FA-91745 / Digital signal filters / Member archive

Feedback comb stores the input in its delay line · case 05

The impulse response has a single echo instead of a decaying train.

Member previewVariant 5 · 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 25	`["0", "-2", "4/3", "11/3", "1", "2", "-4/3", "-11/3"]`	`["0", "-2", "4/3", "31/9", "31/27", "193/81", "-293/243", "-2480/729"]`	Failed

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