What Is A Synthesizer & How Synths Work

Everyone knows what synthesizers sound like – from the big, dramatic synths of the 80s, to the synth bass and whistle-y hooks of 90s/00s hip-hop, to the washy sounds of modern indie and lo-fi.

You probably know what a synth looks like and you may even own one, but you may not know the nitty-gritty of what makes a synthesizer and how it works.

In this guide, we’re going to clear up what makes up a synthesizer, how they were invented and how you can use them to make sounds.

What Is A Synthesizer?

A synthesizer is an electronic musical instrument.

It is typically controlled with a keyboard and is capable of producing a variety of sounds.

This is accomplished by combining signals of different frequencies.

The first electronic sound synthesizer was built by American acoustic engineers Harry F. Olson and Herbert Belar at RCA.

This early synth was massive in stature, and was fed information encoded on a punched paper.

During the 60s, more practical synths were starting to be produced.

Notably, Robert Moog started developing Moog synthesizers.

The Moog III had two five-octave keyboards that controlled voltage changes.

Voltage changes in this case would control pitch, timbre, attack, decay – musicians then had nearly full control over the sound of the instrument.

This type of technology was the basis of modular and analog synthesis in the 60s and 70s, and the basis for all of the synthesizers that were built at the time.

Subtractive & Additive Synthesis

Most analog synths use subtractive synthesis.

Subtractive synthesis starts with a signal containing a fundamental tone and all of the overtones that signal contains.

Signals that have fundamental tones with overtones are called sawtooth-wave signals.

From there, you would use the different functions on the synth to change the tone – filter the high frequency information away or the low frequency information away.

Change the attack and release time, the envelope, etc.

Almost all analog synths you’ll find in a music store are analog, subtractive synths – Moogs, Prophets, etc.

There are also synths that use additive synthesis.

Often starting with a pure tone with overtones, like a sine wave, and then adding modulation or overtones.

These synths are often FM synths that add information to the tone via Frequency Modulation.

Additive synthesis is quite a bit more complicated than subtractive synthesis.

This guide will focus on subtractive synths first!

How Are Tones Generated?

Here’s a little physics lesson that will explain how synthesizers work.

Sound is caused by a vibrating object that changes the air pressure, and in turn vibrates our eardrum, which we then perceive as sound.

Guitar strings vibrate, and then we hear sound.

When a synth is generating this vibration, it’s called “oscillation”.

In a synth, oscillation is generated by rapidly changing voltages in a circuit.

When these oscillations are repeated, they create a “waveform”.

When recorded, the soundwave it will literally look like a wave – it is a visual representation of the  vibration and changes in air pressure that you hear as a tone.

A synthesizer generates these tones and then gives you the tools to further shape a sound’s pitch, tone and timbre.

Once the tone is shaped, it is then amplified inside the synth’s circuitry and sent to speakers or out of a cable and into a PA or a mixer.

In a nutshell: synths generate a tone by rapidly oscillating voltages.

The tone is then shaped with the controls on the synth, amplified in the synth and then sent out into the world.

How Do All The Knobs Work?

If an analog synth didn’t have a panel full of knobs on the front, it wouldn’t make anything resembling music.

Electrical signals can generate tones, but the tones they generate are not particularly pleasant.

They are very direct and can sound more like speaker feedback than music – organic waveforms generated by guitars and pianos are harmonically rich and much more complex.

But with a few edits to the sound, you can take the electrical signal and transform it into sounds you’ve heard on countless recordings, starting in the late 60s.

There are four basic components that work together to create sound.

They are as follows:

• Oscillator – this generates the waveform and changes its pitch
• Filter – filters carve out certain frequencies to change the way the waveform sounds
• Amplifier – before the tone leaves the synth, it is amplified to control the volume and touch
• Modulation – the tone can be sent through modulation to create effects like chorus and delay

Here’s a more in depth breakdown of these components.

Oscillation

The oscillator is what creates the sound – it is like fingers on a guitar string, lips on a tuba, etc.

Voltage from a power source oscillate electrons and creates a waveform.

You can choose what kind of waveform you create, because different waveforms create different sounds.

The most common waveforms are: sine waves, triangle waves, sawtooth waves and square waves.

The oscillation portion also controls pitch.

Pitch is called “frequency” in physics speak.

The frequency with which a waveform goes through a cycle of its pattern is measured in cycles per second, or Hertz (hz).

The faster the frequency, the higher the pitch.

440 Hz is an A note, 880 Hz is an A an octave higher.

260 Hz is middle C, 520 Hz is an octave higher than middle C.

Pressing down different keys will oscillate the circuit at different frequencies to generate different tones or notes.

That's how synthesizers turn voltage into musical notes!

Filter

It is interesting that a violin and a piano can play the exact same note (which creates a waveform of the same frequency) but sound completely different.

The is because of the sound’s timbre.

The filter is where you control the timbre of the sound and start working with harmonics.

A sine wave is a single frequency, but most sounds are made up of several frequencies to form the dominant pitch that arrives at your ear.

These other pitches are called harmonics.

They are not heard as pitches but as overtones that give a sound unique character.

All of the other waves (square, triangle, sawtooth, etc.) have a dominant pitch and a bunch of harmonics that give the waveform a big, fat sound.

The filter section modifies the timbre of the synth by blocking certain frequencies and letting others through.

Turning the filter knob up and down gives you this sound:

Amplifier

Synths can also manipulate a signal’s size by putting the initial tone through an amplifier circuit.

When the amp makes the waveform bigger, it becomes louder.

The cool part about this is not that it makes the waveform louder, but that it changes loudness over time.

How quickly the sound reaches peak loudness, how long the note sustains, how quickly it dies away.

Imagine a violin player lightly feathering the string, and then slowly digging in harder and bowing faster – they are controlling the amplitude of the violin in the same way you can control the amplitude of a synth.

Envelope

This loudness control is called an “envelope”.

Envelopes open and close and so do synth sounds.

The envelope usually has four controls (sometimes more) called ADSR, which represent the following:

Attack

Attack is how quickly the tone will sound when you press a key.

You can have the note immediately pluck, or have the note slowly appear over time, giving the synth a “washy” sound.

Decay

Decay controls when the sound starts to fade.

If you dial the decay all the way back, the tone will immediately disappear when you take your finger off the key, creating a very “tight” sound.

Leaving the delay open will create a delicate and long sound.

Sustain

Sustain is how long a sound will hold while you’re pressing the note down.

Release

Release controls when the note ends when you remove your fingers from the note.

The amplifier and envelope has a huge amount to do with what your synth will sound like.

Most of the tone lies in these controls.

Modulation

Different synths will have wildly different modulators that allow you to further craft a sound.

Often, the different modulation options are what differentiate one synth from another synth.

There are, however, a few modulation options that are standard on most analog synthesizers.

Here are a few common modulation options:

Low-Frequency Oscillator/LFO

This is one of the most common effects found on synths.

This oscillates a signal at low frequencies the ear can’t hear.

That's because it’s not used to create a sound you can a hear.

It’s used to modulate other parts of the synth to create modulation.

Applying an LFO to the oscillator (the first part of a synth) will create vibrato by wiggling the pitch around

Applying the LFO to the amplifier will create tremolo, where the volume goes up and down.

Applying the LFO to the filter is how you get the wobble bass sound often heard in dubstep, where the amplitude is going up and down and the filter is opening and closing with the LFO.

Ring modulation

Ring modulation combines two signal inputs to get different frequencies and overtones.

It creates a spooky, metallic sound that is used in movies frequently.

Other Types Of Synthesis

Subtractive synthesis is easily the most popular and common type of synthesis you’ll run into.

Begin with a harmonically rich tone generated by the oscillator, filter out various frequencies with the filter, and then apply effects and modulation.

However, there are other types of synthesis as well, which became more popular as synths and music evolved.

When synths were first created, they were modular synths – so named because each component, from the oscillator, to the filter, were all separate modules you had to manually connect with patch cables.

They were huge and cumbersome and expensive.

Synths took off in the early 70s when synths that were portable like the Minimoog came out.

This is an example of a subtractive synth.

With the introduction of portable synths, musicians could take them to gigs and the studio.

Synths were all over pop records, funk records, glam records, jazz, new wave and prog records.

In the 70s and 80s, a new synth started appearing in popular music.

FM Synthesis

Digital synths had algorithms instead of circuits.

This means you can program waveforms, stack them together and multiply them into almost any combination to recreate just about any sound imaginable.

This is when synthesizers got good at emulating organic instruments like trumpets, pianos, bass, guitar and more.

Synthesizers like the Yamaha DX7 were especially popular in the 80s.

These synths had preset sounds called voices or patches that came straight from the factory.

Very few people program their own sounds on FM synths because it is complicated.

Generally, you had to get into the settings of the synth to craft the sound.

Synths Today

Today, synths are enjoying a bit of a renaissance.

After the cheesy synth sounds of the 80s, grunge came around and almost killed the digital synth.

Artists who were using synths at all were back to using Moogs and other analog synths.

But we swung back towards digital synths in the early 2000s with the rise of softsynths (software synths), which enabled anyone with a laptop to pump out electronic sounds.

Again, we swung back to analog synths, with Moog, Roland, Korg and Prophets putting out reissues of their classic synthesizers.

There has even been a resurgence in modular synthesis amongs synth aficionados, who want to be in full control of their sound.

Currently, synths are in a great place.

What Is A Synthesizer & How Synths Work; Final Thoughts

So that's what synths are.

You can go out and buy a reissue of a classic synth that sounds very close to the old one but with modern features like the ability to save sounds.

You have access to tons of FM synths from the 80s for cheap on the used market.

Software synths are now better than ever, with companies like Arturia offering software versions of classic synths that sound very close to the classic synths they are emulating.

Boutique synth companies are offering absolutely wacky modular synth options for your nerdy pleasure.

And, on top of all that, there are innumerable hours of tutorials available online to help you create your perfect sound!