What machine can do this please?

[Bruce Cassidy <bcassidy@iafrica.com>]

I want to record on site (not in a studio) for a half hour period and be
able to loop at various intervals what is happening and build this up into 
a
montage and shape it continuously. I would like to change the level of any
loop and add effects (not so imperative). Also I would like to be able to
replace or delete any loop on the fly and slide it around perhaps and
perhaps even change the length of it. I don't need a half hour of memory of
course just the ability to keep shaping the audio material continuously.

The loops should be able to be of different lengths and not necessarily all
nested within one loop. I am very used to hard disk recording but don't
think I can get any program I know to change tracks and go in and out of
record without stopping.
What is the machine I need please? Or is there one?

Thanks 

Bruce