Lucas WintherandClaude Opus 5.5
e5773e0c33
2:1 decimation (44.1k -> 22.05k, used to render the warped MIDI for the alignment page) recomputed 65 windowed-sinc taps per output sample: ~17 s for a 4.7 min stereo render. Outputs at integer input positions now reuse one tap table; arithmetic is identical, so results are bit-identical. Co-Authored-By: Claude Opus 5.5 <[email protected]>
40 lines
1.8 KiB
TypeScript
40 lines
1.8 KiB
TypeScript
import { test, expect } from "bun:test";
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import { resample } from "../../src/dsp/resample.ts";
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// Reference: the direct windowed-sinc evaluation (the original implementation), used to check the cached path is exact.
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function reference(x: Float32Array, from: number, to: number): Float32Array {
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const sinc = (v: number) => (v === 0 ? 1 : Math.sin(Math.PI * v) / (Math.PI * v));
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const ratio = to / from, outLen = Math.round(x.length * ratio), out = new Float32Array(outLen);
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const cutoff = Math.min(1, ratio), half = 16 / cutoff;
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for (let j = 0; j < outLen; j++) {
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const t = j / ratio;
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const lo = Math.max(0, Math.ceil(t - half)), hi = Math.min(x.length - 1, Math.floor(t + half));
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let acc = 0, wsum = 0;
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for (let i = lo; i <= hi; i++) {
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const d = i - t;
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const w = 0.42 + 0.5 * Math.cos((Math.PI * d) / half) + 0.08 * Math.cos((2 * Math.PI * d) / half);
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const k = cutoff * sinc(cutoff * d) * w;
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acc += x[i]! * k; wsum += k;
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}
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out[j] = wsum !== 0 ? acc / wsum : 0;
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}
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return out;
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}
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const noise = (n: number) => { let s = 1; return Float32Array.from({ length: n }, () => ((s = (s * 16807) % 2147483647) / 2147483647) * 2 - 1); };
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test("2:1 decimation is bit-identical to the direct evaluation and fast", () => {
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const x = noise(44100);
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expect(Array.from(resample(x, 44100, 22050))).toEqual(Array.from(reference(x, 44100, 22050)));
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const big = noise(44100 * 60);
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const t0 = performance.now();
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resample(big, 44100, 22050);
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expect(performance.now() - t0).toBeLessThan(500); // one minute of audio: ~50 ms cached vs ~1.7 s direct
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});
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test("non-integer ratios are unchanged", () => {
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const x = noise(4800);
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expect(Array.from(resample(x, 48000, 44100))).toEqual(Array.from(reference(x, 48000, 44100)));
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expect(Array.from(resample(x, 22050, 44100))).toEqual(Array.from(reference(x, 22050, 44100)));
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});
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