Recording without MOTU interface, Aggregate device woes

[papageno]

Hello,
I am posting a newbie question here (mainly because I am a newbie). I did some searches before starting this thread so please just point my nose in the right direction if the issue has been covered here.

I have to make stereo recordings on location and I have the following gear:
Stereo mic setup, Audient Mico, UltraLite mk3, MacBook Pro 6,2.
SW: DP 7.24, MacOS 10.7.3

I used to connect Mico with coax S/PDIF to UltraLite and use Mico's clock as a master. This all could be selected in DP and the setup worked like a charm.

However, I would like to remove UltraLite from the equasion when recording live concerts on-location. I connected Mico's optical S/PDIF output directly to MBP. I then created an aggregate device in Mac Audio/MIDI setup app, using digital input as a clock source:

When I did this, the setup app automaticly selected "drift" checkbox for Built-in output. This resulted in a digital noise. When I deselected "drift", I started to hear occasional clicks when playing back test recording in DP. The clicks appeared randomly so the recording itself seems not to be affected but of course I am not 100% sure that it cannot happen while I am recording 1 hour at a live concert.
The first big question is:
"What does the "drift" option exactly do in Apple Audio/MIDI setup app's Aggregate Device setup?
Apple, weirdly enough, does not provide any useful info on the topic. The drift checkbox has just been left out from the help. What exactly happens if drift is selected on input or output or none or both devices?
The most important thing I want to acheive is:
to get a recording without clicks, using Mico's clock (it appears to be much better) and not having digital noise coming from clock issues in the file.
I will do all necessary cutting and editin later, using UltraLite at home, all I care about is undistorted material on HD.

[NazRat]

In DP you can select multiple devices in Hardware Setup by cmd-clicking them. You don't need to use an aggregate device - try that. Not sure about what the clocking options will be.

[papageno]

In DP you can select multiple devices in Hardware Setup by cmd-clicking them. You don't need to use an aggregate device - try that. Not sure about what the clocking options will be.

Will try and report back here later. Thanks.

[mikehalloran]

Don't use another clock source besides the Apple internal. More and more manufacturers who don't make clocks are recommending this. If this works - and it should - then you can start messing with the settings to see what does and doesn't work with your new setup.

[papageno]

Don't use another clock source besides the Apple internal. More and more manufacturers who don't make clocks are recommending this. If this works - and it should - then you can start messing with the settings to see what does and doesn't work with your new setup.

Yes, that is the point. I want to leave Apple internal clock completely out and sync everything to Mico's clock. In case one connects Mico to a Mac via Toslink cable, there is no other way. Mico's clock has to be master in this case, othewise there are 2 parallel clocks and sync issues will be inevitable.

I followed the NazRat's suggestion and skipped Apple's aggregate device. So far no clicks but I have to test this more extensively.

Still I am pondering what does the "drift" checkbox do...

[papageno]

Did some longer testing.

Conclusions:
1) selecting input-output in DP hardware setup and trying to sync stuff to input- no go. Every few minutes DP puts up an alert that some audio was skipped. I suspect that somehow the mac clock and mico clock work in parallel and therefore get timing errors.

2) aggregate device seems to work if no "drift" checkboxes are selected. Will listen to recorded material carefully in studio tonight. So far I have heard no problems but better speaker system could still reveal some clicks.