Stange recording speed issues in logic 9

[patlang12]

Hello. I'm encountering a strange issue in Logic 9. I've been reamping tracks through my guitar amp to add spring reverb. To avoid grounding issues I've had to do this in a roundabout way. I take the track I want to add reverb to, solo it, and bounce it to mp3. I take the mp3, put it on my ipod and play it through the amp. I record the track playing through the amp back into logic on a new track. Then I line up the first transient of each track. They play in sync for a while, but within about 2 minutes the reamped track has drifted noticeably ahead of the original track. I think it could be an issue the the computers internal clock? I've heard of issues syncing when recording on different devices, but the original track and the reamped track were both recorded through the same interface onto the same computer into the same logic file. I don't know if it makes a difference, but the original files were recorded about 9 months ago. Any tips would be very much appreciated. It's driving me crazy!

 

Logic 9.1.6

OS 10.7.2

MacBook Pro

2.4 GHz Intel Core i5

4 gb ram

Presonus Firestudio

[Eriksimon]

It is probably the MP3. Why do you bounce to MP3? Are you looking for issues and problems? Or are you looking to slowly degrade your sound quality by converting perfectly good audio to perfectly inaccurate, compressed, encoded (abused & battered) audio that is MP3?

First "rule of DAW": never use MP3 (or any lossy encoded format), always use PCM (= AIFF or WAV).

So, use an AIFF or WAV bounce instead. If that is still drifting, we can explore possible workflows to correct that - flex editing, most likely.

[patlang12]

I was bouncing to mp3 for the smaller file size. The loss in sound quality wasn't an issue because playing it through the guitar amp trashes the sound way more than the conversion does. Still you're right that I probably shouldn't work with mp3s. After I realized I could put AIFFs on the Ipod I tried that too because as you said there are a lot of issues with mp3s. I am getting the same results with AIFF. I also tried doing a realtime bounce instead of offline. None of these changes have changed my results. It appears that it drifts the same amount every time no matter what file type or bounce settings I've used. I have been messing with time stretching to get the files to be the same length. That is working somewhat, but I'd really like to find the root of this problem so I don't have to time stretch every time. Thanks for the help

[Eriksimon]

In my opinion the root of the problem is the difference in the clock speed on your Mac and the clock speed on your phone. Especially since the drift seems consistent. can you indicate how much it is? 1 second per minute? Or 0.1 seconds per minute? Or much more, or much less?

And what audio interface do you use?

[patlang12]

The drift is about .005 seconds per minute. Through a 4 minute song it becomes very noticeable by the end. My interface is a presonus firestudio project. When I try to record from an output of the firestudio or the headphone output of my macbook pro I always run into grounding issues which is why I've been using the ipod.

[Eriksimon]

I'd say you have two options: use flex (polyphonic, complex), or solve the grounding issues so everything can run through one clock only: the Presonus.

[ski]

+1

 

First, solve the grounding issues. They're almost always solvable. It could be something as simple as installing ground lifts on one or more devices. Whatever the case, it's absolutely worth taking as much time as necessary to solve that problem. And if you can't eliminate it entirely, you can usually minimize it 99% of the time. Second, always always always bounce to WAV or AIFF. Never use MP3's for production. It's just a big mistake, both for timing purposes and fidelity.