Initially I thought that null tests would be meaningless but given your interest Mike, I got too curious and delved in just for fun.
Here's a zip archive I prepared that contains a Reaper project (DAW can be freely downloaded and tried from http://www.reaper.fm) with associated audio files. These are the original AIFF loop and the Mac audio recording I posted before.
I created four tracks:
1. the original AIFF loop
2. the original AIFF loop again
3. the recording from Apple Loops Utility
4. the recording from EigenD
This is the starting point:
* track 1 is the only one that's not muted
* track 2-4 are muted and have their phrase inverted
I aligned each track sample-precise on the first very spiky transient with a marker that's named 'Sample Sync Point' in the project.
Before continuing, you might have to Reaper's Options menu, select Preferences and choose the audio interface you want to work with.
Proceed like this to go through the test:
* play the project as-is and listen to the first track
* this is just the original AIFF file automatically repeated by Reaper
* un-mute track 2
* play the project
* you should hear nothing as both AIFF files are nulling each-other out, since they repeat in exactly the same way, the nulling continues until the end
* mute track 2
* un-mute track 3
* play the project
* you hear transients bleeding through and it gets progressively worse
* the Apple Loops Utility doesn't play the original loop back in a bit-correct fashion
* the loop doesn't align up from beginning to end, it's time-stretched even when the bpm was the original 111
* the loop repeats are different from how Reaper repeats loops, which is ok, it's probably slightly crossfading at beginning and end
* mute track 3
* un-mute track 4
* play the project
* apart from a slight transient bleeding through at the beginning (crossfade), you hear nothing during the first loop repeat
* the second repeat you hear a few transients bleed through consistently through the loop duration
* the third repeat some more transients, but still consistent, etc ...
* this is EigenD that plays back the loop bit-correct with some slight crossfading as it repeats, which is what's causing some transients to bleed through as it repeats more and more
So this clearly demonstrates that EigenD actually behaves very well and plays back the loop perfectly correctly.
Hope this is helpful,
Geert