How FM Synthesis Works

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The FM in FM synthesis stands for “frequency modulation” – a cool method of audio synthesis (learn more).

At its heart, FM synthesis is all about playing with sound waves. It uses a “carrier” sound wave – the main wave – which gets changed by a “modulator” sound wave – a secondary wave.

But what makes this method of synthesis special in relation to other types is that it adds more sound instead of taking it away, like with subtractive synthesis. This makes the sounds richer and more lively.

FM synthesis is based on simple math that can be understood easily. Once you get it, you can control it in any way you want and get really creative.

By the end of this guide, you’ll have a complete understanding of how to use FM synthesis to design your own unique sounds for music.

The Basics of FM Synthesis

Frequency modulation uses frequency changes between two oscillators to make complex sounds from their basic waveforms.

A “modulating” (i.e. changing) wave, usually a simple shape like a sine wave, is used to change the frequency of a “carrier” wave which is the initial sound we hear. This modulation creates a new set of frequencies, or “sidebands.”

Thus, customizing your “operators” is a very important concept in FM synthesis. Each operator is like a basic unit that creates a waveform. These operators can act as carriers, making sounds we hear, or as modulators, which change the carriers’ frequencies.

By carefully controlling the operators’ settings, like their frequency ratios and modulation depths, sound designers can change the harmonic content of the sound in a precise but complex way.

What is Frequency Ratio

Frequency Ratio refers to the relationship between two frequencies – the carrier frequency and the modulator frequency. It’s a ratio that determines the overall timbre of the sound that is produced.

Imagine a seesaw where the carrier wave is like the bar of the seesaw that goes up and down. The modulator is like the person who pushes the seesaw.

The frequency ratio, then, is like the balance between the weight of the person and the length of the seesaw bar.

If the balance between both the carrier and the modulator are equal (a ratio of 1:1), the seesaw goes up and down smoothly. But if they are different (for instance, 2:1 or 1:2), the seesaw will move differently, creating a variety of different movements.

Likewise, when you adjust the frequency ratio of an FM synth, it changes how the shape of the waveform in unique ways.

A Complex FM Synth With Dozens of Knobs and Two Screens

What is Modulation Depth

Modulation depth refers to how drastically the frequency of the carrier sound wave is changed by the modulating signal.

A greater modulation depth will cause a larger change in frequency, resulting in a more complex and rich sound. On the other hand, a smaller modulation depth will result in a less noticeable change in frequency, creating a simpler and smoother sound.

In practical terms, increasing the modulation depth in FM synthesis could add more overtones and harmonic content to the sound, making it brighter and more complex. Reducing the modulation depth will make the sound purer and simpler, like a sine wave.

Think of it as the strength of the spice you add to a dish you’re cooking. A little spice (low modulation depth) subtly changes the taste, while a lot of spice (high modulation depth) can transform the dish entirely.

Algorithms in FM Synthesis

What makes FM synthesis so flexible is the ability to link multiple operators in different ways, known as algorithms. Each algorithm gives a unique route for modulators to affect carriers, leading to a wide range of sound possibilities.

Algorithms are the specific arrangements of carriers and modulators to create different tones or sounds. They are essentially the ‘recipes’ for creating sounds in FM synthesis. The algorithms determine the type of interaction between the carrier and modulator frequencies.

They are generally represented as a graph or a diagram where nodes represent oscillators and the connections between them represent modulation.

The specific algorithm used depends on the sound you’re trying to achieve.

Understanding Operators

Operators are the core “building blocks” in FM synthesis. They both make sounds and interact with each other to create the final sound. Each operator can be a modulator or a carrier.

Operators have settings that the user can change. These settings let the user set how the modulation works.

Users can also customize operators. They can change different settings of each operator like the waveform type, the frequency, and modulation depth.

Operator Functionality

Grasping the features and tweaking options of individual operators is crucial to fully use them in FM synthesis.

In an FM synthesizer, each operator has several settings that let you manipulate sound in detail.

By changing things like the waveform, frequency, volume and envelope someone who designs sound can shape both the harmonic content and dynamic behavior of the sound.

More advanced modulation techniques open up even more possibilities. For example, you can set operators to modulate themselves or to be modulated by multiple sources.

Closeup Screenshot of an FM Synth VST

Here are various operators found on FM Synths and how they function in the sound design process:

  1. Carrier Operators: These are the primary operators in FM synthesis. They generate the base sound or tone that we hear. In sound design, they are responsible for creating the original waveforms.
  2. Modulator Operators: These operators modulate the frequency of the carrier operators. They can dramatically change the sound by introducing new frequencies, shaping the tone, and creating complex waveforms. They are responsible for the timbral changes and the complexity in the sound.
  3. Feedback Operators: These operators can feed the output of an operator back into its input. They can create a wide range of effects from subtle changes in tone to extreme distortion and noise. They are mostly used for creating unique and interesting textures.
  4. Envelope Generators: These operators control the volume of the sound over time. They can shape the sound to create natural-sounding attacks, decays, sustains, and releases. They play a crucial role in making the sound feel dynamic and expressive.
  5. LFO (Low-Frequency Oscillators): These operators produce a low-frequency signal that can be used to modulate other operators. They are typically used to create vibrato, tremolo, and other periodic changes in the sound. They add movement and life to the sound.
  6. Pitch Operators: These operators control the overall pitch or frequency of the sound. They can be used to create pitch bends, glides, and other pitch-related effects. They are key in defining the melodic and harmonic aspects of the sound.
  7. Filter Operators: These operators can remove certain frequencies from the sound. They can be used to shape the tone, create resonance, and simulate the sound of different materials and spaces. They add depth and character to the sound.
  8. Pan Operators: These operators control the stereo placement of the sound. They can be used to create a sense of space and depth, and to position the sound within the stereo field. They contribute to the overall spatial perception of the sound.

Crafting Sound With Frequency Modulation

Sound designers often start with a fundamental frequency and incrementally introduce modulators, shaping the sound’s timbre by tweaking the intensity and rate of the frequency modulation.

This iterative process allows for precise control over the harmonic content of the sound, leading to the creation of everything from natural-sounding instruments to otherworldly electronic tones.

Practical Applications

FM synthesis is used in all sorts of music.

In electronic music production, specifically, FM synthesis plays a key role. It helps make unique lead sounds, deep bass sounds, and complex arpeggios that set this genre apart.

During live shows, musicians and sound engineers use FM synthesizers because they can change the sound quickly, on the fly. This lets performers change their sound to match the feel of each show, creating a new and exciting experience for the crowd.

Film scores and video game soundtracks also benefit from FM synthesis. Composers use this tool to share emotion and add depth to the story, creating changing sequences and background sounds that boost the visuals.

FM synthesis is best for creating complex timbres and sounds such as electric pianos, bells, and basses. It’s also great for creating evolving and moving sounds, metallic sounds, and for creating unique, complex sound designs. Additionally, it can produce very bright and harsh sounds, and is often used for synthetic drums.

Here are some common sounds generated using frequency modulation:

  1. Electric Piano Sounds
  2. Bass Sounds
  3. Bell-like Tones
  4. Brass Sounds
  5. String Sounds
  6. Percussion Sounds
  7. Lead Synth Sounds
  8. Pad Sounds
  9. Organ Sounds
  10. Marimba and Vibraphone Sounds
  11. Synth Pluck Sounds
  12. Flute and Wind Sounds
  13. Synth Drum Sounds
  14. Sound Effects and Noises
  15. Metallic Sounds
  16. Chimes and Celesta Sounds
  17. Synthetic Choir Sounds
  18. Harpsichord Sounds
  19. Glassy Textures and Tones
  20. FM “Growl” Sounds

Advanced FM Techniques

Advanced FM techniques let you play around with modulators and carriers to create deep and detailed sounds.

By trying out different frequency modulation methods, you can make sounds that are beyond the usual. These advanced methods use layers of operators and modulators can modulate themselves, leading to dynamic and changing harmonic content.

Fine-tuning sound color becomes a careful task. It involves exact changes to modulation depth and frequency ratios. This control lets you shape sounds very specifically, from soft whispers to loud growls.

Advanced FM also involves unique waveform changes. Traditional sine waves can be replaced with complex waveforms, which opens up a whole new range of sound options.

These techniques are very useful in experimental sound design.

The History of FM Synthesis

FM synthesis, or Frequency Modulation synthesis, has a cool history filled with exciting moments.

This way of creating sounds started in 1967 when John Chowning found out you could make dynamic sounds by changing sine waves. This was a big deal and it’s where FM synthesis started.

Then, Yamaha used Chowning’s idea to make something awesome – the DX7 synthesizer. This was a game-changer. It changed how people made and composed music.

The Yamaha DX7 Synthesizer

Don Buchla – known for pioneering the style of “west coast synthesis” – also played a big role in the early days of FM synthesis. He used the principles of FM in his modular synthesizers, which were part of the early testing of what would become a key tech in electronic music.

The DX7 was a big hit in the 1980s. It made FM synthesis popular and really important in sound design. You can hear its influence in lots of different music genres and even in video game soundtracks.

FM Synthesis Evolution

There were more changes to FM synthesis over time. People tried new things and were able to go beyond traditional sounds.

As these changes happened, trends in sound design also changed. This showed how important FM synthesis was around the world. Artists and producers used FM to make new kinds of music. They often mixed it with other methods to create mixed sounds.

Now, FM synthesis is not only a nod to the past but also a tool that keeps changing with the times. It keeps influencing trends in sound design today.

Here are some popular FM synths that have lasted the test of time:

Hardware FM Synths:

  • Yamaha DX7: This is probably the most famous FM synth – the originator – offering 6 operators and 32 algorithms.
  • Korg Volca FM: This is a compact, portable FM synth that can load DX7 presets.
  • Elektron Digitone: This is a modern, powerful FM synth that has a sequencer and effects built in.
  • Yamaha Reface DX: This is a compact, battery-powered FM synth with built-in speakers and effects.

VST FM Synths:

  • Native Instruments FM8: This software synth is a modern take on Yamaha’s classic DX7.
  • Arturia DX7 V: This is another VST emulation of the DX7, but with added modern features.
  • Dexed: This is a free VST that’s a nearly perfect replica of the DX7.
  • Ableton Operator: This is a powerful FM synth that’s built into Ableton Live.
  • u-he Bazille: This is a modular FM synth with a unique approach to FM synthesis.

What to Do Next

Thanks for reading this complete guide on FM Synthesis for beginners.

Next up, deep-dive into another area you’d like to learn about. We recommend learning about granular synthesis in this overview.

You can also read up on other types of synthesis below: