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/**
* Simple Audio Analyzer - Lightweight BPM and Key Detection
* Based on proven open-source algorithms - minimal CPU usage
*
* Features:
* - Simple peak detection for BPM (fast, accurate)
* - Basic chroma analysis for key (lightweight)
* - Analyzes only 10 seconds (very fast)
* - Processes in chunks to prevent blocking
* - No heavy FFT or autocorrelation loops
*
* @author SoundStudioPro
*/
class SimpleAudioAnalyzer {
constructor() {
this.audioContext = null;
this.isAnalyzing = false;
// Camelot wheel mapping
this.camelotWheel = {
'A♭ minor': '1A', 'G# minor': '1A', 'Ab minor': '1A',
'B major': '1B',
'E♭ minor': '2A', 'D# minor': '2A', 'Eb minor': '2A',
'F# major': '2B', 'Gb major': '2B',
'B♭ minor': '3A', 'A# minor': '3A', 'Bb minor': '3A',
'D♭ major': '3B', 'Db major': '3B', 'C# major': '3B',
'F minor': '4A',
'A♭ major': '4B', 'Ab major': '4B', 'G# major': '4B',
'C minor': '5A',
'E♭ major': '5B', 'Eb major': '5B', 'D# major': '5B',
'G minor': '6A',
'B♭ major': '6B', 'Bb major': '6B', 'A# major': '6B',
'D minor': '7A',
'F major': '7B',
'A minor': '8A',
'C major': '8B',
'E minor': '9A',
'G major': '9B',
'B minor': '10A',
'D major': '10B',
'F# minor': '11A', 'Gb minor': '11A',
'A major': '11B',
'D♭ minor': '12A', 'C# minor': '12A', 'Db minor': '12A',
'E major': '12B'
};
// Simple key profiles (Temperley - lightweight)
this.majorProfile = [5.0, 2.0, 3.5, 2.0, 4.5, 4.0, 2.0, 4.5, 2.0, 3.5, 1.5, 4.0];
this.minorProfile = [5.0, 2.0, 3.0, 4.5, 2.0, 4.0, 2.0, 4.5, 3.5, 2.0, 3.5, 4.0];
this.noteNames = ['C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#', 'A', 'A#', 'B'];
}
initAudioContext() {
if (!this.audioContext) {
this.audioContext = new (window.AudioContext || window.webkitAudioContext)();
}
return this.audioContext;
}
/**
* Main analysis - simple and fast
*/
async analyzeAudio(audioUrl, progressCallback = null) {
if (this.isAnalyzing) {
throw new Error('Analysis already in progress');
}
this.isAnalyzing = true;
try {
if (progressCallback) progressCallback('loading', 10);
const ctx = this.initAudioContext();
const response = await fetch(audioUrl);
if (!response.ok) throw new Error(`Failed to fetch: ${response.status}`);
if (progressCallback) progressCallback('decoding', 30);
const arrayBuffer = await response.arrayBuffer();
const audioBuffer = await ctx.decodeAudioData(arrayBuffer);
// Get first channel only (mono)
const samples = audioBuffer.getChannelData(0);
const sampleRate = audioBuffer.sampleRate;
// Analyze only first 10 seconds (very fast)
const maxSamples = Math.min(samples.length, sampleRate * 10);
const analysisSamples = samples.slice(0, maxSamples);
if (progressCallback) progressCallback('detecting_bpm', 50);
// Simple BPM detection
const bpm = await this.detectBPM(analysisSamples, sampleRate, progressCallback);
if (progressCallback) progressCallback('detecting_key', 80);
// Simple key detection
const keyInfo = await this.detectKey(analysisSamples, sampleRate, progressCallback);
if (progressCallback) progressCallback('complete', 100);
return {
bpm: Math.round(bpm * 10) / 10,
key: keyInfo.key,
camelot: keyInfo.camelot,
energy: 'Medium',
confidence: Math.round(keyInfo.confidence)
};
} catch (error) {
console.error('Analysis error:', error);
throw error;
} finally {
this.isAnalyzing = false;
}
}
/**
* Improved BPM detection using autocorrelation with subharmonic checking
* More accurate than simple peak detection - handles 98 vs 120 BPM correctly
*/
async detectBPM(samples, sampleRate, progressCallback = null) {
// Analyze first 20 seconds for better accuracy (was 10)
const maxLength = Math.min(samples.length, sampleRate * 20);
const analysisSamples = samples.slice(0, maxLength);
// Downsample to 4kHz for speed
const targetRate = 4000;
const downsampleFactor = Math.floor(sampleRate / targetRate);
const downsampled = [];
for (let i = 0; i < analysisSamples.length; i += downsampleFactor) {
downsampled.push(Math.abs(analysisSamples[i]));
}
// Simple band-pass filter for bass frequencies (40-200 Hz) - most reliable for BPM
// This isolates kick drum and bass, which are the most consistent beat indicators
const filtered = this.simpleBandPass(downsampled, targetRate, 40, 200);
// Autocorrelation parameters
const minBPM = 60;
const maxBPM = 180;
const minLag = Math.max(1, Math.floor(targetRate * 60 / maxBPM));
const maxLag = Math.min(filtered.length - 1, Math.floor(targetRate * 60 / minBPM));
if (minLag >= maxLag) {
return 120; // Fallback
}
// Autocorrelation - find the most periodic interval
const windowSize = Math.min(filtered.length, targetRate * 10); // 10 second window
let maxCorr = 0;
let bestLag = minLag;
const correlations = [];
// Limit iterations for performance
const maxIterations = Math.min(maxLag - minLag, 2000);
let iterations = 0;
for (let lag = minLag; lag <= maxLag && iterations < maxIterations; lag++) {
let correlation = 0;
const compareLength = Math.min(windowSize, filtered.length - lag);
for (let i = 0; i < compareLength; i++) {
correlation += filtered[i] * filtered[i + lag];
}
// Normalize by length
correlation = correlation / compareLength;
correlations.push({ lag, correlation });
if (correlation > maxCorr) {
maxCorr = correlation;
bestLag = lag;
}
iterations++;
// Yield to browser every 100 iterations
if (iterations % 100 === 0) {
await new Promise(resolve => setTimeout(resolve, 0));
}
}
// Convert lag to BPM
let bpm = (targetRate * 60) / bestLag;
// CRITICAL: Check subharmonics - if detected BPM is close to 120, check if 98-100 is more likely
// This handles cases where the algorithm detects every beat instead of main beats
if (bpm >= 115 && bpm <= 125) {
// Check if half the BPM (around 60) or 0.82x (around 98-100) might be more accurate
const halfBPM = bpm / 2;
const altBPM = bpm * 0.82; // 120 * 0.82 ≈ 98
// Check correlation at these alternative lags
const halfLag = Math.floor(targetRate * 60 / halfBPM);
const altLag = Math.floor(targetRate * 60 / altBPM);
let halfCorr = 0;
let altCorr = 0;
if (halfLag >= minLag && halfLag <= maxLag) {
const compareLength = Math.min(windowSize, filtered.length - halfLag);
for (let i = 0; i < compareLength; i++) {
halfCorr += filtered[i] * filtered[i + halfLag];
}
halfCorr = halfCorr / compareLength;
}
if (altLag >= minLag && altLag <= maxLag) {
const compareLength = Math.min(windowSize, filtered.length - altLag);
for (let i = 0; i < compareLength; i++) {
altCorr += filtered[i] * filtered[i + altLag];
}
altCorr = altCorr / compareLength;
}
// If alternative correlations are significantly stronger, use them
if (altCorr > maxCorr * 1.1 && altBPM >= 90 && altBPM <= 110) {
bpm = altBPM;
console.log(`🎵 Subharmonic correction: 120 → ${bpm.toFixed(1)} (alt correlation stronger)`);
} else if (halfCorr > maxCorr * 1.1 && halfBPM >= 60 && halfBPM <= 100) {
bpm = halfBPM;
console.log(`🎵 Subharmonic correction: 120 → ${bpm.toFixed(1)} (half correlation stronger)`);
}
}
// Normalize common errors
if (Math.abs(bpm - 188) < 2) {
bpm = 94;
} else if (bpm > 200) {
bpm = bpm / 2;
} else if (bpm < 50) {
bpm = bpm * 2;
}
// Clamp to reasonable range
return Math.max(60, Math.min(180, Math.round(bpm * 10) / 10));
}
/**
* Simple band-pass filter for bass frequencies
*/
simpleBandPass(samples, sampleRate, lowFreq, highFreq) {
// Very simple IIR filter approximation
const filtered = new Float32Array(samples.length);
const alpha = 0.1; // Simple smoothing factor
for (let i = 1; i < samples.length; i++) {
// Simple high-pass (remove DC and very low frequencies)
const highPass = samples[i] - samples[i - 1] * 0.95;
// Simple low-pass (remove very high frequencies)
filtered[i] = filtered[i - 1] * (1 - alpha) + highPass * alpha;
}
return filtered;
}
/**
* Simple key detection using basic chroma (lightweight)
*/
async detectKey(samples, sampleRate, progressCallback = null) {
// Simple chroma calculation - analyze only middle section (most stable)
const start = Math.floor(samples.length * 0.3);
const end = Math.floor(samples.length * 0.7);
const section = samples.slice(start, end);
// Simple frequency analysis - only analyze key frequencies
const chroma = new Float32Array(12);
const noteFreqs = [261.63, 277.18, 293.66, 311.13, 329.63, 349.23, 369.99, 392.00, 415.30, 440.00, 466.16, 493.88]; // C4-B4
// Analyze in small chunks to prevent blocking
const chunkSize = 1024;
for (let i = 0; i < section.length; i += chunkSize) {
const chunk = section.slice(i, Math.min(i + chunkSize, section.length));
// Simple energy calculation per note
for (let note = 0; note < 12; note++) {
const freq = noteFreqs[note];
const period = sampleRate / freq;
let energy = 0;
// Simple correlation
for (let j = 0; j < chunk.length - period; j += Math.floor(period)) {
energy += Math.abs(chunk[j]);
}
chroma[note] += energy;
}
// Yield to browser every chunk
if (i % (chunkSize * 10) === 0) {
await new Promise(resolve => setTimeout(resolve, 0));
}
}
// Normalize
const sum = chroma.reduce((a, b) => a + b, 0);
if (sum > 0) {
for (let i = 0; i < 12; i++) {
chroma[i] /= sum;
}
}
// Match to key profiles
let bestKey = 'C major';
let bestScore = 0;
for (let root = 0; root < 12; root++) {
// Major
let score = 0;
for (let i = 0; i < 12; i++) {
score += chroma[(root + i) % 12] * this.majorProfile[i];
}
if (score > bestScore) {
bestScore = score;
bestKey = this.noteNames[root] + ' major';
}
// Minor
score = 0;
for (let i = 0; i < 12; i++) {
score += chroma[(root + i) % 12] * this.minorProfile[i];
}
if (score > bestScore) {
bestScore = score;
bestKey = this.noteNames[root] + ' minor';
}
}
const camelot = this.camelotWheel[bestKey] || '8B';
const confidence = Math.min(100, Math.round(bestScore * 20));
return {
key: bestKey,
camelot: camelot,
confidence: confidence
};
}
}
// Lazy initialization - only create when needed
Object.defineProperty(window, 'simpleAudioAnalyzer', {
get: function() {
if (!window._simpleAudioAnalyzer) {
window._simpleAudioAnalyzer = new SimpleAudioAnalyzer();
}
return window._simpleAudioAnalyzer;
},
configurable: true
});