HELP!!! Understanding Types of Modulation

I know what a modulation wheel does, that's not the type of modulation I need help with.

What I do need help with is understanding the difference between pulse width, cross, and frequency modulation. I've heard the terms before and I was wondering how they are similar or different.

If instead of typing an explanation you would rather post some links to webpages that explain those types of modulation, that would also be appreciated.

Obtain this machine:

It does all of the above.

Ah, is that a Waldorf Q? I didn't know they were yellow...

Welcome to the modulation morass:

What keyboard is on top? Is that a Virus Indigo?

DSI Monoevolver keyboard.

An evil li-el bastik.

No wonder I didn't recognize it.

As impressive your collection is, my question still remains unanswered - what's the difference between pulse width, cross, and frequency modulation?

An article on FM:

www.sfu.ca/~truax/fmtut.html

Cross modulation:

http://en.wikipedia.org/wiki/Intermodulation

Pulse width modulation:

http://en.wikipedia.org/wiki/Pulse-width_modulation

Ahh... morass.

Now that's a word seldom used. First time I've seen it used in english actually.

///j

Originally posted by pighood Welcome to the modulation morass:

PWM seems the easiest to understand. While FM is a bitch to get around for a beginner. It's best to have diagrams and sound examples.

How did you guys learn FM? Or did anyone

There's two levels of FM:

1: simple FM that can be done on analog synthesizers

2: Yamaha FM like on the DX7

Simple FM just entails modulating an oscillator at an AUDIO rate. Most LFOs have a maximum frequency that is below the audio range, so when modulating an oscillator you hear vibrato...a slow change in pitch over time. But if you can crank up the modulation frequency into the audio range it stops sounding like vibrato and you hear sidebands (new harmonics) in the signal.

"Cross modulation" as found in analog and VA synths is similar to FM. The difference seems to be if the mod response is LINEAR it's FM and if EXPONENTIAL it's cross modulation. Some synths offer both types of modulation.

Both methods can be used to create metallic and harmonically dissonant sounds.

FM demo here: the first part is a sine wave (filter in self oscillation) the second a VCO (sawtooth wave?), in both cases the LFO (triangle wave) starts in the low range and heads up into the audio range until it tops out at about 300Hz. You can hear the sideband frequencies shifting as I adjust the LFO frequency. The sideband harmonics get louder as I increase the LFO modulation depth. There is no filtering being done in the demo.

Ummh Piggy ...

Cross modulation is not intermodulation. See Meatball's post for the precise definition of cross-modulation.

Intermodulation is what happens when you send one note into a distortion circuit and it sounds nice (say middle c). Then you add second note and all hell breaks lose. The two signals are being intermodulated within the waveshaper/distortion circuit. That's where powerchords techniques com from. (Perfect fourths and fifths create pleasing intermodulation artifacts.)

Cross modulation is what Meatball described rather elegantly. Hope this helps someone.

Jerry

Exactly. The Yamaha DX / John Chowning kind of FM requires linear response. Most analog FM is exponential. However, many VA's offer both.

Jerry

In linear FM the wave being modulated keeps it's frequency but has it's phase modulated, resulting in overtones. This is John Chowning-Yamaha DX FM.

In exponential FM the actual pitch is modulated. This is what's on most analogs.

You don't need a Waldorf to experience both. A lowly Micron has them, as well as ring modulation... plus (very important) the ability to modulate the amounts with envelopes, LFOs, velocity, all kinds of things, so you can actually put them to musical use other than just gongs and racket.

Jerry you beat me to it...

i'm confused now. is it the other way around?

I have no idea why one is called linear and the other exponential, but that's the definition of both... from Alesis. I'm not that smart...

Originally posted by mrcpro I have no idea why one is called linear and the other exponential, but that's the definition of both... from Alesis. I'm not that smart...

On a graph a linear relationship would result in a straight line whereas an exponential one would result in a curve.

Excellent thread BTW guys - a always thought XM & FM were same (until now) - I know the difference between AM & FM RF frequencies but never thought about the difference with audio FM.

I've heard XM on my ER1 and Jupiter 6 I had, and the Virus has got FM, but which synths feature both so I can here the difference directly?

Alesis Ion/Micron

Yamaha AN200/PLG150-AN (AN1x has FM only)

Most modulars

I thought cross modulation was when you had feedback between 2 oscillators. Like each one FMing eachother.

so cross modulation is just exp FM?

On my JP-6, cross-mod means that osc 2 modulates the frequency of osc 1 but not the other way around. It is easy to hear when you tune osc 2 into the sub-audio range. It acts like an LFO with X-mod engaged. So from the sound of it I think that would be called exponential FM.

Originally posted by Meatball Fulton Most modulars

In the nord modular and G2 family, various oscillators have differing (linear and exponential) modulation inputs so you can mix things up.

These is a free limited version of the G2 available at the Clavia website if you want to try out some different modulation timbres.

Jerry

Thanks for the help, guys. It's really hard to guess what this stuff.

As always: USE YOUR EARS!!!

Way more important than understanding the physics behind the sound

I wanted to know what they did to make a choice for my next synth, since my current one has no FM or PWM capabilities.

My old MKS70 had some very nice Cross Mod. on it. I think if you went after something with nice PWM or XM, you'd be happy. FM (Yamahas) are a somewhat harder to use, and have a very unique sound that doesn't always fit into songs. But it's very cool for getting out-of-this-world type sounds.