my guess...
for the wave generation, use a buzzy sawtooth (or maybe square wave?) and modify the pitch of the oscillator with an envelope.
then,
use a 'wetfilter'
it's basically a spectrum of bandpass filters each attached to a delay line. the lower frequencies have a shorter delay and then the higher frequencies get delayed more and more. (or it might be the other way round,,,,lower freq's delayed more, higher freq's delayed less...i can't remember exactly)