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Synthesizers explained: What they are and how they work

Synthesizers can be very daunting for a newbie, even one with musical experience. Suddenly, you have all these parameters to think about, controls you haven’t seen before, and no idea where to start.

Luckily, it doesn’t need to be daunting, and with some basics under your belt, you’ll be on your way to being a synth master. In this article, I will talk about how synthesizers work, the different aspects of a synth, different types of synthesizers, and much more; let’s go!

About me

James Nugent, author and contributor at Higher Hz

I’m a producer, sound designer, and synth enthusiast with over 20 years of experience in the music industry. I have a diverse passion for music that blends tradition and technology.

As such a synthesizer enthusiast, testing and demoing new hardware/software is something I spend a lot of time on.

Contents

Use these jump links to navigate to the desired section of the article.

What is a synthesizer?

In a nutshell, a synthesizer is an electronic instrument that generates a wide range of sounds using an electrical signal. Sounds range from emulating acoustic instruments to weird and wonderful bass, pad, lead, and percussive tones.

How does it work?

Think about how an acoustic piano creates sound. You strike a key, a hammer hits a string, the string vibrates, our ears then pick up the vibrations in the air and convert them to sound. The same can be said for acoustic guitar strings, etc.

Synthesizers don’t physically create those vibrations with hammers or anything like that. Instead, an electrical signal passes through a signal path to an amplifier. The amplifier then sends the signal through a speaker to create vibrations in the air that we hear as sound.

So, in short, a synthesizer mimics those vibrations through an electrical signal and digital or analog processing. I will cover this in more detail, don’t worry.

The origins of the synthesizer

Now that you have a basic understanding of what a synthesizer is, it’s a good idea to find out where it all started. Despite strange instruments like the theremin being around in the late 1800s and early synths being around in the 1950s, it was 1970 before we have seen a widely-available synth in the form we think of today.

In 1970, Bob Moog introduced the Minimoog, which became the foundation for all synthesizers that followed.

Minimoog Model D from early 1970s
Original Minimoog from the 70s | Image: Andrew Russeth

Explaining the working process

As I mentioned above, a synthesizer uses an electrical signal to mimic the kind of vibrations that acoustic instruments create. Synthesizers can seem more complicated than they need to if you are a newbie, but understanding the basics is easier than you think. Let’s start with the basic building blocks of audio synthesis.

Oscillators

Synthesizers can have one or multiple oscillators, and that’s where it all starts. Oscillators generate the raw sound that is then shaped by the other elements of the synth. In short, you can summarize an oscillator as the signal/sound generator.

Oscillating simply means something is moving back and forth, and in this context, it’s referring to voltages moving back and forth. You’ll often see oscillators labeled VCOs, and that stands for Voltage Controlled Oscillators.

Let’s say an oscillator is moving between +1 V and -1 V; the motion creates a waveshape, and it’s that wave shape that gives the tone its fundamental characteristics. Just to be clear, when I say waveshape, I’m referring to the way the signal moves between positive and negative.

Before we move on from oscillators, let’s look at some basic/common waveshapes. Apart from how they look on a screen, one of the important differentiators between waveshapes is harmonics. I won’t get into the harmonic series in too much detail, but a basic understanding will go a long way.

Whenever you hear a musical note, you also hear a series of harmonics/overtones triggered by the original note/frequency. For example, if you play an A4 note, the fundamental frequency is 440 Hz, but you also hear harmonics of that frequency at 2x speed, 3x, 4x, 5x, and so on, infinitely.

These harmonic frequencies (multiples of the original frequency) aren’t infinitely audible; only the first few will make a real difference to what your ears pick up. Now, as I look at different waveshape, you’ll see why harmonics are important.

Sine wave

sine wave
Image: Omegatron

A sine wave is often referred to as the fundamental waveshape: it’s what all others are based on. Sine waves are the simplest waveshape because they contain no harmonics at all. The fundamental frequency generated is all that exists in a sine wave.

When you look at a sine wave on an oscilloscope, you can see a smooth transition between its minimum and maximum values. That smoothness is reflected in the sound.

Square wave

square wave
Image: Omegatron

The square wave is slightly more interesting because it does contain odd harmonics. When I say odd harmonics, I literally mean odd numbers: the 3rd, 5th, 7th multiple, and so on. A square wave has a somewhat nasal quality to its raw sound.

Sawtooth wave

sawtooth wave
Image: Omegatron

The name sawtooth comes from the fact it looks like the blade of a saw when you see it as an image. A sawtooth wave increases from the minimum value to the maximum value in a straight line (or vice versa). It then reverts back to the first value sharply, creating the saw-like shape.

These waveshapes contain a significant number of even harmonics, making it unlike other common waveshapes. The resulting sound is often compared to reed instruments or even bowed/stringed instruments where the bow and strings create tension before snapping back.

Triangle wave

triangle wave
Image: Omegatron

As you’d expect, a triangle wave looks like a row of triangles. It rises and falls in a series of straight lines with equal slopes.

Triangle waves contain only odd harmonics, but they are weaker and decrease faster than with a square wave. Like a sawtooth wave, the triangle has a reed-like quality, but it’s much thinner in its fundamental state.


I have covered the basic waveshapes, and it’s vital that you have some understanding of them. The best way to learn anything about music is to make it musical. So, I suggest you check out our article on the best free synth plugins, download one (or all), and start listening to the difference between waveshapes.

If you have a synth with more than one oscillator, you can combine them, either laying the same waveshapes or merging different shapes for interesting textures. As you progress, you’ll find lots of other options, like changing the pitch or syncing oscillators, but for now, let’s stick to the basics.

Filters

A filter or VCF (Voltage Controlled Filter) removes certain frequencies from a sound. When you hear people talk about synths and creating sounds, they often mention the cutoff or cutoff frequency. All that means is the frequency where the filter comes into effect, and you can adjust the cutoff as you like.

The cutoff isn’t something that you need to set in stone until you are done with a particular sound, it’s a tool that can be re-adjusted on the fly during a performance to create changes to your tone.

Some synths allow you to switch between different filter types, so here are the most common types:

High-pass filter

A high-pass filter allows frequencies greater than the cutoff frequency to pass through untouched. Any frequency below the cutoff frequency is attenuated, cut, or sometimes referred to as rolled off.

Low-pass filter

It’s the opposite of a high-pass filter. Any frequencies below the cutoff frequency will pass through untouched. Anything above the cutoff frequency will be rolled off.

Bandpass filter

If you think about any transmission or signal, it has a specific bandwidth: a lowest and highest point. A bandpass filter creates a new bandwidth so that only frequencies within the allocated band are allowed to pass.

Notch filter

A notch filter allows you to target very specific frequency ranges without altering everything else around it.

The other filters I have mentioned are, in different ways, attenuating the highest and/or lowest frequencies over the entire signal. Let’s say you want to remove everything between 1400 Hz and 1450 Hz, but keep everything below and above that short-range untouched; that’s what a notch filter can do.

Amplifier

An amplifier or VCA (Voltage Controlled Amplifier) is the easiest piece of the puzzle to understand. It boosts the signal to increase the volume and vice versa.

Envelope

An envelope, envelope generator, or contour generator is a modifier that helps shape the sound. The most common type of envelope is an ADSR envelope. That stands for attack, decay, sustain, and release.

The attack is how quickly a sound reaches full volume. Decay refers to how long it takes the maximum volume to drop to the volume level set by the sustain.

When you think of sustain, you think of a note being sustained by a pedal. In this context, it refers to the volume level of a sound while a note is held. The release is how quickly the volume returns to zero after the note has been released.

Envelopes are one of the most important areas of a synth when it comes to sound design. Synths can have one or more, and envelopes can often work in conjunction with the filter cutoff.

For example, the filter may allow you to adjust the envelope amount, which means the cutoff frequency determines the amount of the envelope settings applied to the sound.

LFO

A low-frequency oscillator (LFO) isn’t a sound generator like the oscillators described above. Instead, it can affect the sound using a frequency typically under 20 Hz.

You may already know that the human hearing range is 20 Hz to 20 kHz, so how does a frequency you can’t hear alter the sound? Well, it’s used to oscillate different parts of the sound to create movement.

For example, if applied to the filter cutoff, the LFO can create filter sweeps by oscillating the cutoff frequency. Alternatively, if applied to the amplifier, it can create a vibrato effect by oscillating the amplitude.

Arpeggiator

You may already be familiar with an arpeggiator because they are included in lots of beginner keyboards, too. An arpeggiator creates a repeating sequence of notes, in which you can control the notes used, the pitch, and the tempo.

Most arpeggiators offer various playback patterns, like forward, backward, random, etc.

Signal path

The journey that the electrical signal takes from creation to end sound is called the signal path. Some synths have a predetermined signal path, and some allow you to dictate the signal path. The benefit of altering the signal path is that you get greater control of your final sound.

In basic terms, you can think of it like a guitarist’s pedalboard: the guitar plugs into the pedalboard, and the signal passes through selected pedals before reaching the amp. You’ll see guitarists use footswitches to activate or bypass individual pedals/effects, depending on the sound required.

Each phase of a synth’s signal path plays a part in shaping the output. Rather than begin with anything too complicated, let’s start with the most simple fixed signal path. Starting with the basics of generating and outputting noise in subtractive synthesis, it looks like this:

Oscillator to Filter to Amplifier – then out to your speakers.

Other contributors like LFOs and envelopes are known as modifiers or modulation sources. Modulation sources will fit into your signal path wherever you have assigned them.

Note: What you need to remember is that the core of your signal path is tone generation (oscillator), then EQ (filter), then amplification.

How to use a synthesizer?

Unlike learning to a traditional instrument, there aren’t many set guidelines to follow when it comes to synths. Synthesizers encourage experimentation, and as I said earlier, the best way to learn is to make it musical. So, don’t forget to download some of the awesome free synth plugins that we recommended.

Rather than tell you exactly how to use a synth and list an impossible number of options, I will highlight a couple of things you should avoid.

When you create a sound that you like through adjusting the oscillators, filter, envelope settings, and so on, it’s what we call a patch. Many synths will allow you to save your favorite patches as user presets so that they are easy to recall. Although, with all those knobs and sliders at your disposal, it’s easy for things to go very wrong, very fast.

If you’re using a synth like a Nord Electro with some stunning preset patches, it’s easy to find your way back to the preset sound if your tweaking doesn’t go well. On the other hand, if you are using something like a Moog Grandmother, with no presets, it’s much easier to get lost and not find your way home.

It might not be an issue at home, but if you are in a band and want to introduce a synth to your live shows, you have to be careful. So, if you are a synthesizer beginner and want to use one on stage, it might be a good idea to start with something that offers preset patches. For everything else, you should learn at home before taking it on stage.

You can make very subtle or very dramatic changes to your sound with small adjustments; make sure it’s the right kind of drama and not the kind that gets you kicked out of the band.

If you’re still in search of your very first synths, make sure to check out my recent article discussing the best synthesizers for every budget; I cover over 15 awesome units there.

Different types of synthesizers

Synthesizers come in all shapes and sizes, and there are multiple types of synthesis to consider. But, before we get into different types of synthesis, let’s dismiss a common newbie misconception.

It’s common to think of a synthesizer as a keyboard instrument because many come in that form. Having a musical keyboard does make synthesizers a little easier to understand, but they don’t all come in that form. Many synths are desktop units or rack-mount units with no keyboard.

Now is a good time to discuss control voltage (CV) briefly. CV or control voltage is something you will encounter in the synth world, and it’s the language that tells the synth what to do. It controls the different areas of a synth that, in turn, create audio.

If a synth has a keyboard or you connect a controller keyboard, pressing different keys will send different control-voltage values to the oscillator to determine the pitch produced. Without a keyboard, the underlying process is the same: the control voltage value you set via onboard controls will determine the pitch.

UDO synthesizers
UDO synthesizers | Image: Higher Hz

Before we move on, I should quickly touch on the terms gate and trig. You will see gate used often, and it’s what tells the synth when a note starts and ends. It’s as simple as thinking of a garden gate opening and closing.

With a keyboard, pressing and releasing a key will open and close the gate or start and end the note. Without a keyboard, a sequencer can generate gate signals to control the length of each note.

Like gate, trig (or trigger) is a signal, but instead of lasting for a set amount of time, it’s instantaneous. Because trigger signals are an instant pulse, they are more commonly used with drum synths and other such sounds rather than melodic sounds.

Here are the main types of synthesis to get familiar with:

Subtractive synthesis

This type of synthesis is the most common, and it’s what much of the info above comes from. The name comes from the process of generating a raw tone then removing frequencies via the filter.

Subtractive synthesis is extremely versatile because of the number of modulation options.

Additive synthesis

Instead of subtracting from the waveshapes, additive synthesis adds waveshapes together to build sounds.

FM synthesis

FM stands for frequency modulation. Instead of oscillators, it uses operators to generate signals. An operator will generate a core signal, and another operator will modify that core signal.

There can be two operators or more; the more you have, the more complex sounds you can create. Other modulation sources like envelopes are available, too.

Granular synthesis

Granular synthesis can be difficult to grasp, so I will keep this short and basic. It is sample-based, and rather than triggering a full sample, it triggers small grains of the sample that play in a loop. It can generate unexpected results, and it’s great for making interesting textures.

Modular synthesizers

Modular synths are expansive and are built by connecting modules together. The ability to combine individual modules means you can literally build your dream synth setup.

modular synth setup
Instruo modular setup | Image: Higher Hz

Semi-modular synths are also available, which offers both a set signal path and the option to patch in other modules. However, the modules are fixed in one location.

Analog or digital?

Analog versus digital is an argument that often arises amongst synth fans. The truth is, whatever your preference, both have their place.

The difference is that analog uses VCOs, sound-generating circuits, and modulators. Digital synths use numerically-controlled oscillators and function more clinically, as you’d expect from a computer.

Analog synths often sound warmer, and at times less consistent, which is part of their charm. As analog synths came first, that’s the basis I use for my examples throughout this article.

Why should I use a synthesizer?

The simple answer is that synthesizers create sounds that you can’t with other instruments. Whether it’s bass sounds, leads, pads, or percussion, synths can do it all. They are invaluable in the studio or on the stage and will change how you approach making music.

using synthesizers on stage
Synthesizers used in a live setting

Using presets is absolutely fine, but one of the main reasons to use a synth is for the vast sound design potential. Having the ability to create unique patches is something that many musicians take great satisfaction from.

What kind of music uses synthesizers?

There aren’t many genres that haven’t made use of synthesizers in some way. But, it’s safe to say electronic music is where they are most prominent. That means genres like EDM, techno, house, trap, dubstep, etc.

But, before those genres were around, synths played a huge part in the history of funk, fusion, jazz, rock, hip-hop, and more.

Conclusion

Synthesizers are in a world of their own. You can learn a little and have fun or learn a lot, and it will be a life-long journey. Now that you’ve taken that first step don’t look back!

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