Learning about additive and subtractive synthesizers is a must for anyone looking to get into synths. As the first types of synths ever made, they’re the pioneers of electronic music.
And they aren’t just ancient history! Additive and subtractive are used all the time in modern music production.
So keep reading if you want to take your songs to the next level with incredible synth sounds. I’ll show you how these synths work and give you a few tips about how you can use them creatively.
This is the second article our “Synthesizer 101” series. The first guide of the series covered the basics building blocks of the synth.
If anything in this article confuses you, I probably talk about it there. Check it out below!
And don’t forget to grab my FREE synthesizer cheat sheet. It’s got all kinds of helpful tips that’ll have you making synth sounds in no time!
The first additive synths were made in the early 1900s, making them the earliest synths to hit the scene. When synths were all analog, additive was most famous for powering electric organs.
Additive was the secret recipe behind famous keyboards like the Hammond Organ.
Additive synthesis is all about combining different sounds to make a new one.
Think of it as a painting. To make a detailed portrait, the painter works in stages.
First, she’ll throw down some basic colors to create the background. In the second coat, she’ll add in the general outline of the person she’s painting.
Then she starts getting more precise. She’ll meticulously add in layer after layer of brushstrokes.
On their own, these layers all look pretty simple. But when you stand back and look at the full picture, you see a super realistic image of a person.
Additive synthesis uses the same idea. You layer a bunch of simple sound waves to create a sound that’s way more complex.
The only difference is instead of adding new coats of paint, you’re adding more frequencies.
Additive synths usually have multiple sine wave oscillators. Sine waves are the simplest type of sound out there.
Most sounds are made up of a bunch of different frequencies.
When you pluck a guitar string, you’re not just hearing one note. There are tons of higher, quieter frequencies layered on top of it.
These higher frequencies, called harmonics, shape the tone of the sound. It’s these harmonics that decide whether an instrument sounds warm or cold, round or sharp, and so on.
But a sine wave is just one single frequency.
They might use the simplest sound possible. But by layering sine waves on top of each other you can make some really wild sounds with additive synths.
By combining sine waves at different frequencies, you can make all kinds of new sounds.
Additive in Action
But enough theory. Let’s see for ourselves how additive actually works. Here’s Logic Pro’s Alchemy synth with just one oscillator on.
The oscillator is making a sine wave, which sounds like this:
If I add two more sine waves, I can make a totally new sound.
I’ll set one of the new sine waves to be an octave higher than the first. The other will be two octaves higher.
By turning down the volume on these new sine waves, I can blend them in so they sound like harmonics on top of the lower one.
Now our synth sounds way sharper than the lone sine wave we heard before.
And that’s just three sine waves! Additive synths usually have tons of oscillators, giving you plenty of tonal options.
Additive synths allow you lots of control over the sound you’re creating.
You’re literally handpicking which frequencies to include, so it’s easy to hone in on a sound you like.
Want a more advanced look into what you can do with additive synthesis? I recommend checking out this video from Benn Jordan:
But for now, we’ll move onto subtractive synths!
Subtractive synths are probably the most popular ones out there.
So additive is about adding frequencies to make a new sound. That means subtractive is focused on cutting frequencies out.
If additive synthesis is like painting, subtractive is more like sculpting. Starting with a huge hunk of rock, you gradually chisel away at it, revealing the sculpture within.
In subtractive synthesis, you start with a sound that already has tons of harmonics. Using filters, you cut out any frequencies you don’t want.
Since you have a rich sound to begin with, subtractive synths don’t need many oscillators to sound huge. Usually it only needs one to three oscillators to make all kinds of exciting sounds.
Subtractive Synthesis in Action
If my song needs a bass synth, I can make one quickly and easily with subtractive synthesis.
First, I’ll pick out a sound wave that’s got plenty of frequencies to work with.
Logic’s RetroSynth lets me use two oscillators at once. So I’ve gone ahead and picked out two saw waves.
Together they sound like this:
As you can tell, there are still a lot of higher frequencies in there. If I tried to use this as a bass, it’d end up clashing with the rest of my mix.
That’s where filters come in!
By putting a low pass filter on the synth, I can make sure it only plays lower frequencies.
Instead of calling them high pass or low pass filters, many synths shorten it to HP or LP.
The number after the letters describes how strong the filter is.
A higher number means a stronger filter. So LP 24 will cut out more frequencies than LP 12.
The cutoff determines where the filter starts cutting. So when I turn the cutoff down, I get rid of more higher frequencies.
By selecting a low pass filter and turning the cutoff way down, I’ve honed in on a nice bass sound really quickly. Here’s what those two saw waves sound like now:
I could even make a cool effect using this low pass filter. By automating the cutoff up and down, I can make the synth sound fuller during big sections of the song.
Most subtractive synths have more options than just low pass and high pass filters. Bandpass filters cut out both high and low frequencies.
Comb filters make small pockets throughout the frequency spectrum. That creates deep cuts on a bunch of isolated frequencies.
Both of these sound way different than a high pass or low pass filter. Check out the different filters on your synth of choice and see what they all sound like.
Getting Creative with Additive and Subtractive Synthesis
Nowadays, most synths aren’t just additive or subtractive. Most synths combine ideas from either additive or subtractive with another type of synthesis.
For example, a lot of wavetable synths use subtractive synthesis.
We’ll cover wavetable synths later, so no sweat if you don’t know what they are. The main thing you need to know is that you can use filters in other kinds of synths to shape their tone.
Don’t like the mid-range of the synth you’re working with? Pop open a filter and cut some frequencies out!
A lot of sample-based synths let you use additive synthesis to totally change how the sample sounds.
For example, I can load a sample into Logic’s Alchemy synth and tell it to reconstruct the sample using additive synthesis.
This means Alchemy will automatically recreate the sample using sine waves. This is called “resynthesis.” The result is a more digitized version of the original sample.
Conclusion: Additive Synths and Subtractive Synths
And that’s how additive and subtractive synthesis works!
Additive is all about adding simple sounds together. Subtractive filters frequencies out of a sound that’s already complex.
As you keep working with synths, you’re definitely going to run into both of these methods.
Finding yourself confused as to how either of them work? Come back to this article for a refresher on these fundamental types of synths!
And be sure to grab my FREE synthesizer cheat sheet. It’s got a glossary of synth terms and a bunch of tips for making your own synth sounds.
Stay tuned for the next article in this series, where we’ll be talking about the sound of the 80s, FM synthesizers.