[sdiy] Mystery synth sound

[rburnett at richieburnett.co.uk]

Hi synth fans,

I'd like to pick your brains about how a particular synth sound was 
created...  I've always liked this sound that features on a number of 
Jam and Spoon tracks (Rolf Ellmer & Markus Loffel) from the 90's and 
early 2000's.  It sounds like a resonant lowpass filter sweep but there 
is something else to it, and I've never heard anything quite like it 
anywhere else.  The resonance seems to have a dirty and distinctly harsh 
"scratchy" sound to it which I think works nicely in the genre they used 
it in.  It appears all over their album "Tripomatic Fairyfales 2001" 
like it's their trademark sound!  I'd love to know what piece of kit is 
used to produce this sound if anyone knows?

I'm guessing it might be the result of filter FM or some kind of 
overdriven digital filter, but I've never managed to get anything like 
this out of any of my filters, digital or analogue.  Or maybe it's some 
post processing like decimation, although it doesn't sound quite like 
aliasing to my ears either.

The best example I've found is at the start of "Follow Me":

https://www.youtube.com/watch?v=UfR7o8NI2W0
The synth starts at 0:00 and is initially quite smooth and clean 
sounding while the filter is closed down, but gets really scratchy from 
0:30 onwards as the filter opens up.

There are other examples in "Tripomatic Fairytales 2001" too:
https://www.youtube.com/watch?v=vvf4wwDpaCw
The synth starts at 17:35 but getting scratchy from 18:20 throughout 
that song.
The synth starts on another track at 49:00 but getting scratchy from 
49:10 onwards to the end of that song.

Any ideas?  This has been bugging me for about 20 years, so I'm all 
ears! ;-))

-Richie,