Codex
63 lines
2.2 KiB
JavaScript
63 lines
2.2 KiB
JavaScript
import { dbToLinear } from "./math.js";
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export const MAX_FREQUENCY_RESPONSE_POINTS = 64;
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export const MAX_FREQUENCY_RESPONSE_HZ = 1_000_000;
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function phaseAt(point) {
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return point.phaseDeg ?? 0;
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}
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function wrapPhaseDeg(value) {
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const wrapped = ((value + 180) % 360 + 360) % 360 - 180;
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return Object.is(wrapped, -0) ? 0 : wrapped;
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}
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function writeResponse(output, gainDb, phaseDeg) {
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output.gainDb = gainDb;
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output.phaseDeg = wrapPhaseDeg(phaseDeg);
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output.linearGain = dbToLinear(gainDb);
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output.phaseRadians = (output.phaseDeg * Math.PI) / 180;
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return output;
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}
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/**
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* Piecewise-linear microphone response interpolation.
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*
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* Frequencies outside the measured curve use the nearest endpoint. Phase follows
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* the shortest wrapped path between points, avoiding a discontinuity at ±180°.
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* Passing an output object lets FFT loops reuse storage and avoid per-bin garbage.
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*/
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export function interpolateFrequencyResponse(points, frequencyHz, output = {}) {
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if (!Number.isFinite(frequencyHz) || frequencyHz < 0) {
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throw new RangeError(`frequencyHz must be a finite non-negative number: ${frequencyHz}`);
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}
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if (points === undefined || points === null || points.length === 0) {
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return writeResponse(output, 0, 0);
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}
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if (!Array.isArray(points)) throw new TypeError("frequency response points must be an array.");
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const first = points[0];
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const last = points[points.length - 1];
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if (frequencyHz <= first.frequencyHz) {
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return writeResponse(output, first.gainDb, phaseAt(first));
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}
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if (frequencyHz >= last.frequencyHz) {
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return writeResponse(output, last.gainDb, phaseAt(last));
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}
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let low = 0;
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let high = points.length - 1;
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while (high - low > 1) {
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const middle = Math.floor((low + high) / 2);
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if (frequencyHz < points[middle].frequencyHz) high = middle;
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else low = middle;
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}
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const left = points[low];
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const right = points[high];
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const ratio = (frequencyHz - left.frequencyHz) / (right.frequencyHz - left.frequencyHz);
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const gainDb = left.gainDb + (right.gainDb - left.gainDb) * ratio;
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const leftPhase = phaseAt(left);
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const phaseDelta = wrapPhaseDeg(phaseAt(right) - leftPhase);
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return writeResponse(output, gainDb, leftPhase + phaseDelta * ratio);
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}
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