FA-91755 / Digital signal filters / Member archive

Feedback comb accepts unit feedback gain · case 05

g = 1 is accepted, giving a non-decaying (marginally stable) resonator instead of "unstable".

Member previewVariant 5 · 3 implementations · 6 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: unit gain rejected	`["1"]`	`"unstable"`	Failed

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