The case says 96 kHz.
Recording sound means taking snapshots of it: 96,000 every second here. Two snapshots catch one cycle of a sound wave, so the highest pitch the disc can hold is half that: 48 kHz. The canvas below is that promise.
A real disc can fill it.
The app reads the disc and draws every frequency it finds. This one carries all the way up. Plenty of honest masters stop lower, and that on its own proves nothing.
This one goes silent at 24.8.
The energy stops dead, and above the line there is nothing at all. Not faint, not quiet: nothing. A real master leaves its own noise up there.
Bigger file. Zero new detail.
Someone stretched a CD-sized master into a hi-res container. A CD tops out at 22.05 kHz. This disc goes quiet a touch above it, where CD-grade material lands. Enlarge its spectrogram: bigger blocks, nothing new.
The silence is the fingerprint.
Side by side, there’s no mistaking it. It is the empty band that gives a disc away, never the height of the line alone. 19 of 103 discs measured so far were caught, by this or by one of the other tests: a hole punched in the spectrum, dither standing in for music, or an SACD landing at CD height. Every one is named below.