FA-91747 / Digital signal filters / Member archive

Feedback comb reads the most recently written slot · case 02

Echoes arrive after one sample regardless of D.

Member previewVariant 2 · 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 2	`["2", "2/3", "-13/9", "107/27", "-295/81", "1076/243", "-1423/729"]`	`["2", "2", "-1", "3", "-7/3", "2/3", "5/3"]`	Failed

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