FA-91569 / Digital signal filters / Member archive

Polyphase interpolator drops trailing taps of shorter phases · case 04

When the filter length is not a multiple of L the last taps are never applied.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Input [h, L, samples] (integers). Zero-stuff by L and filter with h, scaled by gain L: y[mL + p] = L sum_j h[jL + p] x[m - j]; return len(samples) * L outputs in time order.

Why this case matters

Interpolators feed DACs and sample-rate converters; gain and phase-indexing slips cause level errors and imaging.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression: random interpolator 18	`[16, 8, 4, -6, -16, -2, -24, -10, -24, -2]`	`[16, 8, 4, -6, -32, -2, -12, -10, -20, -2]`	Failed

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