugin is made inactive during tracking and then activated during mixing?

yes, add it when mixing...
Nudging or moving tracks around seems awfully error-prone, especially when working with many takes / playlists.

The thing to remember is that even AAX-DSP Plugins add latency. When recording multi-mic'd sources (think drums), you want to have the same plugin on each individual track, even if bypassed, just to make sure the latency is exactly the same.
Otherwise you would get a different result when monitoring the input as opposed to playing back the recording (when plugin delays are compensated).

what I am getting at here is that even the Carbon conversion has an inherent (unknown?) latency that gets automatically compensated after you hit stop on the recording.
so without knowing that latency, there would be no point in even trying to match the differences of your ADAT connected converter box (I am using an Audient ASP800) while tracking with AAX-DSP delay plugins.
For this reason, I try to keep multi-miced sources on the same converter, either the internal Carbon or external ADAT connected.

[JFreak]

Exactly.

Modern boxes have conversion latency of way below 10 samples and should there be a problem between different kind of boxes it would be different amount of converter latency. And again, as said, no matter how you calculate it that would be less than 10 samples any day, unless you manage to find a very old and slow box.

10 samples would be 10samples/48samples-per-millisecond=0.2ms Now let's assume speed of sound in air is same everywhere, it would be 343 meters per second, or 343 millimeters per millisecond. Which means 0.2ms*343mm-per-ms=69mm, or let's just say 7cm which is easier to understand. That is less than three inches.

Considering your fastest box also has some latency, you would only be interested in the latency difference and without knowing exact specs let's assume you can just divide it in half. So the latency difference would be approximately 3.5cm (or 1" and 4/10).

As he ^^ said, you only need to be concerned about stereo pairs. Always use the same box for both sides. Always, no exceptions. Even if the boxes are of the same brand and model.

[JFreak]

Originally Posted by martthie_08

DSP Plugins add latency

Yes!

People really don't understand that in the olden days of blazing fast TDM systems the real world mixer had roughly 350 samples of plugin latency, and somehow artists had zero trouble monitor themselves through it. But now they complain about 64 buffer and demand 32. Sheesh...