FA-91450 / Digital signal filters / Member archive

CIC comb subtracts the new sample from the delayed one · case 05

Outputs have the opposite sign for odd N.

Member previewVariant 5 · 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 10	`["3/64", "7/64", "-1/64"]`	`["-3/64", "-7/64", "1/64"]`	Failed

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