- Learn What FM Synthesis Is And How It Works
- Dive Into The History And Evolution Of FM Synthesis
- Understand The Strengths And Limitations of FM Synthesis
The modern world of sound design presents us with various approaches and creative opportunities. The four most common types of sound synthesis are:
- Subtractive
- Additive
- FM (Frequency Modulation)
- Wavetable.
This article will examine how FM synthesis works, its history and development through the decades, and some of its strengths and limitations in sound design.
What Is FM Synthesis?
FM stands for frequency modulation. The application of FM synthesis was conceptualized in the 1960s based on ideas used in radio broadcasting.
FM synthesis utilizes the manipulation of sound waves through specific routing algorithms.
When waveforms are combined, wave interference occurs, resulting in a hybrid wave that exhibits properties of both waves, explained further in my article on Additive Synthesis. With the addition of multiple waveforms, we can achieve complex outcomes in an extensive range of sounds.
Additive synthesis uses this concept; however, a fundamental difference in sequencing sets them apart. In additive synthesis, many waveforms with varying properties are stacked simultaneously. Each waveform collides with one another, resulting in a desired sound.
However, in FM synthesis, a waveform is explicitly routed to directly interfere with and thus modulate another waveform. We’ll dive into this in a bit more depth later.
Since the decades of FM synthesis’ conception, the approach has become much more complex, allowing us to create a broader range of sounds using this technique. The characteristics commonly associated with FM synthesis are lush evolving pads, gritty bass sounds, warm keys, and metallic bells and chimes.
However, FM synthesis can produce the sounds of wind instruments, resonating body string instruments such as guitar and violin, and even human vocal sounds.
Origins of FM Synthesis
Invented in 1933 by Edwin Armstrong, Frequency Modulation was a technique used to encode a carrier wave with audio information by altering its frequency with a modulator signal. Radio broadcasting was the main application of frequency modulation, and it allowed people to transmit high-fidelity sound, delivering news and important announcements to listeners.
Before FM broadcasting, AM or Amplitude Modulation broadcasting was used to transmit sound. However, amplitude modulation is more limited than FM when encoding sound and reproduces a less accurate version of the original source.
Additionally, with a greater frequency range, FM synthesis was less susceptible to interference from other signals and could be heard more clearly. This was an essential development in communication throughout the history of human civilization.
Decades later, in 1967, during his research at Stanford University, John Chowning discovered that he could produce frequencies over one million Hertz by using complex waveforms to modulate sine waves. Over the years that followed, Chowning developed an algorithm that allowed for synthesizing an exciting range of sounds.
This algorithm was licensed to Yamaha in 1973. They released the world’s first digital FM synthesizer, the Yamaha GS1, in 1980. By the early 80s, Yamaha’s DX7 synthesizer was making waves in the music industry and infiltrating the pop charts with full force.
New England Digital Corporation licensed the FM synthesis algorithm from Yamaha, releasing the Synclavier I in 1977. Artists like Kool & the Gang, Michael Jackson, Sting, Whitney Houston, and A-ha brought the sounds of FM synthesis to a worldwide audience.
With Yamaha’s monopoly on FM synthesis ending in 1995, as its patent expired, other companies could apply their own spin to FM synthesis. In the following decades, synths such as the Alesis Fusion, Korg Kronos, and Native Instrument’s FM8 have shaped FM synthesis.
How Does FM Synthesis Work?
Let’s look at how we can use frequency modulation to produce sound. Oscillators are used to generate the waveforms and are referred to in FM synthesis as operators.
The operator used to manipulate other waveforms is known as the modulator, whereas the waveform being modulated is referred to as the carrier.
In its simplest form, the signal flow in FM synthesis goes from modulator to carrier to amplifier. The amplifier is where the signal can be shaped over time using an envelope generator, creating either swelling sounds or shorter, plucky sounds.
FM synthesis can include multiple operators, creating a more complex variety of sounds. More operators generating waveforms allow for more potential outcomes. To further increase the possibilities of sound design, the sequence of waveform modulation can be altered in FM synthesis.
Below is an example of potential sequencing algorithms when introducing multiple operators. Modulators are shown in blue and routed to carriers shown in red.
Assigned to each operator is the Frequency Ratio parameter, which allows us to determine the relationship between the fundamental frequency of a note played and the operator frequency. For example, a ratio of ‘2’ will double the fundamental frequency. Frequency ratios do not have to be whole numbers. This allows us to explore interesting inharmonic relationships within each waveform.
Whole number ratios will produce harmonic frequencies of the fundamental, whereas decimal numbers will produce inharmonic frequencies with detuned sounds. The level of the operators can be adjusted to change the amount of each waveform that presents in the final output sound.
Formants were introduced into FM synthesis to emulate sounds made by the human voice and acoustic instruments like the cello, violin, or horn. Formants allow us to re-create the specific spectral patterns that define the sound of particular tools. This concept gives FM synthesizers with this feature the ability to recreate the sounds of an impressive range of instruments.
Pros & Cons Of FM Synthesis
Objective classification of the benefits and drawbacks of different synthesis techniques can be difficult due to their distinct approaches to shaping sound. However, specific defining characteristics and limitations of FM synthesis are worth noting.
| Pros Of FM Synthesis | Cons Of FM Synthesis |
| Complex routing algorithms | Complexity |
| Recreation of instruments | Overuse of presets |
| Harmonic precision |
Why Use FM Synthesis?
✔ Complex Routing Algorithms
The outcomes are endless, with many routing possibilities between carriers and modulators. Changing the signal flow at any point can quickly deliver new and pleasantly unexpected sounds.
✔ Recreation of Instruments
FM synthesis, with its introduction of formants, allows us to recreate a vast variety of sounds that emulate the timbre of real instruments, something that not all synthesizers are capable of. This gives producers access to sounds that would otherwise require an entire studio full of musicians.
✔ Harmonic Precision
Frequency ratio and operator level control allow us to adjust harmonic blends and introduce interesting detuned timbres. This makes FM synthesis favorable when synthesizing lush pads and rich metallic tones.
Limitations of FM Synthesis
Complexity
Compared to subtractive synthesis, it is worth noting that FM synthesis requires a certain level of patience. Although introducing more operators does increase a synthesizer’s capability, it also opens a new can of worms with each potential algorithm.
Overuse of Presets
During the height of the Yamaha DX7’s popularity in the 80s, the overuse of its available sound presets began to overshadow the expansive capabilities of FM synthesis. This was a common theme for FM synthesizers of the time, and many producers began to underestimate and, therefore, overlook FM synthesis.
Examples Of FM Synthesizers
Classic FM Synthesizers
Notable, classic additive synthesizers include:
- Yamaha D7X (1983)
- Synclavier I (1977)
- Alesis Fusion (2005)
Modern FM Synthesizers
Modern additive synthesizers, including VST plugins, include:
- Native Instruments FM8 (2006)
- Korg Volca FM (2022)
- Arturia DX7 V (2022)
Final Thoughts
Regarding FM synthesis, focus, understanding, and patience go a long way. FM synthesis can produce a vast variety of lush, texturally rich sounds and elevate your tracks to a new level. If you’re looking to brush up your knowledge on other types of synthesis, check out our other guides:
