How GPS becomes engine sound

EV·ENGINE turns GPS speed into engine sound. The browser reports how fast you are moving, the app derives acceleration from that, runs it through a virtual gearbox with real ratios, and synthesises an engine to match. There is no adapter, no wiring and no connection to the car.

Speed

The Geolocation API reports a position and, on most devices, a speed with it. Where the browser leaves speed empty, the app works it out from the distance between consecutive fixes. Both paths feed a smoother, because raw GPS speed steps and jitters in a way that would make the revs flutter.

Acceleration

Differentiate speed and you have acceleration, which stands in for throttle. Pull away hard and the engine loads up. Lift off and it drops onto the overrun, where the exhaust bangs.

The gearbox

Each machine carries a list of ratios in km/h per 1000 rpm, plus a shift point. Divide road speed by the current ratio and you have engine speed. Cross the shift point and the box changes up. Drop far enough below it and the box changes down.

The ratios are what make one machine feel unlike another. The GT V12 runs eight of them and shifts at 3,800 rpm. The 2.0 TDI runs six and shifts at 2,300, because it redlines at 4,600 and revving it like a V12 would sound absurd.

The sound

Two engines sit behind one interface. Three machines play recordings: four looping files per car, on-load and off-load at low and high rpm, crossfaded by rpm and throttle and pitch-shifted to track engine speed.

The rest are synthesised live in an AudioWorklet. A pulse train fires once per cylinder event, an order bank adds the harmonic structure, then a sub oscillator, waveshaper saturation, filtered noise, comb resonators standing in for the exhaust pipe, a dynamic lowpass and a three-stage cabin EQ. Nothing is pre-recorded, so the note is exact at any rpm rather than stretched from the nearest sample.

Why there is no OBD adapter

A dongle in the OBD port would give real engine data, except an electric car has no engine to report. It would also mean hardware to buy, a pairing step, and a device left plugged into the car. GPS costs nothing and works in any car with a browser.

Curious what your own device reports? Signal Watcher shows GPS update rate and accuracy, audio latency, GPU, network and over 200 browser API checks. See also browser support for what the simulator needs.