FM Synthesis Overview

Frequency Modulation, That Thing No One Understands

Many people think of Frequency Modulation (or FM) synthesis as a super complex thing that no one can understand. Some people give up completely on it. Well, just like anything else in this world, if you just spend the time to learn it, you too can master the art of FM synthesis.

 In Subtractive Synthesis, you generally have a waveform played by the oscillator, and that waveform then goes through the filter, envelope and effects to the output. Any other waveforms produced by secondary oscillators do the same thing. That’s it. When an oscillator produces that waveform, nothing affects it directly, so the sounds are relatively predictable. In FM, that’s not the case at all. Depending on which synth you use, you can have a number of oscillators using their waveforms to modulate one or several waveforms to create a brand new waveform. I know this sounds confusing, but here’s a picture of what I mean. The letters A though F represent an oscillator (called an operator in FM) and each can send it’s waveform to the output (like F), or to modulate another operator (like E)

FM uses two types of waveforms called carriers and modulators. The carrier operator is the one (or several) waveforms that go to the output and can be heard. The modulators cannot be heard, since they do not go to the output, they only affect the carrier, and change it’s waveform. Here’s another example. The top line is a regular sine wave. The carrier is producing a normal sine wave here, and is unaffected by any modulators. The second line has one modulator, also producing a sine wave, that is modulating the carrier to create a new waveform. You can see the general shape of the carrier waveform, but it also has other smaller sine wave like properties that drastically change the sound.

Huh, That’s Not All That Confusing

That’s the basics of how FM works, and while it may sound complicated in writing, once you start playing with a couple of operators it’ll start to make sense. One thing to note though is that FM can quickly get out of hand, and it’s very easy to turn a good sound into noise. So when you’re starting out, try only using one carrier, and one or two modulators. Also make sure the amount is fairly low or you’ll end up with a terrible sound usually. Don’t let the complexity scare you off! You can create some amazing sounds with FM, so give it a shot!


Beginner – Open up your DAW’s FM synth, or use another one you have. If you have Serum, start by using the FM modulation available there. If you don’t have any of those options go download a demo version of FM8 or any other FM synth you want to learn. Start by activating one carrier operator and one modulator. Slowly bring up the amount until you get a sound you like, but be careful not to add too much. Then if you want to further modulate your sound, add a second modulator. Try making it affect the carrier signal and see how that sounds, then change it to affect the other modulator you previously added. Notice how different those two options are. Play around with the various waveforms available and try to create 3 or 4 presets and save them (if you have the full version of your synth.)

Advanced – Create several patches using 2-3 carrier operators, and if your synth allows it, have at least one of them self modulate. Make sure you have a couple of modulators in there too, and remember you can usually have operators modulate other operators as well as be a carrier.

Question: What did you think of FM synthesis before this video? How has your opinion changed? What sounds would you like to create in FM that would be difficult or impossible to create with Subtractive Synthesis? Remember if you’re unclear about anything, just ask me a question!