FA-91749 / Digital signal filters / Member archive

Feedback comb reads the most recently written slot · case 04

Echoes arrive after one sample regardless of D.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Input [D, g, samples]: y[n] = x[n] + g y[n-D] using a D-slot ring buffer with zero initial state; "bad-delay" if D < 1, "unstable" if |g| >= 1. Return exact fraction strings.

Why this case matters

Feedback combs build resonators and reverberators; ring-buffer indexing slips change the delay and the pitch.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression: random comb 8	`["1", "7/3", "-32/9", "37/27"]`	`["1", "3", "-2", "-1"]`	Failed

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