negative polar gain

Discussions on sound production outside the synthesizer such as mixing, processing, recording, editing and mastering.

negative polar gain

Postby Solderman » Sun Sep 01, 2013 4:56 am

I have noticed with my Moogerfooger MF-101 lowpass filter that the negative half of the output tends to not only have a more rolled off shape but is typically about 6db or more lower in amplitude than the positive half. I noticed something similar, but far less dramatic, with the output of a Prodigy, so it might be an anomaly of the ladder filter.

Question here is, is there a way in an audio editor to only change the gain of the negative half of the waveform without affecting the positive half? I can't think of anything short of some complex sequence of events, like copying the entire recording into another window, raising the DC offset to clip the entire positive half then lower it back, and finally add that to the original audio clip(perfectly in phase, of course) for additional gain.

"Lots of people are nostalgic for analogue. I suspect they're people who never had to work with it." - Brian Eno
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Re: negative polar gain

Postby optimus prime » Sun Sep 01, 2013 12:32 pm

Cool Edit Pro/Adobe Audition's distortion effect has that exact ability.

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Re: negative polar gain

Postby Solderman » Tue Sep 17, 2013 1:41 am

Seeing as that technique is limited to one editor I don't use, I've decided to give the offending sound clips a negative DC offset of 12db, normalize/limit the clip, then noise gate the silence gaps with a 10db threshold and at least a 90ms decay.

Also just fyi, I looked at a clip from an actual Minimoog, and the bias is inverted when compared to using the MF-101 with the MFB Kraftzwerg, so I guess the Kraftzwerg VCA input is inverting the signal.

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Re: negative polar gain

Postby Stab Frenzy » Tue Sep 17, 2013 11:45 pm

What you describing is typical from a class A circuit, the asymmetrical distortion is one of the things that makes it sound nice. Basically if you succeed in getting rid of it you'll end up removing one of the reasons you using the filter in the first place, just leave it.
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Re: negative polar gain

Postby Solderman » Wed Sep 18, 2013 5:13 am

I can appreciate that for quieter parts where the wasted headroom isn't as much of an issue, but if it needs more presence, then I don't mind processing it. I've done it several times so far and have not noticed any degradation. It just allows me to make it louder and it still sounds good to my ears. I don't do much approaching pure vintage anyhow. It doesn't have to sound like a 904a. It doesn't even have to sound like a Voyager filter. Just give me Moog squelch I can still rattle the windows with.

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