Frequency Modulator

[rictusergic]

Kinda new to the DIY thing and circuits, so this might not be at all what I imagine---but, been considering FM as in the DX7 synth---is there a circuit that uses the frequency of one sound source to modulate another?  I know of the ring modulator, which I read is an AM device---if I understand this right, one has a steady amplitude and a changing frequency, the other vice versa, so I could imagine that both might sound the same---but maybe not?

[Mark Hammer]

Nothing really as "pure" as the FM found in the synth world, really.  Remember that guitar signals (which is 95% of the stompbox universe) are fairly complex, both in terms of their amplitude envelope, and their spectral content.  Of course, part of what something like FM in the DX7 context attempts to do is model what happens when a simple source is energized.  If I pluck a string and impart some energy to it, both the amplitude of the string's movement, and the compliance of the string as that energy dissipates (more energy is needed to make that string really "bendy" and produce harmonics), represent changing energy over time.  That is, in effect, what FM tries to emulate.

[Strategy]

You can get into some interesting territory with LFOs that go so 'fast' that they go into audio rate oscillation. The Gristleizer project in this forum has an LFO that gets up in the bubbly sounding audio range modulations and that is sort of like frequency modulation. In that case though, it's not the guitar input frequency that's being modulated, it's either the pedal's VCF or VCA. But once that LFO gets up into the audio range it's pretty weird and FM-like. One pedal that is dedicated to this sort of trickery (not a DIY project) is the Moog FreqBox.

Nothing really as "pure" as the FM found in the synth world, really.  Remember that guitar signals (which is 95% of the stompbox universe) are fairly complex, both in terms of their amplitude envelope, and their spectral content.  Of course, part of what something like FM in the DX7 context attempts to do is model what happens when a simple source is energized.  If I pluck a string and impart some energy to it, both the amplitude of the string's movement, and the compliance of the string as that energy dissipates (more energy is needed to make that string really "bendy" and produce harmonics), represent changing energy over time.  That is, in effect, what FM tries to emulate.

[soggybag]

Here's a link to a post on my site with an image of a Frequency Modulator.

http://www.super-freq.com/2010/03/fm-modulator/



This design comes from the infamous Stompbox Cookbook. I tried to breadboard this once and couldn't get it to work.

Seems guitar controls the 555 timer via pin 5 the Voltage Control pin of the chip. The 555 is set up as an astable oscillator with a high frequency, beyond hearing. The second chip is here I get lost. This is some type of PLL. I'm assuming the 567 demodulates the signal from the 555 to extract the original signal with some interesting artifacts.

Part of the drawing is missing. I can post this if anyone is interested. If I recall there was nothing put a maybe a cap and volume control. I had hit the edge of the page in my notebook.

[rictusergic]

So you never got it to work, huh was mainly wondering it this was potentially interesting new sonic territory or if it sounds much like something else.

[rictusergic]

Oh, I forgot to mention this part *2 inputs* I mean to have control of both inputs, like modulating one guitar with another, or maybe modulating my guitar tone with the output of a radio, or whatever---- not an internal oscillator. That Moog Freqbox is hot, but yeah, that wasn't exactly what I had in mind.

[Taylor]

Ring modulation really is what you want for modulating a guitar with another guitar, etc. It's technically not FM, but in point of fact, the DX7 is not FM either, it's phase modulation.

I have actually experimented in the digital realm with a pitch shifter whose shift amount was controlled by an audio signal - true FM. It was not a particularly interesting sound, and I'm a ring mod fiend.

The closest you'll get to an FM synth with guitar is to take a pitch-tracking sine wave (very tough to make that) and use it as the carrier in a ring modulator.

If you don't want an internal oscillator, and you only want to modulate 2 sources against each other, the classic passive diode ring modulator is perfect:

http://www.asciipr0n.com/4096/ringmod/index.html

I recommend using a UC3611 quad diode array for the diodes, since they are perfectly matched. This makes the sound less gated. However, if you want to sound even remotely like an FM synth, I think you'll find that modulating a complex signal - like a guitar - with another complex signal - like another guitar or radio - doesn't sound remotely like FM synthesis. It just sounds like distorted racket. (But maybe that's what you're after)

[soggybag]

Nope, I couldn't get it to work. Which is not saying much, since there are a few projects I haven't been able to make work. This is also taken from sort of an idea presented in the book rather than full fledged project.

I didn't give this too much effort. I put the whole thing on the breadboard and nothing happened. I poked around for bit with the multimeter and the scope and gave up.

There is another project from the same book with a similar concept. Here the signal is modulated in the same method using a 555 clocked at ultra sonic frequency. Then the signal is sent out through an ultra sonic transducer. The device has an ultra sonic receiver that picks up the signal and demodulates. The demodulator in this case is a high pass filter.

http://www.super-freq.com/2010/10/distort-o-matic-vi-2/

I etched a circuit board for this and then realized the PCB layout is a positive. I've been sitting on it for some months. I figure I bend the legs of the three chips over backwards and use them. Now that it's come up again maybe I'll give it a try some time soon.

[jasperoosthoek]

I own a 600kHz frequency generator with an amplitude modulation input. It's probably from the early 60s. The frequency can go down all the way to DC. The generator by itself sounds like a manual theremin (knobs instead of antennae).

I connected my guitar some years ago to the modulation input and set the internal frequency to some tuned note in the audio range. As expected you get two new tones of the sum and difference of the two frequencies, just like a ring modulator. The difference note is very weird cause it goes down if you bend a note up...

If you like sonic weirdness then that's your thing .

[Rectangular]

its possible to do synthesizer style  frequency modulation to a guitar signal.  if you modify a chorus or delay unit's LFO to oscillate at a higher rate (something in the audio range) , then its functioning as a frequency modulator, and it sounds like it should. I guess this was never popular in the guitar pedal world because like similar effects (ring mod), its not subtle, so you can't really play "music" with it. its great for us electronic musicians though