Question about PT LE latency w/ outboard gear

[skybluerental]

my question to all of you is this:

i like to print outboard compression on new tracks while i am mixing using my Pro Tools LE system. i hae an apogee rosetta 800 hookd up to it via ADAT to a 002 and all the D/A and A/D goes through that.
so, my question is, what is the exact amount of latency that will occur during this process. i would like to know so that i can just automatically nudge the track forward in time that amount every time.

i called apogee tech support and aksed the guy how much latenecy would occur in this situation and he said he didnt know....................

SURELY someone from apogee or some smart guy here can answer my question and make life a lot easier and sweeter sounding for me!

thanks
anthony gravino

[theblue1]

I'm guessing he didn't understand the question. [UPDATE: I was thinking "he" here was a Digidesign support guy but a sharper-eyed pal hipped me up that it was an APOGEE support guy. So, you know, he should be up on Apogee issues, for sure, but I guess he can be forgiven for being less so on PT ish.]


Since your compressor is, presumably, an analog device, we can assume we don't have to compensate for any latency from it.

So, therefore the only latency we need to measure is the time it takes for a signal to get out of Pro Tools LE and through your converters out into the analog world and then turn around and come back in through the hardware into your track.

Of course, it bears remembering that EVERY overdub you do involves this particular latency, since what you hear (what's coming out the converter's DA output) is your time reference for laying in overdubs.

At any rate, it's pretty easy to calibrate this -- but remember the amount of time the converters take changes with the sample rate (although it's not absolutely proportional in most cases), so you need to recalibrate for different sample rates.


The typical calibration is the so-called "loopback test" and it's easy.

Just connect one of your analog outputs on your converter to an analog input. (Make SURE you do not have "input monitoring" turned on or you could end up with a supernasty feedback loop.)

Now, take a sound with a sharp, easily identifiable transient (typically a "ping") and play that out your looped patch cord and back into an input, recording the analog copy of the ping.

Now, by zooming in, locate the exact sample value of the original ping and the exact value of the copy. The difference between these is the "tracking misalignment" between existing tracks and new overdubs.

ANY overdub will be subject to this misalignment unless otherwise corrected.

Since the misalignments are typically not huge amounts, you may not notice it. IIRC, an 001, being PCI-based, has a very short misalignment, less than 2 ms, I think. Th 002 and Mbox (especially) have considerably higher misalignments.

With overdubs the issue is whether or not this misalignment is a musically significtant value (and then there are us sticklers who think that everything should line up, period).

But with effects sends/returns you may end up blending dry with returning wet (not as likely in the case of a compressor, of course) and that may cause phase issues.

In the ASIO world, audio drivers are supposed to report their hardware latency and many DAWs try to use those reported latencies to compensate. But in actual testing, it appears that this compensation often leaves quite a bit of accuracy to be desired, so many DAW makers have begun offering some form of individualized compensation that can be adjusted to breach the gap.

Mackie Tracktion has an automated ping loopback calibration. I understand that Cubase/Nuendo has such an automated comp but there seems to be debate about how well it works. Cubase users may still have to tinker their numbers even after calibrating, according to some. And -- according to some reports -- Cubase's automated compensation doesn't work when a driver has a "negative offset." (It reports a false value that makes compensation try to push it too far forward.) Sonar (and Logic, I'm told) both have manual compensation slots where you can enter an adjustment value after you have "hand calibrated" it with the loopback test described above.


So, it appears that these unadjusted for or poorly adjusted for hardware latencies affect many of us to varying degrees and at least some of our DAW makers have tried to give us the tools to compensate for them -- but that they don't always work as well as we'd like -- when we have them at all.

And, of course, the very same latency that affects the round trip of audio going out into the analog world for external FX loops and back in is the same latency that will affect any overdub/new track in relation to previously recorded tracks.



PS... the reason I say the Digi tech support probably didn't understand your question is because I ORIGINALLY became aware of this whole issue by reading complaints on the DUC (Digidesign User Conference bb) about tracking misalignment with 002s and Mboxs when they first came out. It's not exactly news. (I was feeling pretty smug until I tested my own PCI based converter at the time and found an approximately 4.5 ms misalignment! At that time, my DAW didn't even have a sample-value accurate nudge command so to compensate I would have had to calibrate a MIDI tick value for each tempo and adjust by that. I chose to ignore the gap but when I switched to a MOTU 828mkII whose WDM/KS drivers had a nearly 8 ms misalignment, I simply had to get proactive. I recognize that that's the time it takes sound to go about 7 feet [correction: make that about 9 feet. Wasn't awake yet!] but it was, nonetheless, throwing off my timing in some stuff, particularly hand percussion.)

[NickH]

This will sort you out:-

"Pro Tools LE™ Latency Chart"

Pro Tools LE Tracking Latencies Charts

Cheers

N

[theblue1]

Where were you a couple hours ago?


I bookmarked it, too, for future ref.



[A quick scan of it also reminded me that I'd airballed my speed-of-sound calc improrperly and written 7 feet when I meant 9.]

[madcowvt]

Originally Posted by NickH

This will sort you out:-

"Pro Tools LE™ Latency Chart"

Pro Tools LE Tracking Latencies Charts

Cheers

N

Very cool indeed. Thanks for that!

[skybluerental]

Originally Posted by NickH

This will sort you out:-

"Pro Tools LE™ Latency Chart"

Pro Tools LE Tracking Latencies Charts

Cheers

N

thanks!
so then, just to clarify this................

if i am using my 002 w/ low latency monitoring, buffer set at 1024, the latency will be 87 samples or 2561 @ 44 k????

seems more like 87 to me!
: )

thanks again.
adg

[max cooper]

Do you know what Low Latency Monitoring is?

You guys are looking at the Tracking Latencies when you should be looking at the Mixing Latencies:

Pro Tools LE Latency Chart - Mixing with Analog Gear

[skybluerental]

Originally Posted by max cooper

Do you know what Low Latency Monitoring is?

You guys are looking at the Tracking Latencies when you should be looking at the Mixing Latencies:

Pro Tools LE Latency Chart - Mixing with Analog Gear

yes i do know what LLM is.
however, i still feel there is latency when i print the analog effects onto a new track even using low latency monitoring. if i solo up the affected and unaffected track, they seem to phase a bit.
surely there is a small amount of latency that occurs in the D/A A/D that happens when you print analog effects. i just want to know what that number is............

[NickH]

It also depends on the plugins as well, how much latency is reported on the source track when you CTRL click the volume readout?<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p>
<o:p></o:p>
PT will automatically compensate in some circumstances (and no, I am not taking about ADC)

If I remember correctly there is around 7-8 samples difference between my apogee Rosetta 800 & the 002’s round trip…<o:p></o:p>
<o:p> </o:p>
You REALLY need to do a quick loopback test as described in the posts above if you want to be certain on the Rosetta… it would only take a few mins… <o:p></o:p>
<o:p></o:p>
<o:p></o:p>
N

[theblue1]

Originally Posted by skybluerental

yes i do know what LLM is.
however, i still feel there is latency when i print the analog effects onto a new track even using low latency monitoring. if i solo up the affected and unaffected track, they seem to phase a bit.
surely there is a small amount of latency that occurs in the D/A A/D that happens when you print analog effects. i just want to know what that number is............

Yeah... I read this page earlier but I don't think there's anything inconsistent there; he gives you the time values that tested out on his system for that loop out.