What's the difference between FM, Ring Mod, and Cross mod?

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Rex Coil 7
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What's the difference between FM, Ring Mod, and Cross mod?

Post by Rex Coil 7 » Mon Apr 22, 2013 9:26 pm

I was missing my old Korg Mono/Poly lately (sold it in 2003 for $660, paid $25 for it in 1987) and I got to thinking about the really nice modulation methods it used. Since then I've been pondering on that quite a bit.

So, having set up the pretense ....

What is the differencee between:

** Frequency Modulation (with audio range modulators, such as the DX-7 made famous).

** Ring Modulation (more of an "AM" thing, right?).

** Cross Modulation (uh .... ??)

I've been thinking of creating a modulation matrix for my modular. I have five VCOs (a dot com based system btw) and I've been wondering how difficult it would be to emulate some of the Korg Mono/Poly's cross mod + sync routings.

Anyhow .... so what are the basic differences between those three modulation types?

Thank you.
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Post by Rex Coil 7 » Tue Apr 23, 2013 1:49 am

Thanks.

But I wonder how these compare to cross modulation? Most FM has both VCOs tracking 1v/oct at the same time, does cross modualtion keep one VCO static while the other is tracking 1v/oct? Kindof like RM but without the RM circuit being involved?

Korg insisted that x-mod was not the same as RM (which I guess is easy to see how it isn't), and while XM is ~technically~ FM, I don't think XM is precisely the same, in that the modulation VCO doesn't track 1v/oct like it does in FM.

At least I think that's how XM works. But then again that's why I posted this thread ... to see what others had to say about it.

:)
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Post by CursedFrogurt » Tue Apr 23, 2013 6:58 am

Rex Coil 7 wrote:
Korg insisted that x-mod was not the same as RM (which I guess is easy to see how it isn't), and while XM is ~technically~ FM, I don't think XM is precisely the same, in that the modulation VCO doesn't track 1v/oct like it does in FM.

At least I think that's how XM works. But then again that's why I posted this thread ... to see what others had to say about it.

:)
X-Mod is just two oscillators FM'ing each other at the same time. Nothing extra special about it. Tends to produce much more enharmonic and unpredictable results.

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Post by Rex Coil 7 » Tue Apr 23, 2013 8:27 am

CursedFrogurt wrote:
Rex Coil 7 wrote:
Korg insisted that x-mod was not the same as RM (which I guess is easy to see how it isn't), and while XM is ~technically~ FM, I don't think XM is precisely the same, in that the modulation VCO doesn't track 1v/oct like it does in FM.

At least I think that's how XM works. But then again that's why I posted this thread ... to see what others had to say about it.

:)
X-Mod is just two oscillators FM'ing each other at the same time. Nothing extra special about it. Tends to produce much more enharmonic and unpredictable results.
Well, there's really nothing extra special about anything we do with these modulars .. I mean I've often said the world's greatest modulator is the patchcord (see my sig). I guess I'm just trying to figure out what Korg did with the Mono/Poly in that regard.

Hmm ... Perhaps I'll repost this with a different tack on the idea.

Thanks for the help!
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Post by Dr. Sketch-n-Etch » Tue Apr 23, 2013 3:20 pm

FM is frequency modulation: one oscillator modulating the frequency of another. If the frequency can go all the way to zero and come out the other side in "negative" frequency space (positive frequencies, but with the waveform inverted) then this is "through-zero FM" which has a distinctively rich and deep sound.

AM is amplitude modulation: one oscillator modulating the amplitude of another.

RM is ring modulation: this is essentially through-zero AM. Analogous with through-zero FM, now the amplitude goes through zero and into negative amplitude space -- the amplitudes are positive and the waveforms are inverted. (This is technically much, much easier to achieve than TZFM.)

XM is cross modulation: Now, the oscillator being modulated is modulating the modulator back.
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Post by Rex Coil 7 » Tue Apr 23, 2013 11:32 pm

Dr. Sketch-n-Etch wrote:FM is frequency modulation: one oscillator modulating the frequency of another. If the frequency can go all the way to zero and come out the other side in "negative" frequency space (positive frequencies, but with the waveform inverted) then this is "through-zero FM" which has a distinctively rich and deep sound.

AM is amplitude modulation: one oscillator modulating the amplitude of another.

RM is ring modulation: this is essentially through-zero AM. Analogous with through-zero FM, now the amplitude goes through zero and into negative amplitude space -- the amplitudes are positive and the waveforms are inverted. (This is technically much, much easier to achieve than TZFM.)

XM is cross modulation: Now, the oscillator being modulated is modulating the modulator back.
Gotchya.

I totally worded my query wrong. I know what FM, AM, RM ~are~, I was just unclear what Korg had done with the XM setup in the Mono Poly.

Nice explanations though! :) Thanks for the help (everyone) and thanks for the Wiki links, as well as the descriptions of the various types of modulations. I appreciate the assistance, I feel smarter now.
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Post by digital_steve » Wed Apr 24, 2013 12:37 am

Dr. Sketch-n-Etch wrote:FM is frequency modulation: one oscillator modulating the frequency of another. If the frequency can go all the way to zero and come out the other side in "negative" frequency space (positive frequencies, but with the waveform inverted) then this is "through-zero FM" which has a distinctively rich and deep sound.

AM is amplitude modulation: one oscillator modulating the amplitude of another.

RM is ring modulation: this is essentially through-zero AM. Analogous with through-zero FM, now the amplitude goes through zero and into negative amplitude space -- the amplitudes are positive and the waveforms are inverted. (This is technically much, much easier to achieve than TZFM.)

XM is cross modulation: Now, the oscillator being modulated is modulating the modulator back.
What a load of bullshit

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Post by dragulasbruder » Wed Apr 24, 2013 2:38 am

digital_steve wrote:... It's how you hold your tongue when you twist a knob; that determines the result.
ahaha we should write a book of "tonal tongue exercises for the modular synthesist" and hawk 'em for a hundred bucks, sit back, watch our systems grow by the hour.
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Post by digital_steve » Wed Apr 24, 2013 4:22 am

What's this we shit? It's my gig.
I'll give you 10% max.
richard wrote:
MrBiggs wrote:serious instrument. What does that even mean?
I think it means you have to frown when you play it.
causticlogic wrote:Yeah, digital_steve spells "fun" with a capital FU...

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Post by jupiter8 » Wed Apr 24, 2013 5:42 am

Actually most of you are wrong. It depends on the synthesizer.
On the Oberheim OB-X for example cross mod simply means osc1 fm:ing osc2. Almost positive it's the same thing with the monopoly.

On a Roland JX8P where such tomfoolery isn't possible due to the construction of the DCOs, cross mod is simply a ring modulator.

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Post by digital_steve » Wed Apr 24, 2013 5:44 am

I love the fact you've intimated that Dr. Sketch-n-Etch is wrong.
Good luck with that.
richard wrote:
MrBiggs wrote:serious instrument. What does that even mean?
I think it means you have to frown when you play it.
causticlogic wrote:Yeah, digital_steve spells "fun" with a capital FU...

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Post by jupiter8 » Wed Apr 24, 2013 5:58 am

digital_steve wrote:I love the fact you've intimated that Dr. Sketch-n-Etch is wrong.
Good luck with that.
A man who knows so much about anything as he does couldn't possibly have learned all that without making a few mistakes along the way,learned from it and been greatful to the one who showed him the errors of his ways.

At least that's what i'm counting on..... :hihi:

It's in the schematics,all you need is to look and know what to look for.

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Post by felixer » Wed Apr 24, 2013 8:48 am

words are confusing :hihi:
the yamaha dx7 does not use FM (as in frequency modulation) but it uses PM (as in phase modulation. yep, just like the casio's). really :mrgreen:
'cross modulation' doen't mean much in practice except 'something is being modulated'. could be sync too. taken literally it should mean: a->b and b->a, just like the dr said 8_) . things get unstable and chaotic pretty soon, so not too many commercial/mainstream machines have that.
results are what matters:
-with FM and PM you get extra harmonics, spaced with the freq of the modulator, around the freq set by the carrier. the deeper the mod the more harmonics you get. you may lose the carrier freq if mod depth is high.
-RM gets you two freq: sum and difference of the two inputs. everything else is 'bleed' which a good designer tries to minimise.
-AM gets you those two freq plus the carrier.

so they are pretty similar in the type of harmonic structure. one could argue that a good ringmod gives you the most flexibility in that it is the most controlled and you can decide at will if you mix in carrier and/or mod feq. or put several ringmods in series to create more harmonics. it is also the simplest/cheapest to built, so people on a budget should not dispair :mrgreen:

if you want to experiment i strongly recommend something like the doepfer a138m matrix mixer. very handy :tu:
don't need midi, don't need keys, just want knobs and cables (all together now ;-)

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Post by Eric G » Wed Apr 24, 2013 9:45 am

OK, checking the schematics now:

In the M/P X-MOD, VCO 1 modulates VCO 2,3 & 4. VCO 3 modulates VCO 4. This is exponential mod, so not true (i.e. linear) FM.

In the JX8P, DCO 1 AM:s DCO 2.

There you have it.

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Post by MitchXI » Wed Apr 24, 2013 3:04 pm

In a practical sense
these are all oscillator intermodulations

and will accentuate the difference in frequency between the two oscillators involved.

Personally,
I first think of how I'm going to create pitch differences between two oscillators (modulations, static spread, tracking error, etc.)
and then I'll apply either each and see how they sound

cross-mod will generally sound harsher than ring mod
But both will tend to mitigate your fundamental, create new harmonics based on the input harmonics, and generally sound aggressive, think a lot of new not-necessarily consonant partials.
Cross-mod will throw the modded osc out of pitch if you are keytracking
Ring Mod will not

phase-mod, i think it is practical to think of as through-zero junk in the module world
This will be similar to cross-mod, but should preserve pitch if keytracking


I personally class filter FM as related to these things. Done right, it requires two oscillators, and comes to life when they differ in pitch.
Filter FM tends to mitigate the fundamenal frequency a lot less, and tends to be generally more consonant.

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Post by Rex Coil 7 » Wed Apr 24, 2013 3:19 pm

OK ... there ... ya see what I mean? There is a LARGE difference between the textbook definition of what XM (or FM, or AM, or RM) is "supposed" to be, and what is actually employed or used by a given manufacturer.

This was my point all along. I just did a horrible job of wording it. I wanted to know what Korg did in the Mono/Poly that they ended up calling Cross Modulation. So wiki pages and textbook definitions that were provided weren't much use (I was already aware of those definitions).

The last several posts in this thread have demonstrated that point rather eloquently .... what label a given manuifacturer chooses to use to describe some function doesn't always align with textbook descriptions of said function.

I know what the Korg MP manual says, and I know what it sounded like (I owned one for a few years in the 80s), and I know what Korg called it ... I just wanted to know what it really was and how it compares to other forms of modulations that I am familiar with (knowing/learning that will help me to recreate the effect on my own modular synth). As I said I am trying to figure out if I can incorporate some of it into a modulation routing switch panel I am working up for my own MU based modular. I am trying to figure out if I can design a switching matrix to essentially create a Mono/Poly out of my modular synth (among other things).

Thanks to those that (unwittingly) described what I was getting at better than I did. And thanks to those that provided some help towards actually figuring out what Korg did.

I appreciate the help. :)
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Post by DKDiveDude » Thu Feb 01, 2018 8:57 pm

From the manual of the Korg Radias (page 84);

"Cross Modulation uses the output waveform of oscillator 2 (the modulator) to modulate the frequency of oscillator 1 (the carrier) at high speed to produce a modulated sound....Cross Modulation varies the pitch from the basic pitch for an equal distance up/down in terms of frequency."

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Post by moremagic » Fri Feb 02, 2018 6:05 am

CursedFrogurt wrote:
Rex Coil 7 wrote:
Korg insisted that x-mod was not the same as RM (which I guess is easy to see how it isn't), and while XM is ~technically~ FM, I don't think XM is precisely the same, in that the modulation VCO doesn't track 1v/oct like it does in FM.

At least I think that's how XM works. But then again that's why I posted this thread ... to see what others had to say about it.

:)
X-Mod is just two oscillators FM'ing each other at the same time. Nothing extra special about it. Tends to produce much more enharmonic and unpredictable results.
generally, yes, but on the mono/poly the "XM" is just regular fm where one vco modulates other vcos (no feeding the other vcos back to the one modulating)

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Post by moremagic » Fri Feb 02, 2018 6:11 am

MitchXI wrote:I personally class filter FM as related to these things. Done right, it requires two oscillators, and comes to life when they differ in pitch.
Filter FM tends to mitigate the fundamenal frequency a lot less, and tends to be generally more consonant.
filter fm is amplitude modulation, but only of some of the harmonics the vco produces instead of all of them; running a sine wave into a filter and fming it should be p close to am'ing it through a vca (2 quadrant, a ring mod will be different because it inverts the carrier when the modulator goes negative instead of just shutting up)

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Post by sduck » Fri Feb 02, 2018 10:38 am

when a 1 post wiggler necrobumps a 4 year old thread, then.... oh, never mind.

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Post by Rex Coil 7 » Fri Feb 02, 2018 11:16 am

sduck wrote:when a 1 post wiggler necrobumps a 4 year old thread, then.... oh, never mind.
Funny thing is, many replies in this thread are attempting to say that some corporation's use of the phrase "cross modulation" is a technical term. It may be, however it's actually just a marketing thing that only has Korg's own definition behind it.

It's like saying "Finger Lickin' Good" has some technical description attached to it.

Korg's use of the phrse "Cross Modulation" is not a technical description. It's a phrase they used to market the Mono/Poly that doesn't actually have much to do with whatever is technically correct about "'cross modulation".

Having authored this thread just under FIVE years ago, I now know that Korg's use of that phrase has little to do with any real technical aspect, but it looks REALLY KEWL on the control panel of the Mono/Poly (or as Marc Doty pronounces it ... the Monopoly ... y'know, like the board game).

Mmmmm..... X Mod .... looks so bitchin on my synth.

I am NOT NOT NOT .. so NOT .. saying that the Korg Mono/Poly's "X Mod" feature isn't real, or isn't useful, or isn't an actual modulation ... uh ... type. I am saying that that phrase is so loosely defined it could actually mean any number of things. Push the "X Mod" button and all kinda of super cool stuff happens, no doubt about it!

But do carry on, everyone. The opinions are interesting, and I've picked up a thing or seven in this thread. It's kinda like this old Chevy truck I had ... if it tries to die on ya ... just give it a good kick and it will fire right back up again.

:lol: :lol: :lol: :lol: :lol: :lol: :lol:
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Post by DKDiveDude » Fri Feb 02, 2018 2:06 pm

sduck wrote:when a 1 post wiggler necrobumps a 4 year old thread, then.... oh, never mind.
So what it sounds like you are saying is that I because I am new to this forum, my opinion is disregarded, and if so it is very arrogant!

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Post by starthief » Fri Feb 02, 2018 3:10 pm

moremagic wrote:filter fm is amplitude modulation, but only of some of the harmonics the vco produces instead of all of them; running a sine wave into a filter and fming it should be p close to am'ing it through a vca
Filters also affect phase, so filter FM is a form of phase modulation as well as amplitude modulation. Which is, I think, a large part of why filter FM can sound very different with different filter designs.
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Post by sduck » Fri Feb 02, 2018 5:13 pm

DKDiveDude wrote:
sduck wrote:when a 1 post wiggler necrobumps a 4 year old thread, then.... oh, never mind.
So what it sounds like you are saying is that I because I am new to this forum, my opinion is disregarded, and if so it is very arrogant!
Not at all. It happens all the time. I wouldn't consider Korg's definition of cross modulation to be comprehensive though - in terms of modular synthesis it means quite a bit more than that limited description. Take 3 or more VCOs, start cross patching ins and outs, the results are the real deal cross modulation!

Here's some rather intense cross modulation that you won't be getting from a korg:

[video][/video]

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