Join Evan Sutton for an in-depth discussion in this video Harmonics, partials, and waveforms, part of FM8: Frequency Modulation.
- Now that we've got the index of modulation down, I'd like to talk about the ratio. So, as I mentioned before, frequency modulation is essentially a system where we're creating sidebands and new partials. So we're creating new overtones and new aspects to the sound that can increase the brightness, that can change the identity of it, much like switching a wave form in an oscillator, except we're actually using a couple of very simple sine wave oscillators at this point to create something very complex. And we can really adjust it and be very very specific about how we want that sound to be, and how we want it to change over time.
Frequency modulation is really the opposite of any of the synthesis that we've done so far, especially the opposite of subtractive synthesis. Where we're taking something bigger and we're chipping at it using filters and envelopes and things like that. With frequency modulation, we're actually growing a sound, and we're creating these partials and these overtones, and all the things that give this sound identity, sort of from the ground up, it's very very cool. So we've got our index in order, and what I want you to know is that we use the index of modulation to set the number of overall overtones and sidebands that we have, okay? So, I don't want you to think about that too much while you're actually creating sounds, but its important that you know it in the back of your mind, that okay, we're going to create these sidebands using the index.
And as you can see, when I turn it up and down, we get more of them. But what we're going to use the ratio for is actually changing their position. So, there's a number of these overtones and then there is the overall position of the overtones, which really changes their identity and the way that the sound comes off quite a bit. So I'm gonna go ahead and simplify the envelope for A, a little bit. (electronic synthesizer) Okay, pretty simple sound. (electronic synthesizer) Now, I'm gonna change the ratio of A to two.
So now, we have a ratio of two for A and one for B. Typically with frequency modulation, you hear people talk about a carrier to modulator ratio. A carrier, in a frequency modulation setup, is the audio signal, and that's a word that you're going to hear with vocoding, with ring modulation, its all over the place. But B in this case, is the carrier, A is the modulator. So if we have a carrier to modulator to one to two, that's what its referring to. Okay, so here's a ratio of one to one. (electronic synthesizer) And then here's with a modulator ratio of two.
(electronic synthesizer) And we can keep going. (electronic synthesizer) (electronic synthesizer) And we can go up high as well. (higher pitched electronic synthesizer) Boy, we really can change the sound quite a bit. So as I mentioned before, the ratio is using what's called the harmonic series.
Okay, and these are overtones that are all over the place in music. When we hear a square wave, when we hear a saw tooth, when we hear a guitar string, its all different combinations of these harmonics, these overtones. Now, when we use ratios that are integers, that is whole numbers, its all zeroes to the right of that decimal point, we are gonna wind up with harmonic overtones. Meaning that the overtones we create that pop out are in line with the harmonic series. They're gonna sound in tune, maybe they sound a little bit harsh at this moment, because we have kind of a rough sound, but they're gonna be in tune.
We can create some sort of detuned things by using non-integer ratios. Let me demonstrate. So if I just take this guy (electronic synthesizer note) and hold him down (electronic synthesizer note) and I could just click and drag on the ratio down and detune it, (electronic synthesizer note lowers) you can hear that things kind of sound a little bit less pure, a little bit less in tune. And one might even say that it sounds a little bit more natural as far as some sort of organic material because frequency modulation is something that I look to, to create metallic types of sounds, among other things.
And metallic sounds that we use, and or hear in real life, aren't always so pure. Sounds a little bit electronic when things are right on money as far as the harmonic series are concerned. So its kind of cool that we have this ability to create something that's just a little bit off base. Its a little wonky, let's listen. (electronic synthesizer) And if I play a chord, (electronic synthesizer chord) we can hear that there's still those relationships in there, but because the harmonic series is kind of compromised there, it winds up sounding not quite in tune.
The reason why I'm telling you this is not because I want you to go out and create a bunch of sounds that are kind of not in tune, its because these are all the details that really do create the identity of your sound. As you're building things with frequency modulation, you're gonna want to kind of decide how in tune you want things to be. Maybe you want them a little bit out of tune, maybe you want them clangy, maybe you want them very pure, its totally up to you. But the cool thing is that we have so much control over what we're creating based on just using the index and the ratio.
And another thing that I will point out is that we can change the ratio of the carrier, (electronic synthesizer) but I will tell you, that often changing the ratio of the modulator, is going to have more of an effect on things. Especially when you're just starting out on a sound.
- What is frequency modulation?
- Reviewing the FM8 routing matrix
- Harmonics, partials, and waveforms
- Using operators
- Percussion programming
- Programming with the Arpeggiator