# Frequency doubling (was The only stupid questions)

This maybe a stupid question, BUUUUT if I mix a signal (gate/trigger) with it’s inverted output will it double the frequency or cancel it out?

In a perfect world they would cancel out.
But in the world we live in, the edges always have some slope (they don’t change instantly from “off” to “on”), so you’ll get (very short, too short for almost all synth purpose) spikes at double the frequency.

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Thanks! I was too curious to wait to get home and try it. Until I get home…I may still try it.

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There are ways to double the frequency of a clock or other periodic signal… but this isn’t really one of them.

Rectification and AC coupling turns a triangle wave into a double frequency triangle wave, but doesn’t work with square/pulse waves (e.g. clock signals).

A clock signal can be doubled using a CD4046 phase locked loop chip and a flip flop or binary counter chip.

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You wouldn’t happen to have a schematic for that 4046 circuit, would you? I have a 4024. Would that work for the binary counter? I may have all the supplies…

Another possibility, good for 1Hz to 1Khz:

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Not really — the Barton Wave Shaper sort of contains the gist of it: It takes an input signal, converts it to a square wave, and then produces pulse waves at 8x, 4x, 2x, 1/2, 1/4, 1/8 frequencies and combines them along with the original square wave. So the core of a clock doubler/divider would be there, with pulse waves going to separate outputs, but it’d need a clock conditioning input instead of the wave->square converter. It’s also set up for audio frequency instead of low frequency. Note it wouldn’t work instantly, it’d need enough pulses to lock in on the octuple frequency. Or double frequency (which presumably wouldn’t take as long) if you adapted it to just do doubling and not quadrupling/octupling.

There’s also this, though designed for ~ 1 MHz digital clocks:

That’d work, looks like, though only for square (50% duty cycle) clock pulse inputs and producing << 50% duty cycle output.

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I think I’ve seen the Barton schematic…I’ve NEVER been able to get a Barton circuit to work on breadboard (or any other “board” for that matter since a working breadboard is what I require to move on to any permanent circuit). Your circuits have more stock in my faith department.

Hmm, funny, I have a Barton circuit working on a breadboard right now. (And I’ve built the Wave Shaper and it works.)

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That is HILARIOUS! I love this place. You guys rock. I swear I’m not trashing Barton. I really wanna buy one so I can say I have one. It has to be a cosmic coincidence. SOMETHING goes wrong ever time I try Barton. That “something” only remains undetermined by another seemingly coincidental fact that I have always had an alternate circuit either built or plans on deck to try. In either case I never put much effort into solving the problem by reason of not needing to. In the case of the Barton Analog Drum I got a suggestion from you which prompted me to build Thomas Henry Bass++ which, coincidentally, worked (my first Thomas Henry). I actually got the suggestion for both circuits from the same thread on this forum. Coincidence… Perhaps not

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I will add that rectification and AC coupling (as suggested by @analogoutput ) is also the way with which many classic “octave” and “octave/fuzz” guitar effects get their octave up. Obviously, the input signal from a guitar is not a sine/triangle, but it’s more dissimilar to a square so these effects kinda work and you get a sense of an octave up, although you need a lot of imagination! Also, that explains why these effects won’t work if you put any other distorted effect before them (because it will most likely square off the guitar signal).

For the CD4046 approach suggested by @analogoutput you need to insert the counter/flip-flop between the VCO output and the comparator input (datasheet, p. 19). You can then use the rest of the counter outputs to divide the multiplied signal, and combine those divisions into all sorts of weird harmonies. This is also how all these weird PLL guitar effects work.

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Somehow I missed all the interesting replies while I was typing my response (and multitasking with work emails as usual)!

Re: Barton circuits: I haven’t tried any, but I have a few on my to do list. What I noticed is that he uses a kind of mangled way to present the connections in the schematics. The lines go in all directions with sharp corners etc. While the end result is electrically correct, it can be a challenge for people who are used to a more linear/tidy presentation of schematics.

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For rectification to really work you need a waveform that has an appropriate symmetry*.

For a triangle it works perfectly:

For a sine wave you get a double frequency result, but it isn’t a sine wave:

For a ramp wave you get a triangle wave of the same frequency:

For a randomish squiggle you get a different randomish squiggle of the same frequency:

And for a square wave you get nothing at all:

* The second half of the period must be the same as the first, but inverted.

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Yeah, I kinda like the schematics. They look cool. I’m gonna build one, successfully, eventually…

I’m gonna research this method for a simple schematic. I’m super curious. I’ve been wanting to do some guitar effects projects.

Looking at it again it seems it would be difficult to mess up. Too simple. It’s definitely worth a shot I just need to get some 4040s.

Well, I was simplifying the guitar analogy. The guitar signal in octave effects is not treated as some radom waveform, but is converted into two out of phase signals which are then rectified and added. Or something like that

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Maybe one of these…

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Heres a few more to consider:

The first 2 are 4046 PLL based, I had more like this but cant find them

More conventional octaver-fuzz circuits:

Ive tried a few versions of the green ringer and was impressed, I even made my own derivative called the black ringer which used opamps instead of transistors

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Wow thanks! I really want to make a guitar pedal with a few effects. An octaver would be so cool! With fuzz and a filter…

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