Latency Compensation.... Am I understanding this correctly?

[jgrif08]

I was reading a thread on another forum the other day about phase issues. someone mentioned using latency compensation to help avoid phasing problems caused by plug ins (I think specifically he was talking about EQ and Reverb plugs). Based on my understanding of phase issues, latency compensation would basically only help here if say, for example, you were running a vocal track to reverb through a bus. Since part of the signal would be going straight to the outs 1-2 (for arguments sake) and the other part would be delayed very slightly before reaching outs 1-2 (because it is bussed to reverb first), this could potentially cause phase issues (correct?) If so, how would I go about using latency compensation to fix this?

On the flip side. If I am using reverb, or any other plug for that matter, simply as an insert on whatever track there should be no need for latency compensation (in so much as it pertains to phase issues) correct?

If that is the case (and my understanding of this issue isn't completely off base, then what are the other uses for latency compensation? I never really use it as I have never run into any issues with latency on my current setup. Am I missing the point here? Is latency compensation something I should be using regularly?

Thanks for any input,
J

[Geert van den Berg]

You've understood latency compensation correctly.

But I'll give you an example where compensation is always needed. It is in a multi-mic situation where latency can really affect the sound of the mix. Usually this is with drumtracks. The snare is recorded in a certain phase to the overhead mic's. Now if you put an EQ on the snare track and it has a slight delay, even of a couple of samples it will change the phase relationship, it doesn't mean it's now automatically out of phase, but it's just that the phase has changed. It could be for the better but most of the time it's not, and if there's no way your DAW can do this automatically it's quite a task to keep track of everything and you should exactly know how much delay every plug is causing.

If let's say the bass and the guitars weren't tracked in the same room and not at the same time, but via overdubs, then putting on a plugin on of the channels doesn't cause such a critical difference as with the prior example.

[jgrif08]

thanks for the input. Im wondering if you might be able to address another issue I was wondering about that is related. Lets say for example im working on a song that has a couple tracks of guitar, a simple bass line, and two tracks of vox (one is a backup vocalist). If I insert a compressor and an EQ on just one of the vocal tracks (just a theoretical situation), and leave the rest alone. Latency compensation will most likley not be warranted here right?

Im getting the impression that phase issues occur more during the tracking of the song than anything else. In the situation above nothing should be out of phase (bearing in mind that the two vocal tracks are actually two different parts and not two mics on the same part). I guess I'm just wondering this: Simply put, should I be using latency compensation every time I use plug ins?

[Geert van den Berg]

The short answer to your question, you're absolutely on the right track!

The long answer:

What software are you using?

Ultimately you should always use latency compensation, but...

if you put these plugs on this vocal track, do you hear a difference in timing if you put them in a flat non-working position? Probably not, as it's probably just a couple of samples and that's just too little of a difference...

So in general I wouldn't worry about it.

However there some plugins which consume a lot of CPU cycles (for example Waves Linear Phase) putting one of these on a channel in for example PT LE and leaving the others alone, would cause too much timing difference.

And if your software doesn't support ADC and you do have a multi-mic'ed source the solution could be to put the same plugins on every track, doesn't have to mean that you're adding processing to every track, just leave them set flat and adjust the tracks which need it, though this can consume quite some resources. Another option is, let's say I want to put the same EQ on 2 guitar tracks, to route it through an aux channel and put an EQ on that aux.

There are several points when digitally recording where latency can occur, but the cause is more or less the same. It's not only during tracking that latency can cause problems, though it's mostly noticed when tracking, because in the past the software buffers couldn't be set low enough before the CPU chocked, causing delays which were too big to monitor live through the software. Nowadays this isn't such a problem and there are also soundcards with hardware routing available. But the software buffer still plays a role when putting plugins on recorded tracks, the latency will be bigger if the buffers are set higher.