Further to Brendon's enquiry:
SARAH isn't custom hardware; it's a specific combination of off-the-shelf devices which, when configured in a particular way, produces a passable impersonation of the kind of free improvisation derived originally from free jazz - it's musically plausible but doesn't involve looping/playback or chaotic (random) responses.
SARAH works best with input that involves a wide range of frequencies, so AM is a highly effective instrument for the human co-performer to use. There's a short demo file here:
...which doesn't involve AM, just squirts of noise, but it gives a clear idea of what SARAH (here on 'soprano sax' - the standard MIDI patch) does.
There's also a relevant abstract in the draft programme for the SPEEC symposium - see link at the bottom of this page:
Thanks for your interest!