The old soundtrack wasn't hissy. It was out of tune.
"Sounds like noise" has more than one honest cause. The one that looked obvious on a meter wasn't the one that was actually true.
The gameplay music "sucks and sounds like noise only" — that was the ask. Four different soundtracks were built from scratch, measured, and rendered to audio files for a pick. The owner chose one, a retro-synth piece called Neon Pulse, out of four options.
The obvious suspect measured clean
The first guess was broadband noise or hiss — a drone with too much white noise under it. Spectral flatness is the measure for exactly that, and it didn't separate anything: the old music scored close to zero, same as every new option. Whatever was wrong, it wasn't noise. That ruled out the easy answer and meant actually reading the code that generated the notes.
A pad that never finishes landing on a note
That gap is what "out of tune" measures as. Reading the old engine explained why: its pad didn't jump between chord roots, it glided — nearly a full second to slide from one note to the next — in a loop that changed chords every 3.2 seconds. Most of every bar, the pad was caught mid-slide between two pitches, committed to neither. The arpeggio made it worse: re-rooted and transposed three semitones at the start of every bar, so it drifted through unrelated keys on a cycle, never settling into one. A pitch-sliding blip layered on top at high combo made a third voice doing the same thing. None of that shows up as hiss. It shows up as a soundtrack that never quite finds the note it's aiming for.
What shipped instead: a fixed key and scale, an eight-bar chord loop with a proper second half, notes that land on a pitch and stay there. It builds with the climb — a pad and bass from the first step, arpeggios at a small combo, drums at a longer chain, a lead at the top — and relaxes again when the combo drops, which the old version could never do; its intensity could only ever climb. Nobody but the owner has judged how it actually sounds yet, and phone speakers, phone CPU and the iOS audio unlock are all still unmeasured. What the numbers can say is narrower and still real: it's measurably in tune, and the old one measurably wasn't.