Getting the 303 sound, is more about "getting the classic acid 303 sound".
I had one in the 80's and thought it was crap, due to the fact that i
was trying to make basslines (it was after all REALLY called the
Roland Bassline) and it was only upon the arrival of "Aciiiiiid" that
I went OH MY GOD.
SO yes 20 percent is the filter (But in my humble opinion you can do
it with any high resonance setting on almost any filter)
20 percent is the slidy sequencer thing...
but 60 percent of THAT ACID SOUND is distort the shit out of it!!

Yep.. easy as that, take a square wave into a filter, (no modulation
or adsr modulation please) set Q high but NOT quite oscilating, and
distort. with a fuzz pedal, or modular equivalent. Now, grab that freq
control and twist... Aciiiiid!!!
you will never get exactly the right sound without a 303, but you can
get the same effect with anything and a fuzzbox!!!

IMHO of course


mark

--
www.markfrancombe.com
www.looop.no