Re: Logic Pro Aggregate Audio Device
Jun 20th, 2011, 04:56
Thanks for reiterating the descriptions of what we're seeing here. It's almost 5 AM and I'm a bit loopy tweaking strings, so, like "I knew that" LOL but I just couldn't quite remember...
One of the problems with aggregating devices that crops up is exactly what you're seeing here: a difference -- even a very minute one -- between the two devices being aggregated. It's almost as though (i.e., conjecture on my part) the inputs from the second device tend to lag behind the first device when they're aggregated. In other words, aggregation allows you to consolidate multiple interfaces, but the correlation (or resolution) between them isn't always perfect to the letter.
The other possibility (again, conjecture) is that there's a slight difference in the A/D processing times between the first and second units. I'd be curious to see if swapping them around and then repeating the test produced the same 1-sample-off result.
But whatever the case may be, and all my conjecture aside, my main point in having you test these things out was to see IF there was indeed any timing differences between the units. I think the key here wouldn't be to worry so much about the 1-sample difference between the units as it would be to just make sure that anything that needs to be phase coherent to the letter gets recorded on one unit. For example, if you were to record a rhythm section ---- 8 drum mics, 2 guitars, bass, 2 for piano, 3 on the organ player's Leslie, that's 16 inputs all on one unit for which you know that all the inputs will be phase coherent to-the-sample. If your scratch vocal is coming in on input #1 of the 8-input unit, well, he/she's going to be one sample off from everyone else. Probably not enough to worry about.
Now... if worse comes to worse, you can always shift the 8 tracks from the 8-input unit back one sample in the arrange page once you're done tracking. But I have the feeling that as long as you know what the discrepancy is, you'll be able to select inputs accordingly so that you won't end up with phase anomalies when tracking all 24 at once.
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