Frequency Modulation Synthesis 101: Create Super Crazy Sound

Frequency modulation synthesis (aka FM synthesis) is one of the wildest and most powerful ways to create sound. 

It can take a basic sine wave and turn it into glassy bell tones, electric pianos, deep basses, or even crazy metallic sounds that cut through a mix. 

Plus, it’s perfect for making full pads, sharp leads, and gritty textures that you just can’t get with subtractive synthesis.

As producers, knowing FM synthesis inside and out can seriously step up your sound design and help you make sounds that stand out. 

That’s why I’m breaking down everything you need to know, including:

• How frequency modulation synthesis actually works ✓
• The difference between FM and subtractive synthesis ✓
• Setting the right frequency ratio for smooth or wild sounds ✓
• How to turn a simple sine wave into a huge, complex tone ✓
• Using envelope generators to control how your sound evolves ✓
• The best FM synths, both hardware and software ✓
• Layering FM with subtractive and wavetable synthesis ✓
• Using feedback to add extra grit and edge ✓
• Tricks for creating full, evolving soundscapes ✓
• Much more about frequency modulation synthesis ✓

Once you get the hang of FM synthesis, you’ll be able to create your own sounds from scratch and dial in the perfect modulator settings.

Plus, shape leads, basses, and percussive elements that actually stand out. 

You’ll have full control over how your modulator and carrier signals interact 一 giving you endless ways to build full, expressive, and high-energy sounds.

This way, your tracks will hit harder, sound cleaner, and grab attention every single time.

What is Frequency Modulation Synthesis?

If you’ve ever messed around with FM synthesis, you already know it’s a completely different beast from what you’d find in a subtractive synth. 

Instead of starting with a familiar waveform like a square wave or saw wave and filtering out frequencies, frequency modulation synthesis is a little different.

It takes a basic sine wave and modulates the frequency using another signal (called a modulator signal) to generate complex tones. 

This gives you some of the most unique, harmonically full sounds possible, which makes FM synthesis good for everything from electric pianos and metallic percussion to crazy sounds that wouldn’t be possible with analog oscillators.

FM synthesis works by taking a carrier signal and modulating it with a modulator frequency, which essentially changes its pitch in real time. 

The speed and intensity of this modulating signal determine whether you get a subtle vibrato effect or an entirely new, chaotic texture full of overtones. 

By stacking multiple operators together in different ways (called FM algorithms), you can create complex timbres that sound nothing like the traditional waveforms we’re used to in subtractive synthesis or the like.

What makes FM synthesizer technology even crazier is that it doesn’t rely on filters the way subtractive synths do… 

Instead, it generates harmonics naturally through frequency modulation for more digital sound possibilities that will actually blow your mind.

This is exactly why classic FM synths like the Yamaha DX7 changed the game in the ’80s. 

Whether you’re making bell sounds, glassy pads, or even gritty basses, FM synthesis gives you a level of sound design control that analog synthesizers just can’t touch.

But here’s the thing: FM synthesis can be intimidating at first. 

If you’ve ever opened up a digital FM synthesis plugin like Korg Volca FM or Dexed, you might’ve been completely lost looking at the operator’s output, frequency ratio, and all the other sound synthesis settings. 

But don’t worry, that’s totally normal. 

Unlike subtractive synthesis, where you can just twist a filter cutoff and hear instant changes, modulating the frequency in an FM synth requires a bit more understanding. 

Once you get it, though, it completely changes the way you think about sound design, which is what I’ll be breaking down for you today.

How FM Synthesis Differs from Subtractive Synthesis & Additive Synthesis

To truly understand FM synthesis, it helps to compare it to subtractive synthesis and additive synthesis, which are the two other major synthesis methods used in music production. 

Subtractive synthesis is what you’ll find in most analog synthesizers, where you start with a rich waveform (like a square wave) and use filters to cut out frequencies. 

This works great for warm, classic synth sounds, but it has limits when it comes to creating complex waveforms like bell tones or metallic textures.

Additive synthesis, on the other hand, is all about stacking sine waves at different frequencies to build a new sound from scratch. 

It’s a super precise way to generate complex sounds, but it’s not the most efficient method because you need more than one operator playing at different frequencies to get the right balance of harmonics. 

That’s where FM synthesis comes in… It sort of bridges the gap by taking a basic sine wave and modulating the frequency of it to create harmonics dynamically.

One of the biggest differences between FM synthesis and subtractive synthesis is that there’s no filter needed in FM, which we touched upon a little bit in the previous section.

Instead, the harmonics are generated naturally by operator arrangements and modulator signals (which gives it a sharper, more digital sound). 

For example, if you wanted to create a bell sound on a subtractive synth, you’d have to stack oscillators, adjust a filter, and fine-tune the resonance. 

With FM synthesis, you just tweak the modulator frequency and adjust the envelope generator, and boom, you’ve got a perfect bell tone that cuts through the mix.

Another key thing to note is how FM operators interact. 

In subtractive synthesis, each oscillator is more or less independent, whereas in FM synthesis, one operator’s frequency directly influences another’s. 

This is what gives FM synths their signature metallic, glassy, and evolving textures.

You can also go way beyond the audible range and use a modulation oscillator running at audio rate to create entirely new harmonics. 

That’s why FM sounds so bright and punchy compared to subtractive synths.

NOTE: One drawback would be that FM synthesis can be harder to dial in because small parameter tweaks make a huge difference. 

If you turn up the modulation oscillator just a little too much, you might go from a sweet electric piano sound to a full-on chaotic noise machine. 

This is why FM often feels more mathematical than subtractive synths.

But like I said, once you wrap your head around FM algorithms, you realize it’s actually super flexible for designing everything from subtle tones to crazy sounds.

The Key Components of FM Synthesis

To really get the most out of frequency modulation synthesis, you have to understand the core building blocks that shape its sound. So, let’s break down the key components that make FM synthesis such a powerful tool in music production.

• Carriers and Modulators: The Building Blocks

At the heart of frequency modulation synthesis, you’ve got two key elements: 

• The carrier signal.
• The modulating signal. 

The carrier signal is what we actually hear—it sets the fundamental frequency of the sound, just like a standard oscillator in a subtractive synth. 

The modulator signal, on the other hand, doesn’t produce sound on its own; instead, it alters the carrier’s frequency to create new harmonics and complex tones. 

The modulator frequency determines how fast the modulating frequency effect happens, and if it’s within the audio range, it creates entirely new complex timbres.

This is instead of just adding vibrato. 

The ratio between the carrier signal and the modulator frequency (called the frequency ratio) is key…

Simple integer ratios (like 1:1 or 2:1) lead to harmonic, musical sounds, while odd ratios (like 1.37:1) create more dissonant, metallic textures. 

By stacking multiple carrier operators and FM operators, you can generate incredibly complex sounds that would be impossible with just a single modulation oscillator. 

This is why FM synthesis is so powerful 一 it’s all about precise, dynamic control over the harmonic content of a sound without the need for filters or analog oscillators.

• Operators and Algorithms in FM Synthesis

In FM synthesis, an FM synthesizer doesn’t just have one oscillator.

It uses multiple FM operators that can either modulate or act as carriers depending on the FM algorithm being used. 

Each operator’s output feeds into the next, determining how the final sound is shaped. 

For example, the Yamaha DX7 used six operators with different operator arrangements, for a wide range of tones, from classic FM synths to more experimental sounds. 

More modern FM synthesizers, like Korg Volca FM, might use four operators to make the process easier while still providing epic sound design options. 

The way FM algorithms arrange multiple operators dramatically changes the resulting sound: linear chains create stacked harmonic richness, while more branching structures let you mess around with unpredictable overtones. 

Bottom line, understanding how one signal affects another in these operator modulating structures is key to mastering frequency modulation synthesis.

• The Modulation Index (Controlling Timbre and Complexity)

One of the most important concepts in frequency modulation synthesis is the modulation index, which determines how much the modulator signal affects the carrier signal. 

The modulation index is calculated by dividing the modulator frequency’s amplitude by the carrier signal’s frequency.

The higher this value, the more complex waveform the sound will have. 

For example, if your carrier signal is set to 220 Hz and your modulator frequency is 440 Hz with a high amplitude, you’ll hear a bright, harmonically edgy sound full of overtones.

 

But if you lower the modulator frequency or its amplitude, the sound becomes smoother and less aggressive (pretty straightforward, right?).

This makes it useful for classic FM synths like electric pianos or glassy pads. 

• A modulation index of 2 or higher results in complex timbres
• Values below 1 create more subtle changes, similar to a vibrato effect rather than full-blown frequency modulation synthesis. 

The key to getting clean, controlled sounds is adjusting the modulation index carefully.

Too much can lead to chaotic, noisy textures, while too little may not be noticeable at all. 

If you’re designing bell sounds or metallic textures, crank up the modulation index and experiment with different frequency ratios to find the perfect balance.

How FM Synthesis Works (Step-by-Step)

Understanding the inner workings of frequency modulation synthesis is the key to mastering FM sound design. So, let’s break down how FM synthesis takes a basic sine wave and transforms it into a complex sound 一 starting with the simplest modulation and moving toward full harmonic control.

• Modulating a Simple Sine Wave

To get started with FM synthesis, the first thing you need is a basic sine wave as your carrier signal 一 this is the cleanest waveform possible, with no overtones. 

If you play a 220 Hz sine wave on an FM synthesizer, you’ll hear a simple, pure tone.

 

Now, introduce a modulator signal at 440 Hz, and instead of hearing two separate tones, you’ll start hearing sidebands.

Additional frequencies that give the sound more character and depth. 

Keep in mind that: 

• Increasing the modulator frequency beyond the audible range can create subtle shimmering effects.
• Lowering it to LFO speeds gives you a vibrato effect. 

The amplitude of the modulating signal controls how much the pitch fluctuates, and by tweaking it, you can go from a gentle tremolo to a full-on metallic FM sound. 

A carrier-to-modulator ratio of 1:1 produces a harmonic sound, while non-integer ratios like 1:1.5 generate more inharmonic, percussive textures. 

This is why FM synthesis is so mind-bending.

You’re not just adjusting pitch and filters like in a subtractive synth, you’re actually reshaping the harmonic structure of the sound itself (epic, right?).

• Creating Complex Waveforms with FM

Once you understand basic modulation, you can start layering multiple modulators to create complex sounds that go way beyond what a simple subtractive synth can do. 

Instead of using just one modulator, try adding a second FM operator tuned at 1.5 times the fundamental frequency to create a more detailed, evolving harmonic texture. 

If you increase the modulation oscillator’s amplitude, you’ll start getting ringing bell tones.

This is perfect for designing digital frequency modulation synthesis textures like metallic percussion or glassy leads. 

And, you can even use four operators in a 2:1 ratio (two modulators per carrier) for a super bright, cutting sound.

On the other hand, stacking them in parallel (instead of in a chain) can generate lush, evolving pads, so dealer’s choice.

NOTE: Playing around with feedback (where an operator modulating another operator also feeds back into itself) can create gritty, distorted textures, similar to what happens when you overdrive an analog oscillator. 

If you want a fat bass sound, try setting a carrier at 55 Hz with a modulator at 110 Hz, then increase the modulator frequency’s amplitude until you hear that signature growl. 

The key to designing great FM sounds is experimenting with operator arrangements, modulation depth, and frequency ratios to find the perfect balance between musical and more experimental/hybrid textures.

• Using Envelopes to Shape FM Sounds

In FM synthesis, the envelope generator plays a huge role in shaping how a sound evolves over time, just like in a subtractive synth.

But, with even more precise control over the modulation oscillator itself. 

Instead of just controlling volume (like a standard ADSR envelope in subtractive synthesis), an FM synthesizer uses envelopes to modulate both the carrier and modulator frequencies 一 determining how the sound’s harmonics develop. 

For example, if you’re designing a bell sound, setting a short attack (0-10 ms) and a moderate decay (500 ms to 1 second) on the modulator frequency’s envelope creates a sharp transient followed by a natural harmonic fade-out. 

If you want to lay down a fat bass, you might set a longer attack on the carrier signal while keeping the modulator’s envelope tight.

This way, the sound will start super clean and then gain harmonic fullness over time. 

A classic FM electric piano sound works by using a sharp attack on the modulator, creating a strong percussive hit, while the carrier fades out slowly, giving it that signature smooth decay. 

In complex timbres, using different envelope generator settings for each FM operator allows for evolving textures…

Like a pad that starts warm and slowly introduces glassy overtones. 

The trick to mastering FM sound design is to experiment with different attack, decay, sustain, and release (ADSR) curves to find the perfect balance between sharp transients and evolving harmonics.

PRO TIP: Another classic way to add expression to your FM sounds is by using pitch envelopes. Pitch envelopes can be applied to the carrier or modulator signals. This will let you create dynamic pitch changes over time.

It’s perfect if you’re looking to create expressive lead sounds or interesting sound effects (especially at the attack portion of your sound for percussive movement).

FM Synthesizers: Hardware & Software

When it comes to choosing the right FM synthesizer, you have two main options: hardware FM synths and software-based digital FM synthesis. 

If you’re into hands-on control, my favorite hardware synths are:

• Yamaha DX7
• Korg Volca FM
• The Elektron Digitone

All of them provide dedicated knobs and sliders, which makes it easier to tweak FM operators without diving through endless menus. 

The Yamaha DX7, with its six-operator architecture and 32 algorithms, is a classic FM synth responsible for countless 80s and 90s hit records.

It delivers iconic electric pianos, basses, and metallic textures. 

Meanwhile, the Korg Volca FM takes inspiration from the DX7 but simplifies it with three FM operators instead of six, so it’s very beginner-friendly.

But don’t underestimate it when it comes to delivering rich FM sounds, because it certainly does. 

If you’re all about digital sound design, my favorite software synths are: 

• Native Instruments FM8
• Dexed (free)
• Arturia DX7 V 

They’re all about deeper sound synthesis 一 giving you full visual control over operator modulating structures and frequency ratios. 

Unlike hardware, software FM synths let you automate modulator frequency changes directly in your DAW, so you can create evolving textures/dynamic modulations all day.

Whether you choose hardware or software, the key to getting the most out of frequency modulation synthesis is finding a synth that matches your workflow.

Whether that means hands-on knob twisting or precise DAW-based tweaking, it’s all about to you.

Programming Your Own FM Sounds

Getting hands-on with FM synthesis can feel overwhelming at first like I said.

However, once you understand how to modulate the frequency of a carrier signal using a modulator signal, things start to click. 

If you’re looking to create a classic FM bass sound, start with a carrier frequency of around 55 Hz (A1) and set a modulator frequency at 110 Hz (A2) with a moderate modulation depth.

This will give you that deep, punchy, growling tone that’s perfect for hip-hop and electronic basslines. 

A great trick for getting even more punch is using an envelope generator on the modulator frequency so the modulation starts strong and fades out.

This successfully mimics an analog-style transient. 

If you want to program expressive FM leads and pads, try using a carrier at 440 Hz (A4) with a modulator at 880 Hz (A5) and set the modulation oscillator to track velocity.

Meaning, harder keystrokes add more harmonic complexity (perfect for dynamic, evolving synth leads).

For FM synthesis for percussion & drums, set your carrier signal at 400 Hz or higher with a short envelope generator on the modulator to create snappy metallic hits, for:

• Hi-hats
• Snares
• Toms 

A bell sound can be achieved using a 1:2 frequency ratio with a modulator frequency of 600 Hz and a long decay on the modulator’s envelope generator.

This is how classic FM synths create those crisp, glassy tones. 

Finally, if you’re after complex, evolving textures, try adding multiple operators with different frequency ratios and routing them through various FM algorithms to discover unexpected harmonics. 

The key to programming FM sounds is experimentation…

Small adjustments to operator modulating structures and frequency ratios can result in entirely new sound design possibilities.

Advanced FM Sound Design Techniques

Once you’ve mastered the basics of frequency modulation synthesis, you can start pushing it further with advanced sound design techniques. So, for this last section, we’ll break down some more advanced tips, tricks, and techniques for shaping your FM synthesizer sounds into something even more unique/expressive.

• Using Feedback for Extra Grit and Aggression

One of the best ways to add grit and aggression to an FM sound is by incorporating feedback, which occurs when an operator modulating a carrier signal also feeds back into itself. 

In Yamaha DX7-style frequency modulation synthesis, you’ll often see Operator 1 or Operator 6 used for feedback.

This adds harmonic richness and even slight distortion when pushed. 

For example, setting a modulator frequency of 220 Hz with a feedback level of 40-50% can add a raspy edge to a bass sound.

It’ll make it more aggressive, which is perfect for modern electronic music. 

If you increase the feedback to 80% or higher, you’ll start getting more noise-like, distorted textures, which can work great for gritty leads or industrial sounds. 

A great trick is to use feedback on only one operator in a multi-operator patch, so you get a mix of clean and rough harmonics for better control over the final sound. 

NOTE: If you’re aiming for thick, analog-like textures, try setting a low carrier frequency (55 Hz or lower) and increasing operator feedback to around 30-40%, giving you a warm, growly tone that feels more natural than typical digital FM synthesis.

• Layering FM with Other Synthesis Types

Layering FM synthesis with other synthesis methods can help you create sounds that combine the best of both worlds. 

For example, if you’re working on a fat bass sound, you can layer a subtractive synth using analog oscillators with a sharp FM synthesizer tone.

It balances warmth and harmonic bite. 

A great example is layering a sine wave sub-bass from a subtractive synth with an FM synth lead, where the FM synth provides the grit and movement, and the analog synth fills out the low end. 

If you’re into wavetable synthesis, try running an FM sound through a wavetable filter or granular synthesis engine for more evolving, spectral movement in your sound. 

A hybrid approach also works great for pads and textures…

For instance, combining FM synthesis for high-frequency harmonics with subtractive synthesis for lush, analog-style filtering creates a sound that feels both digital and organic. 

If you’re using four operators or more in frequency modulation synthesis, try routing one operator into a granular processing unit for added movement, giving your final sound a unique hybrid texture. 

The secret to layering is carefully balancing modulation depth, frequency ratio settings, and amplitude envelopes so that both synth types complement each other instead of competing.

• Playing Around With Unconventional Soundscapes with FM

If you really want to push the boundaries of frequency modulation synthesis, experimenting with unconventional soundscapes is where things get wild. 

Instead of sticking to traditional carrier-to-modulator ratios, try using modulating signals at non-integer values like 1.37:1 or even irrational numbers…

This creates inharmonic, otherworldly textures that sound nothing like standard subtractive synth patches. 

You can also try granular synthesis combined with frequency modulation synthesis by resampling an FM sound and stretching it using grain-based playback for a surreal, evolving quality to your patches. 

If you want something even crazier, set your modulator frequency to an audio rate range above 10 kHz, then slowly increase its modulation depth.

This creates shimmering digital sound artifacts perfect for cinematic textures. 

Using a modulation oscillator tuned above the audible range and assigning it to modulate the operator’s frequency results in eerie metallic drones that constantly shift as you play. 

Another cool trick is to assign a MIDI controller knob to sweep the modulator frequency, which lets you morph between glassy, bell-like sounds and chaotic noise textures in real time. 

Finally, using four operators with complex waveform sources instead of pure sine waves can generate unexpected harmonics.

It will create evolving complex timbres that feel completely organic and unpredictable.

Final Thoughts

And there you have it: everything you need to know about frequency modulation synthesis and how to use it like a boss.

Remember, it’s all about understanding how carrier and modulator signals interact, choosing the right frequency ratios, and using modulation depth the right way. 

Plus, envelopes, feedback, and automation can take your FM synth patches to a whole new level, so keep that in mind as well. 

Just remember to never go overboard with modulation depth or use random frequency ratios without intention.

Otherwise, things will start to sound harsh, chaotic, and difficult to control in a mix.

And, as a special bonus, you’ve got to check out these Free Project Files.

It includes 3 invaluable project files that show you exactly how to create a professional beat from start to finish (and yes, that includes frequency modulation synthesis). 

It’s basically like having the cheat codes to making beats that stand out, hit hard, and get major attention. 

Whether you’re working on glassy leads, deep basses, or evolving pads, these project files will help you see FM synthesis in action inside a full track.

This way, you can apply the same techniques in your own beats.

Bottom line, when it comes to frequency modulation synthesis, it’s all about choosing the right modulator frequency, dialing in the modulation index, and layering FM sounds.

Just remember to experiment with different waveforms, automate modulation parameters, and use envelopes for better dynamic control. 

Plus, make sure to blend FM synthesis with other synthesis methods, tweak the filter cutoff for extra shaping, and practice integrating FM into your full mix.

It will take your sound design to the next level.

Bottom line, if you apply everything we covered, your tracks will always sound professional, unique, and full of movement. 

This way, your sound design will stand out, your beats will hit harder, and your production skills will be on another level. 

Until next time…