What is a synth and how does a synthesizer work?

What are these mysterious musi making devices that seem capable of making any sound and how do they even work? Analogue, digital, and everything in-between; we’re here to clear it up.

To some synthesizers are the holy grail of all things musical and represent an unlimited potential of aural soundscapes. To others they are the funny noise makers they find in their DAWs and can make it sound different by turning all the knobs with unknown terms like oscillator and LFO above the dials.

Whatever your knowledge, synth’s are great and in this article we’ll be exploring the most common questions about synthesizers with a glossary of terms at the end to help creators, enthusiasts, and outsiders alike to understand what these oft-confusing but impressive creations are and can do.

Synthesizer definition: What does synthesizer mean?

Synthesizer is named for pretty self-explanatory reasons: It’s a machine or software that is capable of synthesizing sounds using hardware, without the need for human input like plucking strings, blowing through pipes, or pressing down on keys – although often synthesizers utilise keyboards to make their audio signals playable by human hands.

A Synthesizer means an electronic musical instrument that creates its own audio signal to produce sounds.

What does a synthesizer do?

Synthesizer can be split into two primary categories: Analogue and digital. Whichever the type of synthesizer, it is doing essentially the same thing: producing audio signals. The variety of function and potential depends on what exactly the synth is offering in what it can do and how it can be used.

A synthesizer can do many things with its digital sound creation. It can be played like any other instrument, often using a keyboard that will either come built into it or – as is common these days with software synths – MIDI keyboards which can be plugged in and used to control a synth.

Some synthesizers work as sequencers allowing users to program in patterns that the instrument will then play itself on loop. There are some hardcore sequencer synths out there that essentially provide the ability to create and produce an entire song that is playing itself on it’s own with poly loops.

Many synthesizers recreate the percussive elements of drum kits. These are usually lumped into their own category as drum machines and they can offer sampled hits rather than synthesis. Drum machines will often be used with a built-in sequencer function, like the famous Roland TR series which birthed the iconic 808.

Then there is the wacky world of modular synths. You may have seen images of rack synthesizers, modules with a sea of knobs lying underneath the shade of a web of coloured cables spreading out in an OCD nightmare tangle. Lets… not get into them right now, you can explore what the hell is going on there somewhere else if you want to know.

A modular eurorack synth
Image credit: Adi Goldstein

What is a synth keyboard?

A synth keyboard is probably what you’ve already wondered to yourself: a synthesizer module with a keyboard built into it making it completely playable using a recognisable method of music performance. These synths are popular because they allow for easy creation and allow people to play sounds back, making for quick feedback on how they’re editing the sound.

This is the most common type of synthesizer for casual enthusiasts and those who are just interesting in playing synthesized sounds without getting too technical into what they’re doing. That’s not to say that some of the most powerful and customisable synths don’t feature a keyboard too – some seriously big dogs do!

How a synthesizer works

No two synthesizers are completely alike and there are plenty of different methods that allow them to create audio through analogue and digital means. Strap in, as we’re about to cover the different forms of synthesis.

Subtractive synthesis: This uses complex waveforms which are generated by oscillators and shaped by filters which either boost or remove frequencies to tweak a final sound signal.

Additive synthesis: Additive uses a large number of waveforms and combines them into a cohesive sound. These are usually made up of sine waves.

Frequency modulation synthesis: Often acronymized into FM, this method modulates waveforms with the frequency of others. These waveforms can then be used to modulate other waveforms and so on the cycle goes.

Phase distortion synthesis: This is essentially a brand specific form of sound synthesis. Used by Casio for their CZ synthesizers, it works much the same as FM synthesis.

Wavetable synthesis: These synthesizers modulate between digital representations of different waves to change their shape and timbre.

Sample-based synthesis: These use sampled recordings of sounds rather than generating their own. These can often be manipulated through the use of filters, envelopes, and LFOs.

Vector synthesis: This uses crossfading between different sound sources and was pioneers by the Prophet VS.

Granular synthesis: This splits audio samples into “grains” which are played back in a recombined state. It often splits its samples to between one hundredth and one tenth of a second in length.

Physical modelling synthesis: Taking a physical source of sound and making a mathematical model for it.

Synthesizer glossary: Glossary of synthesizer terms

ADSR: Attack, delay, sustain, and release. What are they? We’ll get to each of them individually below.

Amplitude: The volume of a tone of waveform, represented by the height of a waveform on an oscilloscope (click here in case you don’t know what that is too).

Analog: An analog circuit is an electronic system that uses a continuously variable signal. The term “analogue” describes the proportional relationship between a signal and a voltage or current that represents the signal.

Arpeggiator: Arpeggios are chords that are played in sequence, like strumming out each string on a guitar in sequence rather than one quick flourish. An arpeggiator simulates this movement of notes for you, sequencing a pattern of notes that make up a chord.

Attack: This is how long it takes for the sound to go from nothing to it’s peak. The longer the attack the more the sound will appear to glide in rather than start immediately.

Attenuator: A method of reducing the amplitude of an audio signal, essentially reducing its volume.

Band: A range of frequencies in an EQ.

Band Pass Filter: A filter that allows for only the band of frequencies surrounding the cutoff to pass through and prevents the frequencies outside of that band.

Bandwidth: This is the width of a band or the number of frequencies that are boosted or cut around a selected frequency.

Bank: No this isn’t a coin slot in your synth. This is where a group of patches are stored in MIDI instruments.

Bass: The bandwidth of low frequencies, usually accepted to be between 20Hz to 400 Hz.

Chorus: An effect which plays multiple copies of a signal, slightly out of time to create a new tone. Think about the difference between a solo singer and a choir of singers all singing the same note. This can also be called an Ensemble.

Clock: This creates a consistent timing that you can connect throughout the synths and other devices in your setup to keep them in sync.

Cutoff: This is controls the cutting off of frequencies, pretty simple huh? Acting as a filter this controls how much certain EQ frequencies are removed.

Controlled Voltage: Often presented as just CV. This can control any parameters in an analog synth. This is used to adjust the oscillators, filters, and envelopes.

Decay: This measures how long the tone will take to fall out after the sound has been triggered.

Delay: A copy of the signal which plays back after the original sound and varies in the time between repeating and how many times it will play back. It comes in many different forms, find out more here.

Digital: In synthesizers, this refers to a module that uses digital processors and uses the direct digital synthesis architecture. It uses a numerically-controlled oscillator. Erm, it’s basically a computer controlled sound.

Distortion: An effect which boosts the amplitude, often to a point of peaking that provides a crunching, crushing tone to the sound.

Dynamic: The range in volume of an audio signal.

Envelope: A filter that determines the tones of your synth sound. A standard envelope filter will use the ADSR setup to control the sound.

Equalisation: Usually referred to simply as EQ. This is used to control the frequencies in a sound.

Eurorack: A modular synthesizer format which has grown to become incredibly popular. They use compact, 3.5mm mono jacks and cables for patching signals. To find out more, head here.

Filter: Filters are what defines the shape of your synth sound by taking out specific harmonics.

Frequencies: This is the number of times a second that a sound wave will repeat its cycle. When this is increased it will provide a higher pitch to the human ear.

Gain: Another way of referring to the level of a signal.

Gate: These signals can turn notes on and off, change the stages of an envelope, or control when a sequence is started and stopped. This can also be used to refer to a dynamic effect that cuts off a sound below a certain level.

Harmonics: Overtone frequencies that are found at intervals equal to the fundamental frequency.

Low Frequency Oscillator: Usually referred to as an LFO, this is an oscillator moving so slowly it is below the audible range for the human ear. It is used to alter the movement of a sound by modulating the audible frequencies from its own range.

Low Pass Filter: A filter that lets frequencies below the cutoff to pass, eliminating high frequencies.

MIDI: Stands for Musical Instrument Digital Interface. Without getting into the technical complications of it, it is a system that allows control over digital synthesizers with a keyboard. You can find out more with our Introduction to MIDI here.

Modulation: This describes the changes in a signal. You can modulate most elements of an audio signal to define its output and how it travels.

Module: The units that make up modular synthesisers. These come in many forms… so many forms. You can find out more about what these modules can be and how they work here.

Noise: No we haven’t just added an obvious term here. In reference to synths, noise often refers to generators which add electrical noise to your signals. First found in analog synths, digital synths will sometimes simulate the effect but can’t replicate it authentically.

Octave: The intervals between a frequencies half or doubles, providing the same note but a different pitch.

Oscillator: These generate waveforms. Defining the shape of these waveforms has a huge impact on the sound you produce from a synthesiser.

Panning: The position of a signal on a stereo output in terms of left and right.

Patch: A pre-programmed sound that has been made up from oscillators/samples and customised then saved into a synthesizer. The name comes from the days of old when manually patching cables together created the desired sound.

Pitch: The frequency of a soundwave. The higher the frequency the higher the pitch of the sound will be to the ear.

Polyphony: The number of voices that a synth can play at a time. A monophonic synth can play only one voice, a paraphonic and duophonic synth both play 2 voices but work differently, and a polyphonic synth simply refers to multiple voiced synthesizers.

Portamento: This sweeps the pitch up or down between two notes when they’re played one after the other.

Pulse Width: This is the time a waveform will take to go from its highest point to its lowest point. The width refers to the visual length on the waveform of the signal.

Quantisation: This lines a signal up the closest increment in a specified range. Most commonly used when referring to rhythm and aligning notes up in time with a rhythmic grid.

Release: This defines the time taken for a sound to reach it’s lowest point in whatever the envelope is defining.

Resonance: Using feedback, this boosts the frequencies around the cutoff. This can emphasise harmonics and can generate a sine-wave if it is raised enough to boost the feedback.

Sample: A recorded sound bite which can be replayed and manipulated.

Sequencer: The arrangement of musical patterns which can be repeated to build up looping beats and melodies.

Sine Wave: The most straightforward waveform and the one you’re most likely to think of when you imagine an oscilloscope.

Square Wave: A waveform with very abrupt changes to its peak and trough, creating a shape with near right-angles.

Sustain: This describes how the sound will vary and sets the peak. For example, it will be the volume of the note when the attack reaches its destination.

Tempo: The speed at which music should be played defined by the number of beats in a minute.

Threshold: The level an effect must pass before it is activated.

Timbre: The character of a sound that isn’t related to its pitch or intensity. Can also be referred to as the tone clur or tone quality.

Treble: The bandwidth of high end frequencies. Commonly accepted as between 5.2kHz and 20kHz.

Tremolo: A modulation effect that impacts the volume.

Triangle Wave: Waveforms with a linear rise and fall giving it a triangular shape.

Trigger: The method uses to activate a module or synthesizer’s sound.

Velocity: Normally equating to the loudness of a note, this represents the dynamic attack of a trigger.

Vibrato: Effecting the pitch of a tone, this creates a funny warbling sound from a signal.

Voice: The sound created by an oscillator or a group of oscillators together.

Waveform: The visual display of a soundwave.

Writing about music, listening to music, and occasionally playing music.

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