Filter-calibration tool for Shruthi 4free by TubeOhm

Hi, i build a easy to use filter calibration tool for Shruthi. It is a frequency counter. This tool works standalone (PC only)
Connect Shruthi to your ASIO card ( input), make the setup in the standalone version Devices> wave >> your Asio card.
Then set up your Midi output device in >> devices MIDI and connect Shruthi to Midi.
Execute the Filtercalib.exe, The settings for Shruthi filter calibration is give by Olivier. ( Osc’s to off, Reso max, Adsr to off)
Click C3, and see the resonance frequency. Click C4, the resonance frequency must be double, if not adjust the poti.
If you have any questions , contact me.
Direct download link.
Copy this link into your Browser, the DL start direct.
Hopy you will find it usefull.



1 Like

Thanks for this Andre’

here a small video.





Excellent work!

Useful thank you

Two questions:
In the video the value for tuning c3 is around 0.294, this is what we must do on our shruthi, or is it just for the example in this particular case?

Does it work the same for tuning the Ambika voicecards with this tool?

Thank you

It’s just an example for this particular case.

You should tune so that playing octaves (say C2, C3, C4) will display numbers which are exactly the double of the previous. We don’t care if it’s 240, 480, 960 ; or 270, 540, 1080 or whatever. Or playing 2 octaves (say C2, C4) will display numbers which are the quadruple of the previous (say 240, 960). Actual values are not important since most recent products don’t have an offset trimmer.

Personally, I find a frequency display rather useless for tuning V/Oct settings. I am currently developing a tool used for factory calibration of upcoming assembled products, and it displays the ratio between the last stable frequency and the current frequency - so you tune the filter by making the device play C2, C4 ; and tune the V/Oct until it shows 4.0.

Hi, first it is for free and i think it is a small help for people without a scope or a frequency counter. But Ok, i have build Filter calib 2 , a frequency counter with a second function.
This second function ® steps Shruthi from oct 1 to oct 2 to oct 3 with Midi and calculates the ratio between oct 1 and oct 2 , oct 2 and oct 3, and oct 1 and 3. It shows also the linearity between oct 1/2 , 2/3 and 1/3 in % , basic calculation is ratio. Lin below 100 % means , the resonancy is less than double, above 100 % resonancy is more than double. Precision /- 1 digit . Ratio for oct 1/2 and 2/3 should be 2/- and between 1/3 = should be 4 .

Same settings like the first version.

it is also 4free and the same download link- same settings. Include a small osczilloscop.


Now that’s a great improvement!

great, i will try it on my mac with parallels tonight!

Damm ! This will become incredibly handy when i rebuild my SMR4 mk1 & finish my Polivoks… Awesome !
Thank you quite a lot good sir ! :’)

Sorry PC only, no Mac. But maybe it works with V-Machine VFX host software on MAC. let me know.

V’cent, there’s no filter tuning pot on the Polivoks.

@tubeohm it works perfectly with parallels desktop emulating windows xp

Parallels with what ? Man, this makes me shiver brrr
Works with Bootcamp and Win7.

@deadmonkey meh, then just my smr 4 ^^
Shows you how much I have studied the polivoks :confused:

I have test it, works also for Ambika.

i have a question about filter calibration : i used the filter calib, it’s usefull, i calibrate the shruthi : 2.250Hz, 4.5Hz, and 9Hz. But a thing make me disapointed, the sine is not stable , i mean, the frequency change everytime, not a lot but i sound like going from 9000 to 9020 in maybe 25s, it is normal as there is fluctuation ? maybe cause of the stabilty of the filter ? or heat ?

But 9khz is totally on the edge of the musical spectrum.
Try if it is stable between say 50hz and 3200 hz that’s already 6 octaves

and 20 hz on 9khz is less then 1 cent tuning difference… Not something you can even notice by ear.


If you want a more stable Filter use a VA Synth. Your expectations are a bit exagerated, this is real world here…
And: go measure a MiniMoog. See?

it’s really good like that, i just want to know if it was normal ! It’s really stable at 2250Hz, and to be honnest, the Lp2 yellow magic is the filter i prefer actually, it’s really dirty as well ! i just start to use it with my SEQV4 yesterday (first time :slight_smile: ) and it’s just so gooooood !