Was it FCC noise floor concerns or receiver IF behavior that pushed the US to 75 microseconds instead of 50? I’m bench-tuning an Orban 8100A today and that 2.1 kHz turnover (19 kHz pilot, 38 kHz L-R) really shifts sibilance control; I tame it with a light HF shelf before the clipper, but I’d love the true origin story…
Mostly receiver noise — 75 µs was picked in the mono era to beat the FM detector’s ‘triangular noise’, then the 1961 stereo pilot system just kept it for compatibility. With that 2.1 kHz knee on an 8100A, a tiny HF shelf before the clipper plus strict pilot-protect is right; try a bench A/B of 50 vs 75 µs and you’ll see less hiss but more sibilant overshoot at 75 µs (background: FM broadcasting - Wikipedia).