# Engine sound — provenance

`truck-loop.mp3` is the truck engine you hear while driving (`src/engine/world/DriverWorld.js`
`ENGINE_LOOP` → `EngineAudio`'s load loop).

| File | Source | Author | Licence | What it is |
|---|---|---|---|---|
| `truck-loop.mp3` | [536960 — "TRUCK (PASSING) – 2"](https://freesound.org/people/SamuelGremaud/sounds/536960/) | SamuelGremaud | [CC0 1.0](https://creativecommons.org/publicdomain/zero/1.0/) | A truck passing slowly in a traffic jam on the French A7 (ZOOM H4n Pro) |

Licence checked on the sound's Freesound page on 2026-10-02 (Gyan found it as Pixabay's re-upload,
"truck-passing-2-27104"; the CC0 original is the source we credit).

**Edits made** (`sox` + `lame`): the close pass cut out (21.5–29.5 s), downmixed to mono at
44.1 kHz, 96 kbps MP3. Nothing else — at runtime `synth.buildSeamlessLoop` evens its loudness and
crossfades the seam.

```
sox truck-passing-2.mp3 -c 1 -r 44100 cut.wav trim 21.5 =29.5
lame -b 96 -m m cut.wav truck-loop.mp3
```