Initial Commit

packages/media/audio/audio-analysis-pitch/src/algorithms/chromagram.ts

@@ -0,0 +1,56 @@
+import { nextPow2, realFftMagnitude } from "./yin.js";
+
+const A4_FREQ = 440;
+const A4_MIDI = 69;
+
+/**
+ * Compute a 12-bin pitch-class chromagram for a single frame using the
+ * vendored real FFT. Energy below 30 Hz or above the Nyquist is ignored.
+ */
+export function chromagramFromFrame(
+    frame: Float32Array,
+    sampleRate: number,
+    minFreq = 30
+): Float32Array {
+    const out = new Float32Array(12);
+    if (frame.length < 8) return out;
+    const mag = realFftMagnitude(frame);
+    const fftSize = nextPow2(frame.length);
+    const nyquist = sampleRate / 2;
+    for (let k = 1; k < mag.length; k++) {
+        const freq = (k * sampleRate) / fftSize;
+        if (freq < minFreq || freq >= nyquist) continue;
+        // k starts at 1 with sampleRate > 0, so freq > 0 and the log is finite.
+        const midi = A4_MIDI + 12 * Math.log2(freq / A4_FREQ);
+        const pc = ((Math.round(midi) % 12) + 12) % 12;
+        const m = mag[k]!;
+        out[pc] = out[pc]! + m;
+    }
+    return out;
+}
+
+/** Normalise a chromagram in-place so its max value is 1 (or zero remains zero). */
+export function normaliseChroma(chroma: Float32Array): Float32Array {
+    let max = 0;
+    for (let i = 0; i < chroma.length; i++) {
+        const v = chroma[i]!;
+        if (v > max) max = v;
+    }
+    if (max === 0) return chroma;
+    for (let i = 0; i < chroma.length; i++) {
+        chroma[i] = chroma[i]! / max;
+    }
+    return chroma;
+}
+
+/** Sum two same-length chromagrams in-place into `acc`. */
+export function accumulateChroma(
+    acc: Float32Array,
+    add: Float32Array
+): Float32Array {
+    const len = Math.min(acc.length, add.length);
+    for (let i = 0; i < len; i++) {
+        acc[i] = acc[i]! + add[i]!;
+    }
+    return acc;
+}