Music That's Never the Same Twice

The background music isn’t a recording. There’s no audio file. It’s synthesised as the game runs — notes chosen and sounded on the fly — so it never loops and it’s a little different every time. For an ambient world you wander through indefinitely, that suits it better than a track that repeats every two minutes.

Why it can’t sound wrong

The notes are drawn from a major pentatonic scale. A regular scale has seven notes; a pentatonic scale uses five, and the two that are left out are the ones most likely to clash. The practical upshot is that any combination of pentatonic notes sounds at least fine together. You can play them in any order, overlap them, land on any one — it stays consonant.

This is a well-known party trick: the black keys on a piano form a pentatonic scale, and you can mash them at random and it still sounds vaguely pleasant. That property is exactly what you want when a program is choosing notes with no composer checking them. The generator picks notes essentially at random from the scale, and the scale guarantees the result is harmonious.

# C major pentatonic across three octaves; pick from these at random
var base := [261.63, 293.66, 329.63, 392.00, 440.00]   # C D E G A

Making a note sound like a note

A raw sine wave is a dull electronic beep. A couple of touches make it a soft bell instead.

• Shape over time (the envelope). A real struck note starts quickly and fades away slowly. Each note is given a soft attack and a long, decaying tail rather than switching on and off abruptly.
• A harmonic. Adding a quieter copy of the note an octave up gives it a bell-like timbre instead of a pure tone.

var env := (1.0 - exp(-t * 18.0)) * exp(-t * decay)   # quick in, slow fade
var tone := sin(TAU * f * t) + 0.35 * sin(TAU * f * 2.0 * t)  # + octave = bell

Underneath the bell notes sits a very quiet drone — a sustained low root and fifth — which gives the whole thing a warm floor to rest on. Everything is run through a reverb effect so the notes sound like they’re in a space rather than right against your ear.

Reacting to the time of day

The music shifts with the world. There’s a single “calm” value tied to the time of day — covered in the lighting post — and at night the generator leaves longer gaps between notes and favours the lower octaves. So the music thins out and settles as it gets dark, matching the mood the lights and sky are setting.

That’s the whole system: random notes from a scale that can’t clash, shaped into soft bells over a drone, easing with the time of day. Simple ingredients, and because nothing is pre-recorded, you never hear the same minute twice.

The last two posts step back from individual systems — first the design rule behind all of them, then what it’s like to actually walk through the result in VR.