[sdiy] filtering cv

[Scott Stites]

Hi Gregory,

I read a post from Cynthia Webster on a different forum (can't remember which now) about the Low Pass Gate.  According to Cynthia, if you eliminate the 1 uF input cap, the LPG can process CV's in the low pass mode and actually act as a lag generator.  After all, a lag or (or slew generator, portamento, etc.) function is really just a low pass filter with a really low cutoff.  Varying the cutoff of the filter should determine the time constant of the lag.  So, if your LP filter is DC coupled, or can be DC coupled, it should give you varying amounts of slew, depending on the cutoff.

I've actually been beta testing some designs for Thomas Henry - he's coming out with a killer DIY book sometime before Christmas, and I'm lucky enough to be beta testing some of the circuits to see if they fly.  This particular filter has an AC/DC switch input switch, with one purpose of the DC switch being to allow the filter to process CV's.  And, guess what?  I haven't even tried that part of it out yet (some beta tester, huh?) - I've been so busy just enjoying the filter itself - super sweet.  But, I digress.  This filter also provides quadrature outputs in self oscillation, so that's another bonus to consider/search for when deriving control signals from a filter.

Cheers,
Scott


-----Original Message-----
From: gregory zifcak <zifcak at hotmail.com>
Sent: Jul 14, 2004 5:54 PM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] filtering cv

what happens if you patch an analog sequencer through a resonant low-pass 
filter to the pitch cv input of an oscillator? i'm assuming that depending 
on the cutoff, the change would be slewed, giving a portamento effect. then 
what happens if you turn up the resonance? what does the change sound like? 
what about self-oscillation? what would the sequencer output look like?

sorry for the lack of diy. just suppose they are homebuilt modules:)

greg

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