Condition grade
Music is predictable over a few milliseconds. A click is not.
For every block of 2048 samples (about 43 ms at 48 kHz) vinyl-check fits an autoregressive model of order 32 and predicts each sample from the ones before it. What it cannot predict is the residual. In music it stays small and nearly white; a click stands out of it like a spike.
A sample becomes a candidate above 8 σ, with σ estimated robustly from the residual itself, so the threshold does not depend on level or loudness. A stripe check then removes drum hits: a click is a thin vertical line, at most 5 ms wide and 12 dB above its surroundings above 6 kHz.
- Pop loud enough to be heard through the music
- Click a single audible click
- Crackle barely audible alone, the crackle of a pause
The grade counts what you hear while the music plays.
Clicks per minute of music decide 90 % of the grade, pops 10 %: in loud music, most detected pops are instrument transients. Noise and clicks in pauses are reported, but they do not enter the grade. F is only given when the stylus skips. Mint is never given, because it needs a visual inspection.
Score0.9 × 88.2 + 0.1 × 87.1 = 88.1VG+ · 88