From analoguediehard Sent Wed, Nov 9th 2005, 22:39
From analoguediehard Sent Wed, Nov 9th 2005, 22:39
This does indeed work in practice. I know a well known monosynth that uses this technique successfully, although I can't say which one (and NDA is not a hip-hop group). The trick is when you sum the LPF and dry signals, the passband harmonics of the LPF have to be 180 degrees out of phase with the dry signal so that they cancel out. I do know that the passband output of a Moog ladder filter is out of phase with the input so you don't need a polarity switch. The levels on the mixer have to be adjusted so the dB cancellation is maximum. Also don't use resonance on the LPF unless your filter is the kind that does not attenuate the passband harmonics with increasing resonance (def not the Moog ladder filter). This technique dates back to the RA Moog days, neat trick on the modular. There's a REASON why some of the modules have complimentary outputs. MC -------------- Original message ---------------------- From: Mike Kent <xxxxxxxx@xxx.xxx> > > I have a pretty big 100m (8x191j, 40 modules) with 15 vcf´s and it gets > > pretty booooring > > sometimes with only lpf´s I can tell you, however that is going to change > > soon..... ;) > > You can probably get a HP or BP filter type of effect with your large > system, although you may need to make one special patch cable for it. > > If you send a signal into a low pass filter and then mix it back with the > original signal with reverse polarity, you can emulate a High Pass Filter. > > ______ ________ > | |--Polarity Switch--->| | > |VCO | _______ | MIX |----------> > |____|---->| LPF |-------->|______| > |_____| > > Or: > > ______ ______ ________ > |VCO |--->| |--Polarity Switch--->| | > |____| |MIX | _______ | MIX |----------> > |VCO |--->|____|---->| LPF |-------->|______| > |____| |_____| > > > One cable needs to have its wires crossed to switch the polarity. > > Add another LPF on the end of that chain to get a Band Pass Filter. > > It works in theory but I've never actually tried it. I just patch into my > Steiner Parker multimode filter to get HPF or BP. But this might be a low > cost solution if you've got all those modules already available. > > Let us know the result if you try this. > > Regards, > Mike. > > ___________________________________ > | xxxxxxxx@xxx.xxx | > | homepage.mac.com/mikekent | > |___________________________________| > |UU|UUU|UU|UUU|UU|UUU|UU|UUU|UU|UUU|| > ||||||||||||||||||||||||||||||||||||| > >