i went to guitar center and only got to play with the dd7 for a few minutes but couldn't figure it out completely on the hold function...

you start out by putting it on hold a and it turns green...
then you record some.

then you press it again and the light turns yellow.
it's looping what you recorded on green, and you can record more on top.

now it turns green again, and it's looping the last 2 things you played on top of each other

and i think you can loop a third recording on top.

then if you press it again, it goes back to red...

i believe that's it. can anyone clarify how it works?

i just found this video which shows some 3 level recording