SV Filter PRC3A as oscillator - from sine to chaos

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otoskope
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SV Filter PRC3A as oscillator - from sine to chaos

Post by otoskope » Sat Jan 28, 2012 11:10 am

We're all hailing the bug SV Filter as a great module - to be pinged for nice percussion, as a smooth multimode filter, etc. Sometimes people complain that it is not self-oscillating. I did a little investigation of how to make it generate various waveforms, and I was surprised. It can generate a vast variety of waveforms, all by itself, with just a couple of feedback chords.

A few general comments:
* All waves are generated by a single SV Filter module going directly to output/oscilloscope (green banana).
* The photo to the right shows the exact settings rendering the wave to the left.
* The oscilloscope parameters were adjusted to show the wave clearly. Real amplitudes vary, as do the frequencies depicted.
* All these waveforms work over the full audible range, and can be controlled with the 1V/oct input, which was not used for feedback. EDIT: And quite a few of them seem to work well down into LFO range, with the help of negative CV. Some I have gotten down to the 15sec range. That may change the waveform a little bit, though.
* Altering the modulation amounts (Fmod, Qmod) and Q often changes both waveshape and frequency, which could be considered good or bad, depending...
* Running the feedback signals through VCAs would allow some serious waveshape morphing.
* I made no sound examples, as most of you have this module. The pictures show clearly that this is a wavegenerating treasure-trove! Start exploring!

First, some basic waveforms:

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One way to make a decent sine.

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Another quite pure sine.

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A triangle wave, also almost perfect.

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Rising saw. I needed some FM to achieve the saws.

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Falling saw. This one just flipped two cables compared to the previous one.

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Sort of squarish. Certainly sounds like one.
EDIT: This was actually a pretty good square, until it was plugged into the output mixer module, which somehow distorted the negative part a little.

Over to some stranger waves:

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A folded sine. No FM used!

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A weird one.

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The previous one, but with FM added, and some more Q. Makes the peaks sharper.

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Adding Q modulation gives interesting hi-freq pulses on the waves. Not unrelated to Metasonix weird pulser circuits.

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Some more intense pulsing.

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This one is unstable, altering between the two depicted shapes. Interesting.

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Some hard FM to create sharp peaks.

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More FM. The very sharp impulse on this one contains very high partials.

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A very simple one, with weak fundamental, nasal sound.
EDIT: Just realized this is actually a softer, slightly rounder version of the folded sine above - with slightly lower Q.


Finally, a few saw-pulse combinations:

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Notice that this one alters between two and three saws on each wave.

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[EDIT] Added some quadrature and dual waveforms:
(red and green banana)
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Quadrature sine, i.e., two sines 90 egrees apart. They don't have equal amplitude when output from the module (adjusted in the oscilloscope), but still...it you're happy with a not-so-pure sine, you can increaase the Q and get less difference in amplitude.

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Square and triangle, with quadrature phase difference.

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Sine-ish wave and square, 180 degrees out of phase.

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Saw and U-wave, in phase.
Last edited by otoskope on Mon Jan 30, 2012 4:23 am, edited 3 times in total.
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tIB
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Post by tIB » Sat Jan 28, 2012 11:16 am

Oh my! :omg: :omg: :omg: :omg: :omg: :hyper: :hyper: :hyper: :hyper: :hyper:

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Post by radams » Sat Jan 28, 2012 11:23 am

thanks for being here Palle - your extra brain power makes up for the part of mine that has rotted out !
Seriously - your knowledge is a great resource and I appreciate your willingness to explore and share

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Post by otoskope » Sat Jan 28, 2012 11:26 am

I'm not sure about the extra brain power. But I have no lack of curiosity!
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Post by otoskope » Sat Jan 28, 2012 12:19 pm

Added some quadrature and dual wave configurations to the end of the post!
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Post by jenamu6 » Sat Jan 28, 2012 12:29 pm

Wow :bacon: :yay: :nana:

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Post by darenager » Sat Jan 28, 2012 2:12 pm

Yeah go Palle!

The SV filter is astonishingly good, and flexible - I have 7 now! And really could do with some more.

Feeding back as you have shown here is a great way of unlocking some really great stuff, stick a VCA between the output being fed back and you have VC feedback. I have not used mine as oscillators aside from being swept for drum stuff, but I have used feedback to change the response of the filter on the Bugphonic stuff with really great results.

Thanks for posting this!

:tu:

EDIT - I must admit that I actually prefer that it does not really self oscillate, as I find that the trade off is that when being used as a filter it is much more stable and easy to control, and having owned a lot of filters I think I can easily say the PRC3a is easily by far my favourite.
Last edited by darenager on Sat Jan 28, 2012 2:16 pm, edited 1 time in total.

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tIB
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Post by tIB » Sat Jan 28, 2012 2:14 pm

^ I want 7!

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Post by darenager » Sat Jan 28, 2012 2:17 pm

No Mr Tibbs, you NEED 7 :lol:

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Post by otoskope » Sat Jan 28, 2012 2:18 pm

I only have 4...poor me. I also need 7, at least!
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Post by miditerranean » Sat Jan 28, 2012 2:27 pm

Very impressive, otoskope! Thanks a lot!

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Post by tIB » Sat Jan 28, 2012 3:17 pm

I reckon I need 5... currently keeping my eye out for a thrid. [/i]

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Post by indexofmetals » Sat Jan 28, 2012 3:23 pm

:hail: :hail: :hail: Palle

time to unpack that Parcel from Tom and get out the extra SVF

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Post by a100user » Sat Jan 28, 2012 4:00 pm

Way to go Palle

I'm off to play :tu:
I'm looking for nothing at this moment in time

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Post by indexofmetals » Sat Jan 28, 2012 6:38 pm

besides more svf (I now have 3) I need an oscilloscope (not sure if I can eve spell it). what would anyone recommend?

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Post by otoskope » Mon Jan 30, 2012 4:25 am

Added some comments to the waves above, especially one about having modulated some of these waves down well into CV range, down to maybe 15 sec per cycle when I was using a negative CV offset into the V/Oct mod in.

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Post by oljud » Mon Jan 30, 2012 10:20 am

I for one wouldn't mind a super-sfv with all four outputs available at the same time... And extra tasty goodness of course. CV over fm amount, pre gain knob, mix output..?

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Post by BugBrand » Mon Jan 30, 2012 10:32 am

Sterling work from Palle!

Mega-SVF -- the thought has crossed my mind before, that's for sure..

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Post by otoskope » Mon Jan 30, 2012 12:13 pm

oljud wrote:I for one wouldn't mind a super-sfv with all four outputs available at the same time... And extra tasty goodness of course. CV over fm amount, pre gain knob, mix output..?
I did think the same thought today, while reading up on the Serge Variable Q Filter, which is very similar, I think, and has a few of those features. But on the other hand - CV control of FM (add a VCA), pre-gain (add a pre-amp), mix output (add a dual DC mixer) are easily available already. Just add another module. I can't really see the point of those features being built in.

But all four outputs at the same time: YES! :nana: That would make a big difference. And a switch for hi/low range. You can certainly push this into CV territory.

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Post by oljud » Mon Jan 30, 2012 12:18 pm

Yes, I know, I just figured that 2 more outs would push it into 2fw territory anyway so one might as well put in something extra.

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Post by tragedybysyntax » Mon Jan 30, 2012 12:29 pm

Holy crap... can we hear samples? ;)

SV Filter has to be the BOMB! Eventually I'll snag one.... or 3!
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Post by otoskope » Mon Jan 30, 2012 12:32 pm

Didn't we just agree that 7 was the recommended dose?
EDIT: No, sorry, I didn't make any samples. That would've been too much work. Took almost a full day to make that series of examples anyway, and when the post was almost ready, my computer went zen... But you'll have one, soon! Then 7...

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Post by otoskope » Mon Jan 30, 2012 6:02 pm

tragedybysyntax wrote:Holy crap... can we hear samples? ;)
Yes, now! I just uploaded a sound/video example in a separate thread: viewtopic.php?t=51704

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Post by KNYST » Tue Jan 31, 2012 5:05 pm

Hmm... I messed around with feedback quite a lot when I got my first PRC3A, but didn't find much use for it, part from when running an audio signal through it simultaneously, but I guess I was lazy :tu:
Never thought about looking for quadrature sines, despite using my Serge equivalent for exactly that :doh:
Very kind of you to post all those scope grabs and patches!
Tackar.

And this:
maybe 15 sec per cycle when I was using a negative CV offset into the V/Oct mod in.
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