About the Classic Filter dB/Oct Settings

varice · Last edited by varice on Wed Jan 28, 2009 8:10 pm; edited 1 time in total

It is obvious that Clavia intended to emulate the famous classic Moog 24dB/octave transistor ladder low pass filter with the Classic filter module set to 24dB/Oct. But, I wonder about the Classic 12dB/Oct and 18dB/Oct settings.

Is the Classic 18dB/Oct setting intended to emulate the (in)famous classic Roland TB-303 18dB/octave diode ladder low pass filter?

Is the Classic 12dB/Oct setting intended to emulate the (in)famous classic Oberheim SEM 12dB/octave low pass filter? [EDIT: how silly of me, of course I meant to refer to the 12dB/octave filter sounds of the latter Oberheim synths, not the earlier SEM filter sound]

Or, are these just additional slope option settings for the Moog ladder emulation?

drapdap · Joined: Oct 11, 2004 Posts: 186 Location: bp Audio files: 1

Tim Kleinert · Posted: Tue Jan 27, 2009 10:44 am Post subject:

I once skimmed a paper that described modelling the Moog transistor ladder filter as a string of four individual 6dB poles with nonlinearities inbetween. This approach makes it easy to optionally tap the 12dB and 18dB as well. Hence I assume that Clavia took this approach. Rob mentioned that the Classic filter module indeed adds the first odd harmonic to the signal if driven hard. He exploits this nicely in a DIY filter design that uses the Classic filter in a feedback structure, thus adding the whole odd harmonic series in decreasing magnitude to the signal.

No, the Classic Filter in 18dB mode doesn't sound like the trademark Roland TB filter at all. That filter has a very quirky design to keep the resonance boost in check, which gives it its characteristic sound.

And the SEM wasn't a pure lowpass filter. It could sweep continuously from LP via BP to HP. IIRC, it was the OBX, the OBXa and the OB8 that had 12dB lowpass only, but the first one was discrete circuitry while the latter two were based on CEM chips -which makes it even harder to find similarities. Matrix12/Xpander: 15 filter types Laughing

-totally different ballgame.

iPassenger · Posted: Wed Jan 28, 2009 2:17 am Post subject:

Tim Kleinert · Posted: Wed Jan 28, 2009 3:28 am Post subject:

varice · Posted: Wed Jan 28, 2009 11:24 pm Post subject:

Hey guys!

róbert, Ross, and Tim - I thank you guys very much for your replies to my very (overly?) simplistic post. I really do appreciate your discussion and opinions!

Tim - thanks for correcting me about which model of the Oberheim synths had that classic 12dB/Oct filter sound... (not the old SEM, of course!)

What I did not mention in my topic question - is that my Moog MF-101 LPF also has a 2-pole (12dB/octave) setting, so I can easily do an A/B comparison of the G2 Classic filter 12dB/Oct setting vs. my moogerfooger filter! Twisted Evil

Reference to my G2X/moogerfooger LPF Frankenstein Monster:

http://electro-music.com/forum/topic-12266.html

So, I already have my own opinion about the G2 Classic filter dB/Oct settings that I will post here soon...

But anyway, would anyone else care to comment about the G2 Classic Filter?

varice · Posted: Fri Jan 30, 2009 1:17 am Post subject:

iPassenger · Posted: Fri Jan 30, 2009 2:37 am Post subject:

Blue Hell · Posted: Fri Jan 30, 2009 9:35 am Post subject:

varice · Posted: Fri Jan 30, 2009 10:54 am Post subject:

varice · Posted: Fri Jan 30, 2009 10:57 am Post subject:

iPassenger · Posted: Wed Feb 04, 2009 7:45 am Post subject:

iPassenger · Posted: Wed Feb 04, 2009 7:51 am Post subject:

egw · Posted: Thu Feb 05, 2009 9:59 am Post subject:

varice · Posted: Fri Feb 06, 2009 1:05 am Post subject: