Tutorials Audio

Synthesis Fundamentals: Oscillators, Filters, and Envelopes

Beginner · ~30 min

Overview

Every synthesizer, hardware or software, builds sound from the same handful of building blocks: an oscillator generates a raw tone, a filter shapes its frequency content, and an envelope controls how it changes over time. This guide explains each block in plain terms, using the site's own Synthetic Sound Generator as a live playground to hear each concept immediately.

What You Need

The site's Synthetic Sound Generator app open in another tab
Headphones or speakers to actually hear the differences described

Steps

Start with the oscillator's waveform

A sine wave is the purest, smoothest tone. A square wave sounds hollow and buzzy (rich in odd harmonics). A sawtooth sounds bright and aggressive (rich in all harmonics). The classic "synth bass/lead" starting point. Try switching waveforms in the generator and just listen to the character change.

Shape the tone with a filter

A low-pass filter removes high frequencies above a cutoff point, making a bright oscillator sound darker and warmer. Resonance boosts the frequencies right at the cutoff, adding an emphasised, sometimes squelchy character. This is the single biggest lever for a synth's overall tone.

Animate the sound with an envelope

An ADSR envelope (Attack, Decay, Sustain, Release) controls how volume (or filter cutoff) changes over the life of a note. A fast attack gives a percussive pluck, a slow attack gives a swelling pad. This is what makes a static tone feel like an instrument being played.

Add movement with an LFO

A Low-Frequency Oscillator modulates another parameter slowly and repeatedly, applied to pitch it's vibrato, applied to filter cutoff it's a rhythmic wobble, applied to volume it's tremolo. LFOs are what keep a sustained sound feeling alive rather than static.

Layer oscillators for richness

A single oscillator often sounds thin. Two oscillators slightly detuned from each other create the thick, "chorused" sound behind most classic synth basses and leads. Try this directly in the generator's multi-oscillator patches.

Pro Tips

Learn to identify these building blocks by ear in music you already like: most "how did they make that sound" questions resolve to a specific waveform, filter setting, or envelope shape.
Start every new patch from a single oscillator and basic envelope, then add filter movement and layering, building up from a simple base is far easier than starting complex and simplifying.
Small envelope changes have an outsized effect: before reaching for a different oscillator, try adjusting attack and release on what you already have.

Knowledge Base

Subtractive Synthesis in One Sentence

Subtractive synthesis starts with a harmonically rich raw waveform and removes (subtracts) frequencies with a filter to sculpt the final tone, as opposed to additive synthesis, which builds a sound up from individual sine waves. Nearly every classic analog and virtual-analog synth, and the site's own generator, works this way.

The Four Blocks, Restated Simply

Oscillator: What note and raw tone color.
Filter: How bright or dark, how sharp or smooth.
Envelope: How the sound starts, sustains, and ends.
LFO: How the sound moves and breathes over a held note.

Why This Matters Beyond Music

These same four building blocks are exactly what drive the site's Sound Design for Video and Ambient/Synthetic Sound Generators. A whoosh transition is really just a filtered noise oscillator with a fast envelope sweep. Understanding synthesis basics makes every other sound-design tool on this site far more controllable.

Where This Fits

This guide covers one specific part of audio recording. The wider picture, how microphone distance, room acoustics, polar patterns, and gain staging decide whether a recording is usable before any processing, is in Audio Recording Fundamentals: The Complete Guide, which frames the discipline as a whole and links out to the detailed guides underneath it, including this one. If you are starting from scratch rather than solving a specific problem, read that first and come back here.

FAQ

Q: Do I need to learn synthesis to use the Synthetic Sound Generator?
A: No. The presets work fine on their own. This tutorial is for anyone who wants to understand why the parameters do what they do, so tweaking feels intentional rather than random.

Q: What's the difference between subtractive and FM synthesis?
A: FM (frequency modulation) synthesis uses oscillators to modulate each other's pitch rapidly, creating complex, often metallic or bell-like tones that subtractive synthesis can't easily produce. A different, more advanced technique worth exploring once these fundamentals feel comfortable.