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Types of Synthesis: Wavetable, FM Synthesis and Others Explained
There’s a huge number of inspiring synthesizers out there. Every year more new exciting products hit the market.
But learning how to use even one synth is hard enough. It seems like every different machine takes time to figure out.
It doesn’t have to be intimidating though.
The number of new instruments is always growing, but there’s actually only a few different methods of synthesizing sound.
That means you only need to understand a few key concepts to know how most synthesizers work—and how to use them to get the sounds you’re looking for.
In this article I’ll explain the most common types of synthesis, what they’re good for, and what they can do for your sound and workflow.
Additive Synthesis
Additive synthesis is the process of adding sine waves together to synthesize new timbres.
It’s a good place to dive in because it’s surprisingly easy to understand.
Additive synthesis is based on the principle that any sound can be expressed as a sum of simple sine waves.
Additive synthesis is based on the principle that any sound can be expressed as a sum of simple sine waves.
That means that any timbre, no matter how lush or complex, can be synthesized by combining enough sine waves of different frequencies and amplitudes.
This had big implications for the earliest generation of synths.
Pioneering electronic instruments like the Hammond Organ and Telharmonium used this method to create their iconic timbres.
Sounds that are closely related to sine waves (like the pipe organs the Hammond was trying to imitate) are easier to generate with additive synthesis.
Tones like bells with inharmonic overtones and noisy, complex attacks are more difficult.
That’s why most modern additive synths are digital—You need a lot of horsepower to run enough individual sine oscillators to create highly complex sounds.
But today’s VST plugins are definitely up to the task. Modern additive synthesis is robust and cable of some truly amazing sounds.
Here are some examples of additive synthesizers:
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Subtractive Synthesis
Subtractive synthesis is the method of starting with a harmonically rich waveform created by an oscillator and attenuating it with a filter to create your desired timbre.
This type of synthesis is the most commonly used. It’s associated with the classic synths that started it all.
The waveforms most commonly used in subtractive synthesis is are square, saw, sine and triangle..
A square wave has a naturally rich, buzzy sound with lots of overtones.
But if you apply a low pass filter to it, the upper harmonics will be cut or subtracted from the sound, leaving you with something closer to a sine wave.
That simple concept is the basis of subtractive synthesis.
Combine this with an envelope generator to create changes in amplitude over time and an LFO to create modulation and you have a surprisingly wide range of possibilities.
Today’s subtractive designs have roots in the classic circuits that defined the synthesizer as we know it today.
That makes them great for creating classic analog-style leads, pads and basses.
Here are some examples of subtractive synthesizers:
FM Synthesis
FM or Frequency Modulation is a synthesis method that changes the timbre of one wave by modulating it with another.
The first commercially available FM synth was the massively popular Yamaha DX7 which basically defined the sound of the 80s. Compared to other forms of synthesis FM is fairly young.
If the “FM” part of FM synthesis is sounding familiar, you’re on the right track. FM synthesis uses the concept of carrier and modulator waves just like FM radio.
From there things get a bit complicated. Instead of oscillators, filters and envelopes, FM synths have operators.
Operators are essentially little self-contained synths with their own oscillators and envelopes. They modulate each other, but unlike LFOs, their frequencies are in the audible range.
This means that modulating one operator with another results in a change in timbre rather than a modulation effect.
Adjusting the frequency and amplitude envelope of the operators results in changes to the sound that can be pretty unpredictable.
Get six operators together in various combinations and there’s a lot of potential!
FM synths excel at creating inharmonic timbres and complex attacks. That’s why they’re often used for bells or electric pianos.
FM synths excel at creating inharmonic timbres and complex attacks.
Here are some examples of FM synthesizers:
Wavetable Synthesis
Wavetable synthesis is a method of synthesizing sound using sample-based waveforms as oscillators.
Instead of traditional oscillators, wavetable synths load each individual slice of a digital sample into a “cell” in a table.
Instead of traditional oscillators, wavetable synths load each individual slice of a digital sample into a “cell” in a table.
The synth scrolls through the slices in the table one by one to output the sample as a sound.
Different pitches are created by speeding up or slowing down the sample lookup rate.
This unique style of tone generation allows for some interesting possibilities.
Sample lookup in a wavetable can go backwards, forwards or only scroll through a portion of the wavetable.
Wavetables aren’t limited to the traditional synthesis waveforms and can be cascaded into each other. That makes them great for creating evolving timbres and rich textures.
Here are some examples of wavetable synths:
Other types of synthesis
With the most common synthesis methods out of the way, there are a few outliers that are worth mentioning.
These types of synthesis are related to the other styles I’ve covered, but with some differences that make them unique.
Phase Distortion
Phase distortion is an offshoot of FM. Its relationship to frequency modulation is complicated, but several interesting instruments have been produced using the technology.
The excellent Casio CZ series are the most well known phase distortion synths.
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Physical Modelling
Physical modelling is a synthesis method that uses mathematical models to approximate simple physical behaviour like a string vibrating or air blowing across a tube.
This style fell out of favour when samplers became advanced enough to convincingly emulate acoustic instruments, but it can be interesting for creating impossible acoustic timbres.
Ableton Tension is an innovative modern physical string modelling synth.
Granular Synthesis
Granular is a variation on wavetable synthesis where samples are broken down into microsecond fragments called “grains” and rearranged and manipulated.
Granular synths are capable of summoning incredibly lush and detailed textures from even the simplest samples.
Granular synths are capable of summoning incredibly lush and detailed textures from even the simplest samples.
Robert Henke’s Max4Live Granulator II is a great example of a free granular synth.
Synthesthesia
We’re so spoiled for choice in the free VST era that it can be a struggle to figure out which tools are right for the job.
With a little knowledge of the types of synthesis, you can learn anything synth by looking under the hood, rather than just checking out the paint job.
So now that you know how they work, go find the style of synthesis that best suits your music production flow!
Michael Hahn is an engineer and producer at Autoland and member of the swirling indie rock trio Slight.
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