Dual SVF Tuning

Is the tuning process of the dual svf the same as on a smr 4 board ?what is the best way to accomplish it ? First filter #1 then filter #2 ?

oh and by the way, there’s a BOM error…we need 6 8DIP sockets, not 5



  • Kill all oscillators
  • Set filter 1 resonance to 63, cutoff to 63, no envelope modulation
  • Adjust the filter 1 V/Oct trimmer so that the sound is not out of tune when you play a scale
  • Adjust the filter 1 range so that the sound doesn’t get too weird/distorted when the cutoff is set to 127
  • Move back filter 1 cutoff to 63
  • Set filter 2 resonance to 63, cutoff to 63
  • Adjust filter 2 V/Oct and range so that the two sounds (self-osc from filter 1 and from filter 2) are in unison


No way I can have a unison when both filters are set to 63 (cutoff) 63 (reso).

I don’t get beating sound if cutoff#1 is set to 59 and cutoff#2 to 62…Are these values acceptable ? If not, I might haven’t understood the way to use V/oct and range of filter 2



Ah, I forgot an important detail: you need to set in the modulation matrix note > cv1 > 63 so that the second filter tracks the note played on the keyboard too.

There’s no right or wrong value. It’s better to have filter 1 self osc track the note played on the keyboard ; and the range set in such a way that you don’t get harsh HF distortion when cutoff and resonance are set to high value. That’s all.

Ok, the modulation matrix info could be a good clue…I’ll test that in the afternoon !



I’m just trying to tune the filters on my SVF. I must say, trying to get the two filters working in unison is maddeningly difficult. I’ve never had a great ear for tuning, unfortunately, and I’ve been tweaking those four trimmers for about two hours now, and haven’t got any nearer getting the two filters to track in unison than when I started.

@pichenettes you say there are ‘no right and wrong values’- there clearly are, if the objective is to get both filters to track octaves and both be tuned to the same note…

Grrr… annoying. I’m going to bed now, anyway, with dissonant resonances (!) still ringing in my ears…


it should work. just tune one filter until you’re ok with it and won’t change it anymore (including octave tracking, with the help of an oscillator switched on)
then use the same settings for the second and try to match the resonances at 63 with cutoff full open. maybe compare at different lower pitches to adjust a little.
after that the octaves. if there are some small differences you just need to find out if they are related to the octave behaviour (changing with different notes) or resonance.
it’s not so easy, that’s true. i’ve also continued tuning and trying again and again. also not finished yet, as i still have to replace the ceramics with styroflex, and do the zener switch. after that i’ll try to tune it again.
but at one point i had them pretty close, and it sounded super fat.

I’d imagine it gets fatter still if the self oscillation is tuned an octave or so apart for the filters?
I’ll have to get one, once I have recovered from this last episode of self sorcery :slight_smile:

If you want the filters to sound one octave apart, you can just set the second filter to a different cutoff value. You don’t have to mess with the trimmers to get that.

True! I completely forgot they would be independently controlled.
I really should quit the lead free solder intake. I don’t think it agree’s with me…

I couldn’t make the 2 filters play at unison. The problem was that the range of filter #1 was set too high (low ?)…setting it a bit higher helped me have no beating sound when tuning filter #2

@Tom so you did get them tuned so they played in unison in the end? Or not?


Yes, I finally managed to hear them playing at unison !

Good news, Tom, and thanks for the tip. Gives me hope I might get mine tuned too, eventually.


I’m realllllly not getting this. Any now I’ve fiddled with the filter 2 v/oct trimmer for so long it’s stopped working :frowning:


Have you tried to modify a bit the filter #1 V/oct. This is what made my SVF play at unison…

i have ended to tune it… my trick is: use a tuner, like chromatic tuner(free and usable demo) on osx: tune the v/oct and range of the first. look what note you have with the tuner. shut the first filter.
trim the second filter v/oct, then when v/oct is good, just trim the range to the corresponding values you have looked of the first filter.
It’s not so difficult: i have the unison (a sort of lfo which double it’s speed whith each octave), and i think it’s good like that and not so difficult! ( hope i am right in this method)…

I dug up this thread and noticed that maybe some fellow Dual SVF owners had never completely tuned their filters correctly so I wanted to share a trick pichenettes mentioned on a different thread.

Instead of 1 mod matrix entry set to 63, you need 2 entries set to 32 like this:

1, note, cv1, 32
2, note, cv1, 32

This will make tuning much simpler as the filters will track exactly the same across the keyboard. With the 1-mod setup you’ll tune 2 notes to match, but you’ll find that notes in the middle still won’t match, tempting you to keep fiddling and fiddling and fiddling…

I’ll give that a go! I never got my SVFs tuned correctly. Actually, I wrecked a trimmer trying. I fiddled with it so much it eventually just stopped working, and I had to desolder and replace it…