GPS Whistle

Whistle your location into any recording. It survives compression and can be decoded later.

Start your recorder, hold this device near it, turn the volume up, and press the button. It plays a soft chord, a short tune and a run of quick chords, twice: about 11 seconds, or 14 to 17 with an author name.

Location
How it works, and what it proves

The page encodes a 40-byte frame as a run of chords in G major: one chord of four notes for each byte, 48 thousandths of a second each. A tiny melody that spells G‑P‑S‑W in notes (G–B–E–B, by the French method Ravel and Debussy used to spell HAYDN) comes before the chords, and the same melody backwards comes after them. A decoder finds the chords by the melody, which also tells it how fast the recording is running. Reed–Solomon error correction and a CRC-32 check protect the frame. It carries the location on a ≈19 m grid (or snapped to a fixed ≈5 km grid in Coarse mode, or nothing in Off), the reported accuracy, a UUIDv7 (which includes the time), optionally 8 bytes of the current drand randomness beacon, and optionally an author name (up to 48 bytes of UTF-8, which lengthens the frame to 64 or 88 bytes and adds 1.5 to 3 seconds to each play). It plays twice.

In testing, it decoded through AAC, MP3 and Opus compression, generation loss, resampling down to 16 kHz, 8-bit audio, heavy noise, room reverb, clipping, automatic gain control, and recorders whose clocks run up to 4.5% fast or slow. In real rooms it has been read from a recorder 3 m from the speaker.