Ring mod with adjustable frequency - suggestions?

[swamphorn]

... if it's followed by a filter (as would be typical on a synth) then that's not necessarily a problem.

On that note, I've had this idea for a "smooth but cheap" ring modulator that wraps a square wave / switched-inversion / analog-XOR type ring modulator with pre- and post-filtering; either a pre-/de-emphasis scheme (differentiate -> chop -> integrate is equivalent to ring modulation with a triangle wave), or perhaps matched band-pass filters on the input and output so as to modulate a more restricted band of signal (I would expect this to be more amenable to dry-blending).

Or, you could go the other way; fuzz up the guitar signal and use the squared up signal to chop a low-harmonic carrier waveform (and either the carrier or output would need to be gated by transitions of the fuzzed-up signal, as it never itself goes to zero).

[Knobby]

A ring mod with both inputs the same remains one of the methods of getting an octave up, since the sum of two identical frequencies is a DC level plus an output of twice the input frequency.  Most people use fullwave rectifiers but this generates a lot of harmonics.  A linear multiplier would not necessarily have an output quite as rich in harmonics.

What's the disadvantage of using a ring mod like that to generate an octave? I assume there must be one, otherwise we'd all be doing it to get a cleaner octave up than a standard octave fuzz.

[Mark Hammer]

I suspect the answer to that question is to be found in the quirks of the guitar signal itself.

Many years ago (1970, IIRC), I was studying for an exam in the lounge of a student residence.  I was lying on a sofa, leaning back, and ultimately upside down, holding the textbook in front of me.  When I put the book aside for a moment, I was gazing out at all the folks exiting and entering the lobby, but doing so upside down.  I was struck by how bizarre their gait was.  It almost looked exaggerated, like the Monty Python Ministry of Silly Walks.  Why?  Very simply because we mentally impose a smoothness on our perception of human gait that, in reality, does not exist.  People DO bob up and down as they walk, but we see them as maintaining a steady height.  It's like "psychological compression".

What does that have to do with using ring modulation to achieve octave doubling?  Guitar signal is MUCH less stable, and much more inconsistent than we like to think of it as being.  Pick a string and we "hear" the note as stable and consistent...but it isn't.  Do a Pete Townsend "windmill" when you hit a power chord, and you will introduce a momentary pitch bend.  Indeed, there are many instances where we introduce more pitch deviation than we think we do.  We also don't want to double EVERYTHING.  We want the note fundamental doubled, but not all those harmonics.  And the harmonic content changes, depending on the string/fret, as well as where we are in relation to initial pick attack, because harmonic content changes as the string settles.

So the simpler, and more pleasing outcome, is to "filter" the guitar signal, by using the neck pickup with the tone rolled back, pick higher up on unwound strings, where there is less harmonic content, drive the daylights out of that signal, and hopefully double the note fundamental, with much less doubled harmonics to create haze.

I'll just add that, when Aphex used the signal-modulating-itself strategy for doubling frequency content, it applied this to a signal that had been seriously hipass-filtered, such that the result was only top end.

[amptramp]

When you apply a signal to a multiplier, everything in the signal is multiplied by everything else.  We talk about harmonics in a guitar signal but in fact, most "harmonics" are not exact multiples of the fundamental frequency.  In an electric guitar, stiffness of the strings leads to the harmonics being slightly sharp.  In an acoustic guitar, the 2nd, 3rd and 4th "harmonics" are flat due to detuning caused by delivery of energy to the resonant hole in the guitar body.  You end up with sum and difference frequencies that are not related musically and it ends up being messy.  Some researchers call the slightly detuned multiples "partials" rather than harmonics.

I had thought at one time you could build an exponentiator circuit for audio based on the log / antilog circuit in the National Linear Applications Handbook in AN-30.  This gives you the ability to generate a sliding scale of exponents so if instead of squaring a signal, you want an exponent of 1.5 (tube sound!) or 3, it is just a potentiometer adjustment to get it.  Theoretically, you could get negative exponents so you could get a half-frequency output from an exponent of 0.5.  It might work for a sine wave but a signal is a different beast entirely.

One place where frequency mixing was used to achieve a lower frequency was in the Minshall Model E organ.  They were faced with the prospect of using tube dividers from a top frequency oscillator but they didn't want to extend the number of dividers just to generate the pedal frequencies so they did something interesting.  They mixed a second harmonic (an octave above the desired frequency) with the musical fifth above the second harmonic (third harmonic) to get the lower octave so if you want C an octave down, you mix C an octave above that with G above the C you already have and the difference frequency is an octave down because the G is three times the frequency you want.  It worked because to get a pedal signal, you use a lowpass to muffle all the other mixing products.

[Digital Larry]

I just fired up SpinCAD Designer and used the Multiply block to see what it would sound like with some clean guitar chords going in on both sides.  It sounds "sort of" Ring Mod-ish.  It doesn't sound "good" to me, but hey.  I also tried it with some sine wave tone bursts and indeed it does seem to generate a clean octave from that.  I followed it with a 1-pole high pass to block the DC.  This took all of 5 minutes.

The main point I am trying to make though, is that you could, wasting nothing but some time, experiment with the simulator in SpinCAD Designer to see what if anything sounds like you'd like to build it up.  There's also a Ring Mod block with a built in carrier oscillator. It doesn't put me out at all if you wish to implement your ideas using analog circuitry, though certainly that could sound different than the FV-1 simulator built into SpinCAD or an actual FV-1.

DL

[diffeq]

I just fired up SpinCAD Designer and used the Multiply block to see what it would sound like with some clean guitar chords going in on both sides.  It sounds "sort of" Ring Mod-ish.  It doesn't sound "good" to me, but hey.  I also tried it with some sine wave tone bursts and indeed it does seem to generate a clean octave from that.  I followed it with a 1-pole high pass to block the DC.  This took all of 5 minutes.

The main point I am trying to make though, is that you could, wasting nothing but some time, experiment with the simulator in SpinCAD Designer to see what if anything sounds like you'd like to build it up.  There's also a Ring Mod block with a built in carrier oscillator. It doesn't put me out at all if you wish to implement your ideas using analog circuitry, though certainly that could sound different than the FV-1 simulator built into SpinCAD or an actual FV-1.

DL

Is there any kind  of frequency analyzer or fundamental extractor function in SpinCAD? by that I mean things othr than a zero crossing detector.

[Digital Larry]

Not at the moment but if you manage to develop such a thing in FV-1 assembly code I'd be willing to turn it into a block.

DL

[patricks]

Yeah, there's a crazy chip from Alfa which would do this job, three times over!!

https://electricdruid.net/datasheets/AS3363.pdf

Quite what you'd *do* with three ring mods in one box is not clear to me, but it's pretty remarkable. (The obvious application for such a thing is in the mod matrix of a analog synth, allowing different modulation signals to be affect different things with either polarity and variable depth). Perhaps Amptramp's frequency shifter is an example?

Simpler dual VCAs like the AS3360 or AS3330 would also do the job.

Oh my gosh, that's mad! I love it!
I'm imagining now a ring mod/trem circuit, the input is buffered, then split three ways. The first signal path is into one of the three VCAs/4 quadrant multipliers, the second and third get split using high and low pass filters and through each of the remaining two VCAs/4 quadrant multipliers. With a "range" switch on the oscillator frequency the lower speed range acts as a harmonic tremolo on the two split inputs, and at higher speed range you've got one ring mod that with a modulator signal closer to the fundamental (should be more consonant), and another further away (should be more dissonant).
Put a level pot on each signal before a mixer/buffer stage and you've got the ability to blend between almost regular trem and harmonic trem, or for the ring mod any combination of the harmonic series on the output, from almost consonant to super weirdy! That's the concept, anyway...

Turns out I've been blathering on about the same stuff for a long time, now!
https://www.diystompboxes.com/smfforum/index.php?topic=59881.0

This fellow is demonstrating his build of the EPFM RM with an envelope follower governing the modulating frequency, such that when he digs in, the sum and difference get farther apart and more dissonant; an interesting idea.  But, thinking it over, and given that the EPFM design provides for mixing of the RM and clean sound in an op-amp mixing stage, another approach could use and envelope follower to dictate how much of the RM tone is mixed in with the clean sound.  Put an LDR in parallel with the fixed resistor bringing the RM into the mixing stage (and raise the actual value of that resistor from what the EPFM schematic shows), and an envelope follower could drive the LDR+resistor value down, when you dig in, and make the resulting tone more "boing-ey".

I know, I've been learning a lot about ring mods and ring mod-alikes reading some of your past posts - thank you
The envelope follower idea is very cool. The idea of using the envelope follower to blend between clean and ring mod-ed sound is great. I might try a simple mash-up of the Logan 5 with the envelope follower from the Dr Q with Jack Orman's mods for a relatively simple build and see what it can do. Should be fairly simple to put that together on breadboard or vero

... if it's followed by a filter (as would be typical on a synth) then that's not necessarily a problem.

On that note, I've had this idea for a "smooth but cheap" ring modulator that wraps a square wave / switched-inversion / analog-XOR type ring modulator with pre- and post-filtering; either a pre-/de-emphasis scheme (differentiate -> chop -> integrate is equivalent to ring modulation with a triangle wave), or perhaps matched band-pass filters on the input and output so as to modulate a more restricted band of signal (I would expect this to be more amenable to dry-blending).

Or, you could go the other way; fuzz up the guitar signal and use the squared up signal to chop a low-harmonic carrier waveform (and either the carrier or output would need to be gated by transitions of the fuzzed-up signal, as it never itself goes to zero).

I'm wondering a similar thing, would that approach get you something musical-sounding using a square wave fuzz? I'm tinkering with a comparator fuzz at the moment, so this has me curious

One place where frequency mixing was used to achieve a lower frequency was in the Minshall Model E organ.  They were faced with the prospect of using tube dividers from a top frequency oscillator but they didn't want to extend the number of dividers just to generate the pedal frequencies so they did something interesting.  They mixed a second harmonic (an octave above the desired frequency) with the musical fifth above the second harmonic (third harmonic) to get the lower octave so if you want C an octave down, you mix C an octave above that with G above the C you already have and the difference frequency is an octave down because the G is three times the frequency you want.  It worked because to get a pedal signal, you use a lowpass to muffle all the other mixing products.

Is this different to divide-down synthesis, or a similar concept with different execution?

I just fired up SpinCAD Designer and used the Multiply block to see what it would sound like with some clean guitar chords going in on both sides.  It sounds "sort of" Ring Mod-ish.  It doesn't sound "good" to me, but hey.  I also tried it with some sine wave tone bursts and indeed it does seem to generate a clean octave from that.  I followed it with a 1-pole high pass to block the DC.  This took all of 5 minutes.

The main point I am trying to make though, is that you could, wasting nothing but some time, experiment with the simulator in SpinCAD Designer to see what if anything sounds like you'd like to build it up.  There's also a Ring Mod block with a built in carrier oscillator. It doesn't put me out at all if you wish to implement your ideas using analog circuitry, though certainly that could sound different than the FV-1 simulator built into SpinCAD or an actual FV-1.

DL

That's a cool concept! I've downloaded the zip file from GitHub, I'll see if I can work out how to install it over the weekend or during the week next week (I haven't installed things off GitHub before, I'll need to figure out how to go about it

[Digital Larry]

I just fired up SpinCAD Designer and used the Multiply block to see what it would sound like with some clean guitar chords going in on both sides.  It sounds "sort of" Ring Mod-ish.  It doesn't sound "good" to me, but hey.  I also tried it with some sine wave tone bursts and indeed it does seem to generate a clean octave from that.  I followed it with a 1-pole high pass to block the DC.  This took all of 5 minutes.

The main point I am trying to make though, is that you could, wasting nothing but some time, experiment with the simulator in SpinCAD Designer to see what if anything sounds like you'd like to build it up.  There's also a Ring Mod block with a built in carrier oscillator. It doesn't put me out at all if you wish to implement your ideas using analog circuitry, though certainly that could sound different than the FV-1 simulator built into SpinCAD or an actual FV-1.

DL

That's a cool concept! I've downloaded the zip file from GitHub, I'll see if I can work out how to install it over the weekend or during the week next week (I haven't installed things off GitHub before, I'll need to figure out how to go about it

There's no installer.  The ZIP should contain a JAR file.  Extract it.  This JAR is a Java program.  You'll need to have the Java Runtime installed.  Let me know if you face any issue.

[amptramp]

One place where frequency mixing was used to achieve a lower frequency was in the Minshall Model E organ.  They were faced with the prospect of using tube dividers from a top frequency oscillator but they didn't want to extend the number of dividers just to generate the pedal frequencies so they did something interesting.  They mixed a second harmonic (an octave above the desired frequency) with the musical fifth above the second harmonic (third harmonic) to get the lower octave so if you want C an octave down, you mix C an octave above that with G above the C you already have and the difference frequency is an octave down because the G is three times the frequency you want.  It worked because to get a pedal signal, you use a lowpass to muffle all the other mixing products.

Is this different to divide-down synthesis, or a similar concept with different execution?

In the Minshall Model E, the idea was to avoid having additional octave dividers because they used single triode dividers for each frequency and there was enough trouble keeping these dividers stable.  These were not dual triode downcount flip-flops, they were tuned stages where they turned a triode off until the second trigger pulse came from the previous triode.  They had enough trouble with five octaves - they were not about to try this with more octaves and larger capacitor values.

By going to the mixing / frequency multiplication method, they got more octaves out of the five divider stages without adding another divider for each note (there are 36 12AU7's used for dividers) and this made for a cheaper solution.  The difference frequencies were where they wanted them to be and the sum frequencies were obliterated with filtering.

[patricks]

Wow, that seems like a lot of triodes - but then I've never really considered tone generation in valve instruments before.
The mixing and filtering approach is very clever, though

I've been thinking more about adapting the EHX Frequency Analyser, with a hi/lo switch for the frequency range and an AS3363.
http://dirtboxlayouts.blogspot.com/2021/03/electro-harmonix-frequency-analyser.html
Looking at the schematic it seems to me that two possible places to put a switch in the ICL8038 function generator circuit are either at the resistor in parallel with the 250K frequency pot (to choose between the stock 200K and a lower value) or at the frequency capacitor on pin 10 (although I'm not sure whether it would be a higher or lower value).
The schematic lists the frequency pot as 250K CCW, does that mean reverse log, or wired backward?

Also in the datasheet for the ICL8038 through a buffer/splitter it looks like the output is buffered so it should be fine to take a three way split of the carrier signal direct from the output to each of the quad multipliers in the AS3363, but it wouldn't be much hassle to add a simple buffer/splitter stage if need be

Larry, I've PM-ed you about SpinCAD

[Digital Larry]

OK I was wrong.  There's no longer a ZIP file with a JAR in it. 

Download the JAR directly from this page:

https://github.com/HolyCityAudio/SpinCAD-Designer/releases

[patricks]

Got it! Thank you

[soggybag]

The EHX Ring Thing is a sort evolution of the Frequency Analyzer. It does everything from standard ring mod sounds to tremolo, and vibrato like sounds. I don't quite understand what's going on. It's four quadrant multiplier and gives you access to each of the four quadrants. This provides vibrato and pitch shifting type sounds. It's super musical and also has the classic ring mod sounds.

[patricks]

Cool!
I had a look for a schematic but couldn't find one (it was only a quick google search, though). I did find this archive of ring mod schematics on the Experimentalists Anonymous site, though: https://experimentalistsanonymous.com/diy/index.php?dir=Schematics/Ring%20Modulators%20and%20Frequency%20Shifters

[John Lyons]

The EHX Ring Thing is a sort evolution of the Frequency Analyzer. It does everything from standard ring mod sounds to tremolo, and vibrato like sounds. I don't quite understand what's going on. It's four quadrant multiplier and gives you access to each of the four quadrants. This provides vibrato and pitch shifting type sounds. It's super musical and also has the classic ring mod sounds.

Wow. Ring Thing sounds great and is DEEP.
I hadn't really heard it before somehow.

[eh la bas ma]

I built this ring modulator from Parasit Studio, and i can recommend it :

https://www.musikding.de/xorcist_1

https://www.parasitstudio.se/uploads/2/4/4/9/2449159/xorcist_2_doc.pdf

There are two internal trimmers, Gate and Sensitivity, both are also very useful wired as external controls.

Not sure if this is exactly what you are looking for, but this project is cheap, sounds very good, and it will get you started in your Ring Mod Quest.

Only downside on this project is that you can't use the Ring Mod without the Fuzz. The Fuzz itself sounds amazing though, and you can blend it with the modulated signal. You can dial out the Fuzz signal with Blend fully CW, but the ring mod signal is fuzzy, a bit like an octave up/down circuit with the Blend control fully CW, set to cut the clean signal out of the mix.

Don't know if you are familiar with octavers, but those i tried tend to have also some more or less synthetic/glitchy/Lo-Fi octave sounds.
I mean, it's kind of dirty compared to a perfectly clean guitar signal.

From what i could understand, it's part of the analog nature of the process ?

Other good point is the momentary footswitch, allowing to toggle stuttering mod on or off. When it's off, the modulation acts a bit like an octave up/down effect, depending on how you dial the Frequency control. There' s also 2 internal switches, best wired as external toggleswitches in my opinion, allowing to change the action of the momentary switch (more info in the build docs). You can change the effect of the momentary in two different ways. Very useful to play with the effect while playing with the guitar.

On its own this effect sounds a bit raw, with some kind of Lo-Fi touch, but once combined with other circuits (reverb, delay, enveloppe filters...) it gets much more interesting and musical. It's also perfectly silent, no background noises. I often use a Meatball clone connected before it, and a Memory Man clone after it, with lots of feedback, for exemple.

I'd suggest to change all the internal trimmers and DIP switches into external controls.

[moosapotamus]

Arguably overly complicated, maybe, but still thought provoking and worth including in any ring mod conversation...

https://moosapotamus.net/files/stompboxology-ring-modulators.pdf

I've built a few different ring mods and the Frequency Analyzer is my current fave. Could just use some modulation!

[John Lyons]

I've built a few different ring mods and the Frequency Analyzer is my current fave. Could just use some modulation!

Modulating the carrier frequency?
Have you done this?

[moosapotamus]

Not yet. I've built a stock Frequency Analyzer and it already sounds great! Have been thinking that a Vactrol on one of the frequency pots would do the trick. Just drive it with an LFO and maybe even add switchable envelope control.