Codex
54 lines
2.4 KiB
JavaScript
54 lines
2.4 KiB
JavaScript
import { fftInPlace } from "./fft.js";
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import { TAU } from "./math.js";
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export function nextPowerOfTwo(value) {
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if (!Number.isFinite(value) || value < 1) throw new Error(`유효하지 않은 FFT 길이: ${value}`);
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let result = 1;
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while (result < value) result *= 2;
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return result;
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}
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export function prepareDelaySpectrum(samples, maximumDelaySamples = 0) {
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const fftSize = nextPowerOfTwo(samples.length + Math.ceil(maximumDelaySamples) + 2);
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const real = new Float64Array(fftSize);
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const imaginary = new Float64Array(fftSize);
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real.set(samples);
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fftInPlace(real, imaginary);
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return { real, imaginary, fftSize };
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}
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export function createDelayWorkspace(fftSize) {
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return { real: new Float64Array(fftSize), imaginary: new Float64Array(fftSize) };
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}
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export function addFrequencyDomainDelay(options) {
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const { output, spectrum, delaySamples, gain = 1, phaseOffsetDeg = 0, workspace } = options;
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if (!(delaySamples >= 0) || !Number.isFinite(delaySamples)) throw new Error(`유효하지 않은 delay: ${delaySamples}`);
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if (workspace.real.length !== spectrum.fftSize || workspace.imaginary.length !== spectrum.fftSize) {
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throw new Error("fractional-delay workspace 크기가 spectrum과 다릅니다.");
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}
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const size = spectrum.fftSize;
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const calibrationPhase = (phaseOffsetDeg * Math.PI) / 180;
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for (let bin = 0; bin < size; bin += 1) {
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const signedBin = bin <= size / 2 ? bin : bin - size;
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const phaseSign = signedBin === 0 ? 0 : signedBin > 0 ? 1 : -1;
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const phase = (-TAU * signedBin * delaySamples) / size + phaseSign * calibrationPhase;
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const phaseReal = Math.cos(phase);
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const phaseImaginary = Math.sin(phase);
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const inputReal = spectrum.real[bin];
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const inputImaginary = spectrum.imaginary[bin];
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workspace.real[bin] = inputReal * phaseReal - inputImaginary * phaseImaginary;
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workspace.imaginary[bin] = inputReal * phaseImaginary + inputImaginary * phaseReal;
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}
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// A real sequence has a real-valued Nyquist coefficient. Projecting this single self-conjugate
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// bin back to the real axis preserves Hermitian symmetry for fractional delays.
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workspace.imaginary[size / 2] = 0;
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fftInPlace(workspace.real, workspace.imaginary, true);
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const outputLength = Math.min(output.length, workspace.real.length);
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for (let sampleIndex = 0; sampleIndex < outputLength; sampleIndex += 1) {
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output[sampleIndex] += workspace.real[sampleIndex] * gain;
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}
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}
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