Four real idle recordings. Pick one and listen while stopped. It applies to both A and B.
Records motion, GPS speed and the engine model at 25 Hz. GPS position is not recorded.
A: loop bank. Constant-RPM loops cut from the recordings for every 200–300 rpm, on- and off-throttle. They're phase-aligned and crossfaded by RPM and throttle. This is the classic racing-game approach: steady and smooth.
B: granular replay. Plays the actual recordings continuously, choosing each engine cycle from the moment where the real car was at the same RPM and load. When your driving matches the recording, you hear it untouched, gear changes and all.
Recordings: Ford Mustang GT500 by VacekH on Freesound (CC0). RPM was measured from the firing-order harmonics.
Idle recordings (Freesound): 1985 Ford Mustang 5.0 by lmbubec (CC0); Chevrolet Corvette by kyles (CC0); 1964 Chrysler Windsor by lonemonk (CC BY 4.0); GT500 by VacekH (CC0).
Gearing: S550 Mustang GT. 10R80 ratios from Ford's chart, MT82 manual ratios from CJ Pony Parts, 255/40R19 tyres.
Keep the screen on with the app open. iOS stops web audio and sensors when the screen locks.