music-of-life/additive-processor.js

class AdditiveProcessor 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 arrays
        this.freq = new Float32Array(this.MAX_PARTIALS);
        this.amp = new Float32Array(this.MAX_PARTIALS);
        this.phase = new Float32Array(this.MAX_PARTIALS);

        this.targetFreq = new Float32Array(this.MAX_PARTIALS);
        this.targetAmp = new Float32Array(this.MAX_PARTIALS);

        this.activeCount = 0;
        this.targetCount = 0;

        // LPF state
        this.lastSample = 0;

        this.port.onmessage = e => {
            const { freqs, amps } = e.data;
            let count = freqs.length;

            if (count > this.MAX_PARTIALS) {
                // Supercell aggregation
                const factor = count / this.MAX_PARTIALS;
                for (let i = 0; i < this.MAX_PARTIALS; i++) {
                    let sumFreq = 0, sumAmp = 0;
                    const start = Math.floor(i * factor);
                    const end = Math.floor((i + 1) * factor);
                    for (let j = start; j < end; j++) {
                        sumFreq += freqs[j];
                        sumAmp += amps[j];
                    }
                    this.targetFreq[i] = sumFreq / (end - start);
                    this.targetAmp[i] = sumAmp / (end - start);

                    if (this.freq[i] === 0) this.phase[i] = Math.random();
                }
                this.targetCount = this.MAX_PARTIALS;
            } else {
                // Direct assignment
                this.targetFreq.set(freqs);
                this.targetAmp.set(amps);
                for (let i = 0; i < count; i++) {
                    if (this.freq[i] === 0) this.phase[i] = Math.random();
                }
                this.targetCount = count;
            }
        };
    }

    process(_, outputs) {
        const out = outputs[0][0];

        const COUNT_SMOOTH = 0.02;
        this.activeCount += (this.targetCount - this.activeCount) * COUNT_SMOOTH;
        const count = Math.floor(this.activeCount);

        if (count === 0) {
            out.fill(0);
            return true;
        }

        // Dynamic smoothing
        const AMP_SMOOTH = 0.01 * Math.min(count / 50, 1);
        const FREQ_SMOOTH = 0.01 * Math.min(count / 50, 1);

        const srInv = 1 / sampleRate;
        const tableSize = this.SINE_TABLE_SIZE;

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

            for (let c = 0; c < count; c++) {
                this.freq[c] += (this.targetFreq[c] - this.freq[c]) * FREQ_SMOOTH;
                this.amp[c] += (this.targetAmp[c] - this.amp[c]) * AMP_SMOOTH;

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

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

            // Only apply soft LPF if we have more than a few partials
            const useLPF = count >= 4;
            if (useLPF) {
                out[i] = this.lastSample * 0.95 + sample * 0.05;
                this.lastSample = out[i];
            } else {
                out[i] = sample;
            }
        }

        return true;
    }
}

registerProcessor('additive-processor', AdditiveProcessor);