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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
XOR mixing
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astroman



Joined: Sep 13, 2012
Posts: 44
Location: UK

PostPosted: Sat Jul 06, 2013 12:05 pm    Post subject: XOR mixing Reply with quote  Mark this post and the followings unread

Really on a roll with my yellow box Lunetta this weekend!
Chanced upon a thing today where I feed an oscillator into pin 1 and the output of a melody generator into pin of a 4070. There was a pot between pins 2 and 3 and the signal to my mixer came out of pin 3. Sounds great! What exactly is happening here?
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analog_backlash



Joined: Sep 04, 2012
Posts: 391
Location: Aldershot, UK
Audio files: 21

PostPosted: Sun Jul 07, 2013 4:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi astroman.

It sounds like you're getting the pseudo ring modulator effects - see:

http://electro-music.com/forum/viewtopic.php?highlight=4011+ring&t=48145

Here, 4 NAND gates are used, but as is pointed out here, this arrangement of NAND gates gives the same output as a single 4070 (or 4030) XOR gate. I'm not quite sure about the pot between pins 2 and 3. I suppose your feeding the output back into an input, which I haven't tried doing (but it sounds like an interesting idea).

In a true ring modulator, if you feed in two different frequency signals, the output consists of a mix of the sum and the difference of the two frequencies (e.g. 500Hz and 2kHz would give outputs of 2.5kHz and 1.5kHz). These can be mixed with the original inputs, to give a complex sound, which is often like bells, gongs and various metallic objects being hit (especially when you add reverb). The XOR gate produces very similar effects to this, but it's limitation is that it needs square waves to work (it is a logic chip after all). True ring modulators can work with any audio signal inputs.

Gary
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JingleJoe



Joined: Nov 10, 2011
Posts: 878
Location: Lancashire, England
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PostPosted: Mon Jul 15, 2013 12:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

analog_backlash wrote:

It sounds like you're getting the pseudo ring modulator effects

Acctually XOR is real 100% ring modulation, the effect is exactly the same, but only for digital/square waves.

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analog_backlash



Joined: Sep 04, 2012
Posts: 391
Location: Aldershot, UK
Audio files: 21

PostPosted: Mon Jul 15, 2013 3:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

JingleJoe wrote:
analog_backlash wrote:

It sounds like you're getting the pseudo ring modulator effects

Acctually XOR is real 100% ring modulation, the effect is exactly the same, but only for digital/square waves.


Yes, you're dead right JingleJoe. I didn't explain it very well - the "pseudo" was there only because this circuit is limited to square waves. I suppose that you could feed it with any signal that you have "squared up" first e.g. with Tim Escobedo's PWM circuit, or just a hard-driven transistor - I also imagine that this has already been done by somebody Smile .

Gary
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