FA-91558 / Digital signal filters / Member archive

Polyphase interpolator omits the L gain · case 03

The interpolated signal is L times too quiet because zero-stuffing removed energy.

Member previewVariant 3 · 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 3	`[-6, 0, 0, 0, -6, 0, 0, 0, -12, 0, 0, 0, 9, 0, 0, 0, 6, 0, 0, 0]`	`[-24, 0, 0, 0, -24, 0, 0, 0, -48, 0, 0, 0, 36, 0, 0, 0, 24, 0, 0, 0]`	Failed

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