- Interested in synths but confused by the jargon?
- What are the different types of synthesis?
- Get a head start with our handy cheat sheet!
Navigating The Types Of Synthesis
In the world of synthesis, there are a wide range of approaches we can take when it comes to generating sounds from scratch. The most common ones have confusing names like wavetable, FM, additive and subtractive synthesis. The truth is, it’s hard to describe how a whole method of synthesis works with just a simple label.
Most modern synths incorporate a few styles so it’s important to get a feel for the most common approaches. Having said that, your synth will still lean into one style more than the others.
We’ll look at these terms and explore where they come from and what they mean for producers and sound designers.
This is the best one to start with as the concept is quite basic and it’s responsible for a lot of classic synth sounds.
The idea behind subtractive synthesis is you start with a sound that is rich in harmonics, then you use filters to remove frequencies in a more selective manner.
Often the oscillator sounds you start with are simple shapes like saw waves, square waves or even white noise. A lot of sounds can be made with just a single oscillator, but combining two or more oscillators will create much richer sounds.
We of course use modulation sources such as LFOs, envelopes and velocity to affect the oscillators and filters to shape our sounds. This is not exclusive to subtractive synthesis and we’ll talk about this more at the end.
After the sound is generated by the oscillators, it is processed with filters to shape the timbre. These are just like the filters you find in your DAW or on a parametric EQ except fine-tuned for synthesis, often emulating circuits in vintage synths.
For many early analog synths, lowpass filters were the only option. Now it is possible to have a huge range of filter types, all with unique quirks and characteristics.
Filters have two important controls – cutoff frequency and resonance. The cutoff is simply the point at which the filter starts working. If you have a lowpass filter with a cutoff frequency of 1200kHz, the sound will be progressively attenuated above this point.
Resonance is the ‘emphasis’ around this frequency, essentially just a narrow volume boost that gets louder with higher resonance settings. As the resonance approaches the maximum setting, you will hear what sounds like a tone centered around the cutoff frequency.
Resonance is the key to wah-wah effects and acid techno basslines.
Subtractive features like filters are extremely common on synths of all types. It’s hard to think of a better way to get such efficient control over the tone with so few controls.
What Does Subtractive Synthesis Sound Like?
Obviously this is subjective, but there is still some consensus as certain words get thrown around more often when discussing this style of synthesis.
Partly because of the association with analog technology, subtractive synths are praised for sounding warm and organic. The ‘natural’ feel could perhaps also be down to how voices in nature are shaped – the voice box generates a sound rich in harmonics and the mouth and body filter the sound.
Strictly subtractive synths tend to have a limited number of controls but will sound good no matter what settings are dialed in, as long as the oscillators and filters are good quality. There’s a place for almost anything made on a good subtractive synth if you keep an open mind.
Subtractive synths tend to sound:
For these qualities, subtractive synths are good for ‘reinforcement’ if other synth parts are thin, digital, or lifeless. They can add body and warmth to anything.
With wavetable synthesis, the focus is more on the oscillator than the filter. Most of the ‘heavyweight’ VST synths that are popular today feature wavetable oscillators.
Specifically, wavetable synths allow for a huge range of oscillator shapes beyond just simple saws, squares and triangles.
What’s more is you can have hundreds of wave shapes in just a single oscillator, and we call this collection of shapes a wavetable. Your synth oscillators are now free to make an incredible range of ‘animated’ sounds entirely on their own.
Wavetables are similar to sprite sheets in 2D video games, except with tiny bits of sound, usually no longer than 50ms at 44.1kHz. Played on its own, each frame sounds like a tiny click. But of course, your synth oscillators loop them to make tones!
Instead of creating chaos by playing all these shapes at once, we use a ‘position’ parameter to choose just one shape or ‘frame’ that is being played by the oscillator at any given time. We then modulate the position to create movement and ‘animate’ the sound.
Don’t worry – you don’t have to make your own wavetables if you want to play with wavetable synths! There are plenty of great libraries available on the net and your synth will come with a bunch as it is. But it’s fun and easy to make your own. Serum has a huge range of cool features for making your own complex wavetables very quickly.
Wavetables are most often distributed as WAV files (just like your samples) and will work in a number of different synths. Sometimes they are presented as folders of individual frames, but with Serum they are stored as a single file with all frames back-to-back.
Just drag one into your DAW like an audio clip and look at the waveform if you want to know what’s inside, it’s an easy way to learn in a matter of seconds.
It will sound weird on its own. This is because time and pitch are not inherent to wavetables – it’s up to your synth to figure out what position of the table to play at which frequency.
Because wavetables are high resolution sound waves, the pitch is naturally very low when you hear them as raw files. Serum uses 2048 samples (pixels of audio) per wave which allows for a huge amount of detail and a large number of harmonics per frame.
Wavetables can be just a few frames big, and your synth will fill in the gaps between the frames.
Sometimes you don’t want it to do this. In this case, you are probably using a wavetable that is intended more as a library of static shapes rather than a table that is supposed to be animated. There’s nothing wrong with this – you can still make great sounds with static tones!
What Does Wavetable Synthesis Sound Like?
Because wavetable synthesis is much more varied than subtractive synthesis, it’s hard to sum up as easily. When you can program a sound frame-by-frame and these frames can contain anything, a wavetable synth can really sound like a lot of things.
They can be perceived as cold and digital, but it doesn’t take much to warm them up either – usually unison on the oscillators will do the trick here.
They are capable of sounding:
- Harsh (think US dubstep basslines)
A good way to understand the fundamental idea behind FM, or frequency modulation, is to get a basic synth, initialize the patch so that it is a clean tone, then use an LFO to heavily modulate the pitch (or frequency) of the oscillator.
Now, increase the speed of the LFO to the fastest setting and notice how the oscillator morphs into an entirely new tone.
FM synths refine this process so that the results are much more harmonic and musical. But make no mistake, FM synthesis can sound like a complete mess if you’re not careful. On the plus side, this makes them capable of generating very unique effects!
Operators, Carriers and Modulators
Inside each FM synth is an array of ‘operators’, which are simply just oscillators paired with envelopes for their amplitude. While other types of synthesis will certainly let you use multiple envelopes for different oscillators, with FM synthesis it’s considered standard practice to pair the two together with one term.
These operators are arranged so that some are heard as you play a note, while others are not heard but instead change the tone of the ones you do hear. These operators are referred to as ‘carriers’ (the ones you hear) and ‘modulators’ (the ones that vibrate the carriers to create tones).
Here’s where it gets more complicated: you can also modulate your modulators with other modulators. So operators can have more than one role!
If we look at the ‘algorithms’ in Dexed, we can see arrangements of operators that go way beyond the simple LFO -> oscillator pitch example we started with. There are up to 32 different algorithms in Dexed, but FM8 lets you patch operators freely with a matrix.
We commonly use sine waves in FM synth oscillators as they give us the most precise control over the tone color. However, it is very handy to use other waveforms for brighter sounds and it helps cut down on the number of operators needed to generate a sound.
What Does FM Synthesis Sound Like?
FM synthesis is often criticized for sounding cold, sterile and alien. I would argue that this is just how they tend to sound but they do lean into these sounds well, which we can use to our advantage. But it’s also entirely possible to go the other way and avoid these terms completely.
The trick with getting FM to sound ‘warm’ is to simply use effects.
Adding chorus can really thicken things up. Because FM is all about mathematical precision with pitch, it doesn’t detune easily on its own. FM also really shines with reverb as certain spaces can really bring an FM patch to life and put abstract, alien sounds in real places.
Although modern synths still struggle to realistically emulate actual instruments without resorting to samples, FM can do a pretty good job with bell sounds. These sort of clean, sometimes inharmonic tones are right up FM’s alley.
FM synthesis features heavily in 90s video game music as many sound cards used it to create complex sounds with little processing power. The Sega Genesis is the most famous example of this.
It’s also worth noting that FM synths are great for old school house and techno. They are particularly good for bouncy bass lines and bright, digital leads. FM basslines were also very popular in 90’s dance-pop and RnB.
Some common descriptions of FM synths include:
- Silly or cheesy (seriously, some sounds will crack you up!)
I’ve saved this one for last because it’s not as common, but it can be very musical and rewarding.
Additive synthesis is effectively the opposite approach to subtractive synthesis. Instead of starting with a sound that is rich in harmonics, you create waveforms with only specific harmonics.
This level of harmonic specificity is similar to FM, but we are given direct control over individual harmonics without the ‘broad strokes’ of FM. The downside is it takes a lot more work to create complex and evolving sounds with additive synthesis.
You’ll have some sort of graph to draw in harmonics and often phase as well. Your synth converts this to a waveform that your oscillator uses.
In many cases, you just draw them in with your mouse, which can seem tedious. But more advanced synths will have tools to save you from having to do everything yourself, and they may also have ‘frames’ of additive shapes just like wavetables.
For this reason it is not as common and many synths have additive features whilst not being truly additive themselves. For example, Serum allows you to use additive synthesis to generate frames for your wavetables.
What Does Additive Synthesis Sound Like?
Additive synthesis has a bright, musical quality that lends itself well to crystalline leads, glassy pads and techno basslines. Hammond and other organs employ a type of additive synthesis, so it’s no surprise that this method is particularly useful for mellow organ chords and the like.
It can also sound quite similar to FM except more elegant and refined as inharmonic sounds are more easily avoided. But the type of crystal clear bell sounds that FM synthesis can produce are also quite possible with additive synthesis.
Some common terms used to describe additive synthesis are:
Finding Common Ground
In reality, these approaches consist of only a few vital steps but lead to a whole universe of sounds with small adjustments.
Despite some fundamental differences, there are still plenty of similarities between these approaches to synthesis.
This is what makes it possible for synth manufacturers to incorporate and mix up different approaches and still maintain some level of familiarity.
Common features between these synthesis types:
- They are all made for music. This means they take notes from your keyboard and produce tones that correspond to the key pitch.
- They all have oscillators, and the sound always starts here.
- They all have LFOs, envelopes, velocity and other familiar modulation sources.
- They can all be polyphonic. There is nothing restricting you to just one note at a time.
- They can all be used for bass, leads, pads, SFX and anything you want. Some types lean more towards certain sounds than others, but that doesn’t mean they are only for certain sounds either.
Many of us will have a preference for one type of synthesis and we’ve covered enough of the common methods to help you figure out what yours is. That said, it’s silly to pick just one style and stick with it.
You don’t need to program all your sounds from scratch, but it’s still helpful to know what these terms mean so you can better understand the tools you use and why they sound like they do.