FA-91439 / Digital signal filters / Member archive

CIC combs ignore the differential delay · case 04

With M = 2 the comb subtracts the previous low-rate sample instead of the one two samples back.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Input [N, R, M, samples]: N integrator stages at the input rate, keep the integrator output at indices R-1, 2R-1, ... (whole blocks only), then N comb stages y = v - v[k-M] at the low rate with zero initial state; divide by the gain (R M)^N and return exact fraction strings.

Why this case matters

CIC decimators front most digital down-converters; decimation phase, delay or gain slips distort the passband level.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression: random cic 13	`["1/4", "1/4", "5/12"]`	`["1/4", "3/4", "7/6"]`	Failed

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