@porres
It is based on this talk by Geraint Luff:
However, the basic structure is the same as in rev3~, early reflections are fed into a 16-channel fdn. Delay times are selected from a table of prime numbers. The "secret" lies in the mixdown of the 16 fdn channels to stereo. It was more or less trial and error, adding and subtracting the signals and listening what sounds good.