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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
XOR chain + VCLFO = VC noise
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EATyourGuitar



Joined: Oct 28, 2010
Posts: 46
Location: Providence, RI

PostPosted: Sun Oct 14, 2012 7:45 am    Post subject: XOR chain + VCLFO = VC noise Reply with quote  Mark this post and the followings unread

I made two important discoveries with 16 square LFO's feeding a cascading XOR chain. the order of the inputs and the exact schematic of the XOR chain is not important since you can apply the communicative properties of multiplication -1*x=(-1)*x

as the title of this thread suggests, you can achieve voltage controlled noise. on an FFT you will see a resonant band that moves up or down in frequency as you increase or decrease CV to your LFO's. the LFO's can be any frequency as long as the frequency of the LFO's increases proportional to the LFO rate CV also increasing. while the resulting output of the XOR chain has no fixed frequency, it does have an average rate of zero crossings per second (the resonant band) that can be controlled by controlling the rate of the LFO's with a common CV signal.

the second discovery has less to do with VC noise and more to do with a noise sequencer capable of making complex repeating patterns using only 16 LFO's feeding into the XOR chain. VC over the LFO's is not required here but a sync input for each LFO is required. tune each LFO to an arbitrary frequency. sync 15 of your 16 LFO's to LFO 1. LFO 1 has nothing connected to the sync input so it will be the master clock acting as a reset for a sequencer who's length is infinite. there you have a 1 bit pattern that can be sync'd to any other gear. you could even clock it with more musical gear. optionally, you can insert clock dividers of /2 and /4 before any of the sync inputs to increase the length of the pattern while also decreasing the Q of the resonant frequency band.

I have not tried feeding a serial DAC but you could probably do it. with a serial clock divided by 8 running to your sync inputs on the LFO's. this would give you an arbitrary waveform generator that is driven from your serial clock or any other VCO in your system. you could generate upper and lower harmonics to your VCO without being stuck in square waves.
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trav



Joined: Sep 11, 2012
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PostPosted: Sun Oct 14, 2012 2:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

16 LFOs... I want to see your breadboard!
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EATyourGuitar



Joined: Oct 28, 2010
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Location: Providence, RI

PostPosted: Mon Oct 15, 2012 8:43 am    Post subject: Reply with quote  Mark this post and the followings unread

this is just math. you can do it on paper, on a breadboard, a modular synth, or on a computer. they all work. I'm using a software called VAZ modular. development of this sound was so much faster in software. I do have a modular and I do have a breadboard but I will save that for later.

http://soundcloud.com/robpaper/xor-noise-16lfo-test
I have included a sound clip and a screen capture of the VC noise patch. in the audio that I posted, it starts with two side by side 8LFO+XOR chains mixed in an audio mixer for 2 bit sound (16 LFO's). @ 0:43 I switched it to 1 bit sound with only 8 LFO's. @ 1:07 I switched it to 1 bit sound with the second bank of 8 LFO's. the LFO rates are tuned differently on the second bank so you may notice a difference from 0:43 and 1:07.


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trav



Joined: Sep 11, 2012
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PostPosted: Mon Oct 15, 2012 2:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ah, that makes more sense. I get the math; for some reason I thought you'd made the discovery in the course of some ambitious breadboarding and worked out the theory afterward. It's a great result! like waves crashing on a beach. Now I really do want to see a hardware implementation.
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analog_backlash



Joined: Sep 04, 2012
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PostPosted: Wed Oct 17, 2012 4:56 am    Post subject: Reply with quote  Mark this post and the followings unread

Just a word of caution

The VAZ modular software that you're using looked very interesting, so I searched for it and found the web site vaz-synths(dot)com. However, my Norton Antivirus flagged it up as an unsafe web site with 2 threats, so I didn't delve any further. It's a shame, because I would like to see more about it.

Gary
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Blue Hell
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Joined: Apr 03, 2004
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Location: The Netherlands, Enschede
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PostPosted: Wed Oct 17, 2012 8:27 am    Post subject: Reply with quote  Mark this post and the followings unread

The support forum for VAZ is http://www.kvraudio.com/forum/viewforum.php?f=147 so maybe have a look there? It probably is a false alarm ...
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analog_backlash



Joined: Sep 04, 2012
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Location: Aldershot, UK
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PostPosted: Wed Oct 17, 2012 3:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for that link Jan. I notice that one of the topics listed on that site is about false positives for malware/viruses etc. from antivirus software, including Norton. This probably explains my problem.

Gary
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