Shruthi XT Dual SVF


i’m tweaking my brand new Shruthi XT Dual SVF for a few days now but am in darkness concerning a few things:

1/ the two independant filters can be routed serial (>) or parallel (+).

Some combinations mute the sound, others almost mute it, But i can’t see the logic (i’m no technician or sound engineer) when :

lpf > lp makes no sound at all
hpf > hp makes sound
bpf > bp makes almost no sound at all

why are the behaviours different when each mode is routed serial with a same mode ?
I found no info about this phenomenon… but again, i’m new to this.

And sometimes changing one mode won’t change the sound at all :
bpf + lp or bpf + bp sound identical

2/ There’s also the “<” sign after the main filter modes, what does it mean ? I found info about the 2 other signs (> and +) but not that one.

So i get for example bp < > lp = no sound at all, hp < > lp no sound at all.

3/ There’s also an option about linking the cutoff frequencies but if i’m right that"s somewhere in the mod matrix. I guess it’s that one ? :
Mod | src | dst | amt
1 | not | cv1| 63

4/I remember pichenettes talking somewhere about a notch mode that can be obtained by a logical trick (the settings of the filters), impossible to remember how, or to deduct it from logic and googling did not help me either.

Thanx in advance if you know something. I’d like to understand rather than random tweak those 36 combinations.

  1. I’m pretty sure there’s an assembly mistake that causes one of the filter to not work at all (or maybe a problem in the filter routing hardware).

  2. If you select lp> instead of lpf as the main filter mode, it means that filter 2’s cutoff control will become a relative cutoff (also known as “separation”) control instead of an absolute one.


  1. You no longer have to use the modulation matrix for linking the cutoff frequencies.

  2. You can do a notch filter with lp> as the first filter and +hp as the second filter.

Thank you again for the quick and precise reply pichenettes. I hoped it was not a hardware default but i’m so far from the wonderful timbres one can hear here … this really makes me sad. I’ll call the seller up. Thank you.

i called him over the phone. I will return the unit to him. He’s not the builder, he got it from Pharma.
It’s a gloomy thing that i cannot solve or check the problem myself… so i think it’s the best thing to do…

here the complete (36) results i wrote down on a paper yersterday :

lpf : >lp no sound at all, >bp almost no sound, >hp sound
lpf : +lp sound, +bp sound, +hp sound
bpf : >lp no sound, >bp almost no sound, >hp sound
bpf : +lp sound, +bp same sound as before, +hp sound
hpf : >lp no sound, >bp almost no sound, >hp sound
hpf : +lp sound, +bp same sound as before, +hp sound
lp< : +lp sound, +bp sound, +hp strong sound
lp< : >lp almost no sound, >bp almost no sound, >hp sound
bp< : >lp no sound, >bp almost no sound, >hp weak sound
bp< : +lp sound, +bp sound, +hp sound
hp< : >lp no sound, >bp no sound, >hp almost no sound
hp< : +lp sound, +bp sound, +hp sound

Thank you in advance pichenettes for checking if this confirms your prognosis.

i don’t have lp> , only the 36 modes i quoted before, maybe you meant lp< ?

Chiming in since I built the synth…

Actually 6 months old…

Well, everyone can make mistakes but I would have noticed the problem when calibrating the filters and testing the synth before shipping it.
And again, the synth has been built 6 months ago, the seller had it for 6 months and never reported any issue.
Then he sells it, SHIPS it and then there is a problem…
The fact it was shipped is quite important since a friend of mine experienced some issues after he received a Shruthi freshly built I shipped to him.
And it turned out that the Atmega had got slightly loose in transit making the synth behave strangely.
Once he pushed the MCU making sure it was well sitting in its support, he never had any issue after.
In this case, I’d make sure the 4053 didn’t get loose… or even bad.
Hope it helps.


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Hi O.T… i see C.B. called you up.

Not sure though, being a drummer in the first place, if he’d notice the filter’s malfunction. The synth works even with one filter out of service, and if one does not really pay attention and have time enough to spend on it, it may be overlooked - i don’t know. I suppose you know your job as for soldering, so it may have got damaged in either the first or second sending, it does not matter much which one though.

Should i open it, withdraw all screws and look if the part you mentioned is loose ? There are many screws ^^

Yes, C.B contacted me.

As I said in my previous post:

So, I’m pretty sure I would have noticed any problem.
Anyway, I would not recommend to open it since C.B agreed to take it back and he may not want to do it if you open the synth.
Also, we have a common friend living near C.B.
He knows very well Shruthi so it might be easier to fix it if C.B gets the synth back.
(And I will be able to help them)
If you really want to have that Shruthi, perhaps you could work something out with C.B.
Like he gets it fixed and sends it back to you.

I’ve been in the “synth world” for 30+ years and rarely came across people who were keyboardist in the 1st place.

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I just talked with the seller, he says not to have noticed if both filters worked or not, having used it only a very few times.

He agrees about your proposal that your common friend G. will ckeck the unit, so i send it back tomorrow morning. I opened no paypal dispute, preferring a quiet, courteous, friendly solution as i’m sure it’s not a big problem and i’ll enjoy that device when it is fully functional.

I don’t blame anyone. Things like that may happen without anyone being responsible.

He also mentioned that it had been very well packaged when sent from Japan, and though he’d not do a parcel as extraordinary as yours, i can confirm that the parcel was well done too and suffered no damage whatsoever.

Oh, and i forgot : thank you (both of you) for having mediated/made the issue much easier.

I have sent the parcel on April 27;

Hello People,

as promised, the seller’s friend checked my unit and posted this video :


it looks like there has been misunderstanding from the beginning and that the widespread mute zones are a normal behaviour from a dual SVF (?). Probably i have so little knowledge that i was not expressing clearly enough ? This is totally possible. As stated first, i’m quite new to all of this.

Please check the video. i can’t understand really what happened, how i could have been so wrong and stupid. Thank you.

what i fail to understand is that i was aware of course (by logical reasoning) that having 2 filters would let even less sound flow through, i can’t see where i flawed.

shall i F.O.A.D. ? ^^


i’m opening a new topic here as i got no answer in the following one :

i expected some feedback after the youtube video to confirm normal behaviour of my shruthi, from the people who told me there was very likely a hardware issue.

Weeks passed, and noone answered, and the Shruthi is back in my hands now, i still am being ignored, why ?


It may be that your question(s) are quite difficult to answer.

The dual svf filter is extremely versatile, and it’s definitely normal that certain configurations will result in no sound even when varying cutoff (e.g. a serial configuration with linked cutoff where the 1st hp filter the lower frequencies, and the 2nd lp then eliminates the remaining high frequencies). Also, there are of course certain cutoff settings that would eliminate all sound.

So to conclude it’s complicated, and I cannot tell from the video or your postings if the unit is ok. Maybe someone else is wiser.


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Aaah. Thank you Mister, for having bothered to reply. Your answer is cristal clear. Yes, it’s difficult, even more to me. I understand what you mean and suppose my shruthi is totally all right. I just found it hard to be suddenly confronted to deathlike silence from the whole community. I tried many settings yesternight and both filters react in some way to cutoff variations, so it’s very likely that none is dead.
Thanx again anyway. Have a nice day.

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Please don’t create new topics if you are unhappy with the response to the older one. If no one was able to help you in the older one, its unlikely posting new topics will improve the result, and we are low enough traffic here to make it annoying for other people.

In conclusion - don’t take it personally its one of the least common shruthi the amount of people who have the knowledge to help you are very small. I know I haven’t used one!

“If no one was able to help you in the older one, its unlikely posting new topics will improve the result”
It got me two reactions within a few hours when the former topic gave me an unpleasant impression of agreed boycott. Bjarne’s reaction is polite and comforting enough to me. I didn’t ask for more than that. Now please suppress my topics if you think i’m unmutual, i don’t care. I don’t mind about a society made of robots, clones of themselves. Brave new world.