PITCH OUT to FILTER IN: Is it safe?

[Quinthius]

Hi all,

I don't have any other analog/modular synth components, but curious to experiment with the CV/gate stuff (and thus the addiction will begin...)  I was looking at the back and wondering... would it be safe to route the PITCH OUT over to the FILTER IN.... ?  I'm assuming routing back into PITCH would probably be a bad idea (I'm guessing this might create some kind of endless feedback as the pitch tries to modulate itself, or would it stop at just one iteration?  If this would be safe I would actually love to try it too).  To my novice mind, Filter seems like a somewhat safe thing to try try.  Am I totally mistaken here, or would it create some kind of Filter FM effect based on what notes I play?

I'm afraid to do it without some more knowledgeable input as I don't want to damage anything.

And I guess, since I'm too chicken to try it just yet.... would this even produce anything usable in the first place, or not worth doing?

Thanks much for any input!

[yusynth]

It cannot harm your MiniBrute but it is completely useless since the cut-off control of the filter is already driven by the pitch CV through the Kbd Tracking potentiometer

[beefinator]

AFAIK, you can't damage anything.

But you definitely won't get anything interesting.

The pitch out is not an audio signal output.  It is a CV signal.  It has nothing to do with the waveforms, it is just a voltage that represents the pitch playing.  I forget the exact mapping, but an octave up in pitch is a CV output of 1volt higher.

So, routing it to Pitch CV in would do nothing, since it's just routing a signal back to where it came from (it mixes the pitch CV with the voltage that comes from the keyboard; if both are the same, the mixed voltage is the same)
Routing it to Filter CV would vary the cutoff of the filter based on the note.  I think the filter CV input is also approximately 1v/octave, but obviously the filter cutoff being stable in tune isn't critical like an oscillator.
So, you'd just get a less flexible version of the Keyboard Tracking knob, which does the exact same thing, except you can change the range from 0% to 200% (filter cutoff goes up 2 octaves when the pitch goes up 1)   

[Quinthius]

So I went ahead and tried this anyway and it didn't do what I thought it would... guess I was thinking "oscillator out", like the pitch out would actually output an oscillating signal.  See how much of a newbie I am?   I think I understand better now... it doesn't actually output an oscillating signal, just a set voltage for pitch tracking.

So in effect patching pitch out to filter in, just creates a kind of filter tracking.

[Quinthius]

Thanks for the helpful responses!  I completely understand now.

[yusynth]

Yes you got it right now

[stevism]

what if he wanted to use the headphone jack or main out for this purpose? is it possible by any means?

[yusynth]

If you mean feeding back the headphones output in the filter CV IN, there is no problem at doing so, you will obtain strange feedback modulation probably.

[stevism]

that is what i meant...awesome! i think that's what OP wants to try

[Quinthius]

I went ahead and tried the headphones -> Filter CV IN, played around with that for a while... could notice some differences but nothing greatly interesting.

Then I tried headphones -> Pitch CV IN.  Much more interesting results from that... weird out of tune pitch changes and stuff, "cat" whining type of sounds, etc.  Got a little carried away in that mode, trying it with Brute Factor, etc.  Got some pretty extreme sounds doing this.

Now I am concerned - is there any way I could have damaged the unit by going from HEADPHONES to FILTER CV IN or PITCH CV IN?

Now after I go back to "normal" I feel like I'm hearing a fuzz/buzz noise from the filter that I did not notice before, even on a sine wave sub osc.  I can hear it through the head phones and through the audio out to my audio interface and monitor speakers.

What's weird is I can filter out the "buzziness" with the filter cutoff... I know I swear I did not notice it there before doing all this.

Could the oscillator or filter have been damaged by high input from the headphones output?  Is it even possible?

[beefinator]

aw man that's amazing... why didn't I think of it?

you even have a modulation depth knob! (headphone volume)

I'm going to have to try this.

[Quinthius]

I made a sound clip... Can someone listen and tell me if the sine wave sub osc is supposed to sound this buzzy?  Maybe I just did not notice it before.  The triangle and the other shapes seem to have this extra buzziness too, but of course it's hard to "hear" it more clearly on them.

https://soundcloud.com/quinthius/sinewave-test

Everything is turned "off" or at neutral positions, filter completely open, no resonance, no brute factor, etc. Just a little bit of VCA release to hold the notes out longer.  Made sure nothing was clipping during recording.  This is what I hear through headphones also.

If it is supposed to sound cleaner than this, I think I might have damaged something

[yusynth]

There is no reason why this should have damaged something because the voltage levels at the output of the headphone output is way within the acceptance range of the CV inputs.

[Quinthius]

Great - thank you so much, that eases my mind a lot.  I really appreciate your comments!

I think I didn't notice this specific "buzz" sound before, but it must have always been there.  Now I can't get it out of my head, I am hearing it on all the oscillators!!!

I found some videos of Doepfer modulars demonstrating raw Sine and Triangle waves, and I hear a very similar, very audible "buzz" even on the sine wave so it must just be how the analog/modular world of oscillators sounds.  I listened to the oscillators on my MicroKorg (digital synth) in direct comparison and they were very much cleaner, so that had me even more worried - I could not tell if what my MiniBrute was making was normal analog oscillator sound or if something really was "distorting" somewhere.

I guess I thought a sine wave should be perfectly clean and triangle should be much more mellow, but this appears not to always be the case.

So I will just accept this as normal unless someone thinks my sound clip does NOT sound right.

Thanks again!!!

[yusynth]

OK I checked on one of my two MiniBrutes (Yes I know I am a bit greedy son of a bitch  ) and I have the same kind of buzz on the sub-octave sine. It 's only because the sub-osc is rarely used on its own that usually this buzz cannot be noticed. This buzz is "somehow normal" because it is not a perfect sine wave that is produced, it is obtained by a complex reconstruction based on the sawtooth and any slight linearity defects of the slope of the sawtooth has an impact on the building of the sine wave : therefore a slight asymmetry of the reconstructed wave creates odd harmonics which are responsible for this buzz. For a pure sine it is necessary to filter out these harmonics withe low pass filter.
You will notice that on most VCOs (in modular) where the sinewave is built the same way, there is always some harmonic distortion that creates this slight buzz.