FA-91685 / Digital signal filters / Member archive

Resampling plan swaps the interpolation and decimation factors · case 05

48 kHz to 44.1 kHz is planned as up 160, down 147 instead of up 147, down 160.

Member previewVariant 5 · 3 implementations · 7 checks per implementation

Case contract

Input [fin, fout, rolloff] (positive integer rates, rolloff in (0, 1]). Reduce fout/fin to up/down = L/M by gcd, intermediate rate = fin L, anti-alias cutoff = min(fin, fout)/2 * rolloff in Hz and normalized to the intermediate Nyquist. Return {"up", "down", "intermediate_rate", "cutoff_hz", "cutoff_norm"} or "bad-spec".

Why this case matters

Sample-rate converters are planned from these numbers; a wrong cutoff reference aliases or dulls the output.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression: 48k to 44.1k	`{"cutoff_hz": "19845", "cutoff_norm": "1323/256000", "down": 147, "intermediate_rate": 7680000, "up": 160}`	`{"cutoff_hz": "19845", "cutoff_norm": "9/1600", "down": 160, "intermediate_rate": 7056000, "up": 147}`	Failed

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