What is a Synthesizer? A Beginner's Guide

A synthesizer is an electronic instrument that generates sound from scratch using electrical signals. Unlike a piano or guitar, which produce sound by vibrating physical strings, a synthesizer builds sound mathematically — giving you total control over every aspect of the tone you hear.

That might sound technical, but the core idea is simple: you tell the synth what kind of sound to make, and it makes it. From the warm bass of classic 80s pop to the sharp leads of modern electronic music, virtually every electronic sound you've ever heard was made by a synthesizer.

A Brief History

Synthesizers have been around longer than most people realise. The Moog synthesizer, developed by Robert Moog in the 1960s, was one of the first widely used instruments of its kind. It was famously used on Wendy Carlos's 1968 album Switched-On Bach, which showed the world that electronic instruments could rival acoustic ones.

Through the 70s and 80s, synths became central to pop, rock, and electronic music. Bands like Kraftwerk, Depeche Mode, and New Order built entire sounds around them. Today, synthesizers are everywhere — in your favourite songs, film scores, and video games — and thanks to the web, you can play one right now without buying a single piece of hardware.

How Does a Synthesizer Work?

Every synthesizer, whether it costs £50 or £5,000, is built around the same basic building blocks: oscillators, filters, and envelopes. Understanding these three things will give you a solid mental model for any synth you ever use.

Oscillators — The Sound Source

An oscillator generates a raw waveform — a continuously repeating electrical signal. The shape of that waveform determines the basic character of the sound:

• Sine wave — smooth and pure, like a flute or whistle. Contains only the fundamental frequency, no overtones.
• Square wave — hollow and buzzy, like an old video game. Rich in odd harmonics.
• Sawtooth wave — bright and cutting, like a string section or lead synth. Contains all harmonics.
• Triangle wave — softer than square, more mellow. Good for bass and pads.

Many synthesizers layer two or more oscillators slightly out of tune with each other — this is called detune — to create a thicker, richer sound. You can try this yourself in Synthio using the Detune slider.

Filters — Shaping the Tone

A raw oscillator waveform sounds quite harsh on its own. The filter is what sculpts that raw sound into something musical. The most common type is a lowpass filter, which cuts out high frequencies above a set point (the cutoff frequency) and lets the low frequencies through.

Turn the cutoff down and the sound gets darker and more muffled — like hearing music through a wall. Turn it up and the sound becomes brighter and more present. The resonance control adds a peak at the cutoff frequency, giving the filter a sharp, characteristic sound often described as "wah" or "squelchy."

Envelopes (ADSR) — Controlling Sound Over Time

An oscillator runs continuously, but notes don't sustain forever — they have a shape over time. That's what an envelope controls. The standard envelope has four stages, known as ADSR:

• Attack — how long it takes for the sound to reach full volume after a key is pressed
• Decay — how quickly it falls from peak to the sustain level
• Sustain — the volume level held while the key stays pressed
• Release — how long the sound fades after the key is released

A short attack and short release gives you a punchy, percussive sound. A long attack and long release creates a smooth, pad-like swell. ADSR is one of the most powerful tools in sound design — we go deep on it in a dedicated article.

Effects — Adding Space and Character

On top of the core signal chain, synthesizers typically include effects like reverb (adding a sense of physical space), delay (echo), and chorus. These turn a dry, clinical sound into something with depth and atmosphere. Even a small amount of reverb can make a synth sound dramatically more musical.

Types of Synthesizers

There are several approaches to synthesis, each with a different character:

• Subtractive synthesis — starts with a harmonically rich waveform and uses filters to subtract frequencies. The most common type, used in classic Moogs and most modern software synths.
• FM synthesis — one oscillator modulates the frequency of another, creating complex metallic and bell-like tones. Famous in the Yamaha DX7.
• Wavetable synthesis — cycles through stored waveform snapshots to create evolving, animated sounds. Popular in modern synths like Serum.
• Sample-based synthesis — uses recordings of real instruments (piano, strings, etc.) as the sound source. Gives you acoustic realism with electronic control.

Synthio uses both subtractive synthesis (for the Synth preset) and sample-based synthesis (for Grand Piano, Rhodes, Wurlitzer, and Organ) — giving you the best of both worlds in one place.

Why Play a Synthesizer Online?

Hardware synthesizers are incredible — but they're expensive, bulky, and require setup. A good software synth plugin can cost hundreds of euros and needs a DAW to run. Playing a synthesizer in your browser changes all of that.

With Synthio, you get a fully functional synthesizer with ADSR envelope, filter, reverb, detune, and multiple waveforms — all free, right in your browser, on any device. No downloads, no plugins, no account required. You can connect a real MIDI keyboard and play it just like a hardware instrument, or tap the keys on your phone.

It's the fastest way to explore synthesis, practice music, or just make some noise.