Engine
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Run
Load changes the shape of each pulse, not just its level: a throttled cylinder pushes a softer, duller slug of gas into the pipe. Per-bank exhaust gives each bank its own pipe; merged puts every cylinder into one.
What you hear
The timing is the truth. The timbre is a model, and a small one. Each firing is a pressure slug into a pipe: a low thump plus a burst of filtered noise, shaped by load, sent through a quarter-wave resonator standing in for the exhaust pipe, then a soft saturation, then a muffler low-pass. No recording is involved anywhere.
Model details and known lies
Pulse. A sine that sweeps from about 140–180 Hz down to 45 Hz in 12 ms with an exponential decay (55 ms at no load, 30 ms at full), plus band-passed white noise centered 700–2500 Hz depending on load, decaying in 15–25 ms. Load raises amplitude, noise share and center frequency. Every pulse is one of four pre-rendered variants with a random ±3% rate and ±8% level, because real cycles differ slightly.
Pipe. A closed–open pipe of length L resonates at c/4L and odd multiples. Three band-pass filters at f, 3f and 5f (c = 450 m/s for hot exhaust gas) ring after each pulse. In per-bank mode each bank has its own pipe and the second pipe is 8% longer, as real headers never match; that mismatch, and the soft saturation after each pipe, is why a crossplane V8 burbles here in per-bank mode and stops when merged. In a purely linear model the two modes would be identical, which is the first known lie.
Not modeled. Intake noise, valvetrain, turbo, combustion chamber acoustics, pipe length per cylinder, the master-rod geometry of a radial, engine load on rpm (the rpm is whatever you set). Levels are normalized by cylinder count so a V12 is not twelve times louder than a single.