replacing a 12db filter for a 18db (or adding one to the system)

[jh]

???

Calling a filter that has (approx.) 18dB/8ve slope in the "interesting"
region a "18dB filter" is perfectly right. (And was introduced as such in
the EMS VCS-3 manual.)

JH.

-----Original Message-----
From:	Tony Allgood [SMTP:oakley at techrepairs.freeserve.co.uk]
Sent:	Monday, May 24, 1999 9:59 PM
To:	synth diy
Subject:	Re: replacing a 12db filter for a 18db (or adding one to the system)

I REALLY _LOVE_ that original tb 18 db filter)
(the 309
has 303-type waveforms, so that's okay, but NO 18db filter)

Hi Joel and all,

Sorry the TB303 does not have a 18db-oct filter. It has a bastardised 4
pole filter with 24db-oct for some of its falling response. However, its
roll off appears to be changed by the cut off frequency because of the
unbuffered cascade of CR elements. Part of the sound comes from its
unlinearities in the pass band as well as its behaviour at higher
frequencies. However, I do take your point that a 12db/oct, a la SEM,
does sound different, but not better, to the TBs filter. But is'nt the
309's filter digitally generated? So I suppose it wouldn't sound the
same. As for the waveforms... the TB's square generator is really quite
odd at low frequencies. I bet that isn't modelled on the 309. But if you
want the TB sound... shameless plug coming up.....

http://aupe.phys.andrews.edu/diy_archive/schematics/oakley/


All the best,

Tony