57 lines
1.7 KiB
TypeScript
57 lines
1.7 KiB
TypeScript
import { nextPow2, realFftMagnitude } from "./yin.js";
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const A4_FREQ = 440;
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const A4_MIDI = 69;
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/**
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* Compute a 12-bin pitch-class chromagram for a single frame using the
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* vendored real FFT. Energy below 30 Hz or above the Nyquist is ignored.
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*/
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export function chromagramFromFrame(
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frame: Float32Array,
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sampleRate: number,
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minFreq = 30
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): Float32Array {
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const out = new Float32Array(12);
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if (frame.length < 8) return out;
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const mag = realFftMagnitude(frame);
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const fftSize = nextPow2(frame.length);
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const nyquist = sampleRate / 2;
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for (let k = 1; k < mag.length; k++) {
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const freq = (k * sampleRate) / fftSize;
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if (freq < minFreq || freq >= nyquist) continue;
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// k starts at 1 with sampleRate > 0, so freq > 0 and the log is finite.
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const midi = A4_MIDI + 12 * Math.log2(freq / A4_FREQ);
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const pc = ((Math.round(midi) % 12) + 12) % 12;
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const m = mag[k]!;
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out[pc] = out[pc]! + m;
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}
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return out;
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}
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/** Normalise a chromagram in-place so its max value is 1 (or zero remains zero). */
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export function normaliseChroma(chroma: Float32Array): Float32Array {
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let max = 0;
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for (let i = 0; i < chroma.length; i++) {
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const v = chroma[i]!;
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if (v > max) max = v;
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}
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if (max === 0) return chroma;
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for (let i = 0; i < chroma.length; i++) {
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chroma[i] = chroma[i]! / max;
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}
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return chroma;
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}
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/** Sum two same-length chromagrams in-place into `acc`. */
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export function accumulateChroma(
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acc: Float32Array,
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add: Float32Array
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): Float32Array {
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const len = Math.min(acc.length, add.length);
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for (let i = 0; i < len; i++) {
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acc[i] = acc[i]! + add[i]!;
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}
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return acc;
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}
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