A pedal that uses AM/FM radio waves to alter its effect, possible?

[Mullers]

Hi there,

To cut to the chase, I had a random idea for a university assignment of creating an effects pedal that uses AM/FM radio waves to alter its effect, creating a sort of live effect that couldn't be recreated. Unfortunately, having dropped my electronics hobby years ago, i'm a noob again and don't know how to go about and am  not even sure if it's possible.

In the case where a reader would be unsure here is a sort of example: A wah-wah pedal with essentially a tunable radio on board which would somehow affect the wah (you can tell by this point I have little-no idea what I'm talking about).

So yes, if one of you cool dudes out there could tell me if/how this is viable/impossible that would be fantastic!

Sorry for being potentially very naive and cheers,
Mullers 

[darron]

i like the idea. let the universe provide something to work with your music.


so what you want to do use use an unpredictable wave shape to alter your guitar sound. first thought to me, this sounds like when you use any kind of LFO in modulation. that does the same thing.

you could modulate attenuation like a tremolo
phase inversion corner frequencies like a phaser
delay time like a vibrator / chorus
wah / envelope-style trigger.



but whatever the effect you use, i guess you'll hear the radio in some way. so if some guy comes on trying to sell vacuum cleaners in some way that's what you'll get.

maybe you could tune it in to an electro station an just use the lower registers for some type of modulation? but then you'll have to pay them right for use of their beat of course...

[Mullers]

Cheers for the sharp reply,

Basically hit the nail on the head, mate. I want to make something that the environment can interfere with.

Now all I'm stuck for is how to make it electronically.

How do I get the radio signals to affect a circuit like this?

[FUZZZZzzzz]

very cool idea! reminds me of a couple of things... but your idea is way more interactive

http://www.mysterycircuits.com/radioace/radioace.html

[Mullers]

Hmm, I hadn't considered a drum machine - I like it! As the static creates a sort of snare. Very cool.

4th video is somewhat similar to what I had imagined. Though would it be possible to have the effect only sounding on the guitar and not a constant?

[blackieNYC]

If we can get rid of a ticking square wave, we should be able to get rid of any modulator - but - your modulator idea is either in the audio range (radio program material) or beyond (carrier frequency). You could avoid using it as a direct LFO, and maybe filter the hell out of it.  Imagine a talk show with a steep lowpass. The pledge of allegiance takes ten seconds for fifty-some syllables. That's 5 cycles per second on average, but completely inconsistent. Varying with the rhythm of speech. That seems like a great tremolo.
The RF thing reduced to a LFO friendly frequency. Hmm. Makes me think of a neon beer light and a single coil. I think a slow modulation could be obtained by the variations of a signal strength meter. A single coil used to control a VCA?  That would change in relation to the single coil's orientation with regard to the Bud sign. This single coil has to move. Tape it to your guitar neck.  (There already is an accelerometer pedal like this). Tape to your drummer's elbow. The RF doesn't change all that much to do this though. The single coil pickup would have to go in and out of the building, or be driven around some hills. Hmm. Gotta be a way.  Very directional antenna. Signal strength measurement.

[marmora]

This isn't the most guitar-friendly design, but it does work on guitar (I built one many years ago and eventually sold it... )
I like your ideas, maybe this will get you closer

http://www.gearbug.com/product_info/the_squarewave_parade_the_mingrod

http://electro-music.com/forum/topic-16354.html

[Ben Lyman]

How about this:
The guitar input jack of the pedal goes to an AM transmitter.
Also within the pedal is an AM receiver that goes to the amplifier output jack.
The tuning knob is on top and only turns enough in each direction to just lose reception, middle is as perfect as it could sound.
Now, take that tuning knob and make it be the pot inside a Wah/volume type enclosure.
Follow me?

[digi2t]

How about using a sample/hold type circuit to inject the radio signal into the audio? I think that's as random as it gets, no?

Then stick the works into a wah, and use the treadle to fade between audio, and audio/radio mix.

Now that.... would be sick!

[Mullers]

Some great ideas here guys, gonna give them a good think and look over in the morning (Brit here)!

And many thanks for those schematics and such marmora, I'd love to hear more about your build!

[samhay]

If you don't actually want to hear the radio station, but simply want the universe to play some nebulous role, you could use the radio signal to generate an envelope that then controls something - tremolo, pitch shift, level or whatever else you fancy using envelope control for.

[Kipper4]

Well you couldn't write it.

http://www.diystompboxes.com/smfforum/index.php?topic=112737.0

[R.G.]

As an even simpler approach, along the lines suggested by Darron, is to just use a random-enough signal of some kind.

Something I worked on was a pseudorandom signal generator with a long repeat time. It turns out a signal that is repetitive, but between repeats is indistinguishable from white noise. This can be done with microcontrollers, and I did one that - if I did the calculations right - will have a repeat time in the thousands of years, so in between it's random. This can be low pass filtered for lower frequency content, more of a random wobble than raw hiss, and could be used for your suggestion. I think I posted about it here.

Once you pick your random signal, you feed it to ...something... that modifies your pedal effect. Suitable things include LED/LDRs and JFETs set up as variable resistors, etc.; the usual suspects for modulation of some kind.

It does not use radio as a source of random-icity, but I think it might be along the lines you're thinking.

[Mullers]

Ultimately does anyone have an idea what the schematic would look like or links to similar ones? Like I say, It's been so long that I'm a complete amateur at circuits these days.

<3 <3 

[Transmogrifox]

I have had 2 ideas percolating in the back of my mind for some years:
A)  Heterodyne modulation effect.  If you take an audio band signal and AM modulate it onto an RF carrier, you can place it back where you left it by multiplying the resulting signal with the carrier again and filter off the high frequency stuff.
If you frequency modulate the carrier (or the IF signal) the result will be a pitch shifted version of what is in the audio band.  It will be somewhat like a chorus except instead of everything remaining harmonically related, it all shifts up and down linearly.  This is what is implemented in single side-band effects (Hilbert transform).   My thought is it could be more simplified by not implementing SSB, but keeping the deviations slight so that it generates a subtle modulation effect with cross-multiplication terms simultaneously shifting up and down ( the "negative" frequency bit will be moving down in frequency as the positive frequency part is moving up).

B)  "S-curve" distortion.  You can frequency modulate a signal using a relatively wide modulation depth -- maybe 60 MHz carrier pushed to 1 MHz bandwidth.  Then you multiply with an IF of say 500 kHz and run it through a high-pass filter in which the IF is set at -12 dB on the curve.  As the frequency increases, the output amplitude from the filter increases -- but only to the pass band.  That way the magnitude vs frequency looks like a nonlinear limiting curve.  Might create an interesting soft compression/clipping effect.  Then you just rectify and filter the RF so that you recover the audio band stuff -- slightly compressed/distorted.

C)  You could make a dynamic range compressor built on the same principle.  Because an analog filter naturally follows a logarithmic curve you can use the envelope detector to drive a voltage controlled RF oscillator and then process the oscillator output with an RC filter, then rectify and filter to get the logarithmic function typical of compressor gain control.  If you modulate the audio signal onto the carrier using something simple like AM, then the VCO pushes the overall amplitude up and down the filter response curve.  What you will recover is a logarithmically amplitude-scaled version of the original audio.  Basically an RF VCA.

More complicated than it needs to be to make any of those effects but fun and educational from the experimenter point of view.

[Mullers]

They are some fantastic ideas!

[Mullers]

Would it be possible to build something similar to this with a radio built in?

http://www.gearbug.com/product_info/the_squarewave_parade_the_mingrod

[Mullers]

Additionally, another noob question, where could i buy the components and board for this build?

Cheers