music-of-life/granular-processor.js

class GranularProcessor extends AudioWorkletProcessor {
    constructor() {
        super();

        this.MAX_PARTIALS = 500;

        // Sine lookup table
        this.SINE_TABLE_SIZE = 4096;
        this.sineTable = new Float32Array(this.SINE_TABLE_SIZE);
        for (let i = 0; i < this.SINE_TABLE_SIZE; i++) {
            this.sineTable[i] = Math.sin((i / this.SINE_TABLE_SIZE) * 2 * Math.PI);
        }

        // Partial state
        this.freq = new Float32Array(this.MAX_PARTIALS);
        this.phase = new Float32Array(this.MAX_PARTIALS);
        this.amp = new Float32Array(this.MAX_PARTIALS);
        this.envPhase = new Float32Array(this.MAX_PARTIALS);
        this.envDuration = new Float32Array(this.MAX_PARTIALS);

        this.targetCount = 0;

        this.port.onmessage = e => {
            const { freqs, amps, durations } = e.data;
            const count = freqs.length;
            let factor = 1;
            if (count > this.MAX_PARTIALS) factor = count / this.MAX_PARTIALS;

            for (let i = 0; i < this.MAX_PARTIALS && i * factor < count; i++) {
                const start = Math.floor(i * factor);
                const end = Math.floor((i + 1) * factor);

                let sumFreq = 0;
                let sumAmp = 0;
                let sumDur = 0;

                for (let j = start; j < end; j++) {
                    sumFreq += freqs[j];
                    sumAmp += amps[j];
                    sumDur += durations[j];
                }

                const n = end - start;
                this.freq[i] = sumFreq / n;
                this.amp[i] = (sumAmp / n) * 1.5; // louder
                this.envDuration[i] = sumDur / n;
                this.envPhase[i] = 0;
            }

            this.targetCount = Math.min(count, this.MAX_PARTIALS);
        };
    }

    process(_, outputs) {
        const out = outputs[0][0];
        const srInv = 1 / sampleRate;

        const attackTime = 0.005;        // 5ms attack
        const decayTimeFactor = 1.2;     // longer decay
        const expFactor = 5;             // controls exponential decay speed

        for (let i = 0; i < out.length; i++) {
            let sample = 0;

            for (let c = 0; c < this.targetCount; c++) {
                let env = 0;

                if (this.envPhase[c] < 1) {
                    const t = this.envPhase[c] * this.envDuration[c];

                    if (t < attackTime) {
                        // linear attack
                        env = t / attackTime;
                    } else {
                        // exponential decay
                        const decayTime = this.envDuration[c] * decayTimeFactor;
                        const decayProgress = (t - attackTime) / Math.max(decayTime, 0.001);
                        env = Math.exp(-expFactor * decayProgress);
                    }

                    this.envPhase[c] += srInv / Math.max(this.envDuration[c], 0.001);
                }

                this.phase[c] += this.freq[c] * srInv;
                if (this.phase[c] >= 1) this.phase[c] -= 1;

                const idx = Math.floor(this.phase[c] * this.SINE_TABLE_SIZE) % this.SINE_TABLE_SIZE;
                sample += this.sineTable[idx] * this.amp[c] * env;
            }

            // soft limiting
            if (sample > 1) sample = 1;
            else if (sample < -1) sample = -1;

            out[i] = sample;
        }

        return true;
    }
}

registerProcessor('granular-processor', GranularProcessor);