murmuraba/dist/utils/simple-agc.js

Real-time audio noise reduction with advanced chunked processing for web applications

/**
 * Simple Automatic Gain Control - REFACTORED
 * Based on WebSearch results for Web Audio API AGC
 *
 * Key findings from WebSearch:
 * - Use DynamicsCompressorNode for reducing dynamics range
 * - Use AnalyserNode + GainNode for manual AGC
 * - Always use setTargetAtTime to prevent clicks
 * - RMS calculation for accurate level detection
 */
export class SimpleAGC {
    constructor(audioContext, targetLevel = 0.5) {
        this.audioContext = audioContext;
        this.targetLevel = targetLevel;
        this.attackTime = 0.08; // 80ms attack - balanced response for voice
        this.releaseTime = 0.4; // 400ms release - smooth adaptation
        this.maxGain = 3.5; // 3.5x maximum gain for safe louder output
        // Create nodes as per WebSearch recommendation
        this.analyser = audioContext.createAnalyser();
        this.gainNode = audioContext.createGain();
        // Configure analyser for time-domain analysis
        this.analyser.fftSize = 256;
        this.bufferLength = this.analyser.frequencyBinCount;
        this.dataArray = new Uint8Array(this.bufferLength);
        // Connect nodes
        this.analyser.connect(this.gainNode);
    }
    /**
     * Update gain based on current audio level
     * Implements attack/release timing as recommended by WebSearch
     */
    updateGain() {
        const currentRMS = this.calculateRMS();
        // Only adjust if we have signal (avoid divide by zero)
        if (currentRMS > 0) {
            const targetGain = this.calculateTargetGain(currentRMS);
            this.applyGainSmoothing(targetGain);
        }
    }
    /**
     * Calculate RMS (Root Mean Square) level
     * Formula from WebSearch MDN examples
     */
    calculateRMS() {
        this.analyser.getByteTimeDomainData(this.dataArray);
        let sum = 0;
        for (let i = 0; i < this.bufferLength; i++) {
            // Convert from 0-255 to -1 to 1
            const normalized = (this.dataArray[i] - 128) / 128;
            sum += normalized * normalized;
        }
        return Math.sqrt(sum / this.bufferLength);
    }
    /**
     * Calculate target gain with safety limits
     */
    calculateTargetGain(currentRMS) {
        const rawGain = this.targetLevel / currentRMS;
        return Math.min(rawGain, this.maxGain);
    }
    /**
     * Apply gain with proper timing to prevent clicks
     * Uses exponential ramp as per WebSearch recommendation
     */
    applyGainSmoothing(targetGain) {
        const currentGain = this.gainNode.gain.value;
        const isIncreasing = targetGain > currentGain;
        // Use attack time when increasing, release time when decreasing
        const timeConstant = isIncreasing ? this.attackTime : this.releaseTime;
        this.gainNode.gain.setTargetAtTime(targetGain, this.audioContext.currentTime, timeConstant);
    }
    /**
     * Get current gain value for monitoring
     */
    getCurrentGain() {
        return this.gainNode.gain.value;
    }
    /**
     * Connect source -> analyser -> gain -> destination
     */
    connect(source, destination) {
        source.connect(this.analyser);
        this.gainNode.connect(destination);
    }
}