Back a few months there were a couple of mentions of the Sequential DSM03 Feedback module, and how there was very little information out there about it.
I won one almost accidentally in a charity auction (I expected to be outbid and wasn’t) and it arrived yesterday. I’d summarize it as “Karplus-Strong in a module” but with some extra applications. I was expecting more of a general “resonator” feel, but it’s not really that.
It’s got a white noise generator with an AD envelope (and unfortunately no way to keep the noise going continuously without retriggering, which has some consequences that can admittedly be pretty interesting for the noise texture). There’s no separate noise output.
That, plus an audio input, feed a short delay. The delay can go just long enough for rapid echoes but is more suited to Karplus-Strong; it tracks 1V/octave without any ugly slew and is capable of covering a good few octaves.
There’s a lowpass filter in the feedback path for the delay, but unfortunately increasing resonance, or lowering the cutoff more than a little, very strongly suppresses the feedback. I really wish that was compensated, and/or there was just more feedback gain to work with (which would also allow longer echoes at lower speeds). If using the noise generator, the noise is still very much audible in the output, and there’s no wet/dry control. The filter can throw off the pitch tracking a bit but in a way I like pretty well honestly. Modulating the feedback amount and/or delay line tuning both work very nicely.
Overall it sounds pretty nice. I haven’t tried it just for the filter, nor experimented too extensively yet with processing oscillators, or supplementing the feedback externally. Self-patching the output to the noise envelope trigger input can be fun though 
With two Rings, Mimeophon, Supercell, Filter8 and Ripples in my system already, it feels like I should already have this well covered… and yet kind of maybe not…? At the very least I’m going to hold onto mine and keep playing with it until the SynthTech E520 ships, and see if it still feels interesting. I feel like it’s one of those modules that might serve me well on its own merits, though it’s not really what I was expecting when I bid on it.