Tone.js/Tone/instrument/MetalSynth.ts

import { Envelope, EnvelopeOptions } from "../component/envelope/Envelope";
import { Filter } from "../component/filter/Filter";
import { Gain } from "../core/context/Gain";
import { ToneAudioNode, ToneAudioNodeOptions } from "../core/context/ToneAudioNode";
import { Cents, Frequency, NormalRange, Positive, Time } from "../core/type/Units";
import { deepMerge, omitFromObject, optionsFromArguments } from "../core/util/Defaults";
import { noOp, RecursivePartial } from "../core/util/Interface";
import { Multiply } from "../signal/Multiply";
import { Scale } from "../signal/Scale";
import { Signal } from "../signal/Signal";
import { FMOscillator } from "../source/oscillator/FMOscillator";
import { Monophonic, MonophonicOptions } from "./Monophonic";

export interface MetalSynthOptions extends MonophonicOptions {
	harmonicity: Positive;
	modulationIndex: Positive;
	octaves: number;
	resonance: Frequency;
	envelope: Omit<EnvelopeOptions, keyof ToneAudioNodeOptions>;
}

/**
 * Inharmonic ratio of frequencies based on the Roland TR-808
 * Taken from https://ccrma.stanford.edu/papers/tr-808-cymbal-physically-informed-circuit-bendable-digital-model
 */
const inharmRatios: number[] = [1.0, 1.483, 1.932, 2.546, 2.630, 3.897];

/**
 * A highly inharmonic and spectrally complex source with a highpass filter
 * and amplitude envelope which is good for making metallophone sounds.
 * Based on CymbalSynth by [@polyrhythmatic](https://github.com/polyrhythmatic).
 * Inspiration from [Sound on Sound](https://shorturl.at/rSZ12).
 */
export class MetalSynth extends Monophonic<MetalSynthOptions> {

	readonly name: string = "MetalSynth";

	/**
	 * The frequency of the cymbal
	 */
	readonly frequency: Signal<Frequency>;

	/**
	 * The detune applied to the oscillators
	 */
	readonly detune: Signal<Cents>;

	/**
	 * The array of FMOscillators
	 */
	private _oscillators: FMOscillator[] = [];

	/**
	 * The frequency multipliers
	 */
	private _freqMultipliers: Multiply[] = [];

	/**
	 * The gain node for the envelope.
	 */
	private _amplitude: Gain;

	/**
	 * Highpass the output
	 */
	private _highpass: Filter;

	/**
	 * The number of octaves the highpass
	 * filter frequency ramps
	 */
	private _octaves: number;

	/**
	 * Scale the body envelope for the highpass filter
	 */
	private _filterFreqScaler: Scale;

	/**
	 * The envelope which is connected both to the
	 * amplitude and a highpass filter's cutoff frequency.
	 * The lower-limit of the filter is controlled by the [[resonance]]
	 */
	readonly envelope: Envelope;

	constructor(options?: RecursivePartial<MetalSynthOptions>)
	constructor() {
		super(optionsFromArguments(MetalSynth.getDefaults(), arguments));
		const options = optionsFromArguments(MetalSynth.getDefaults(), arguments);

		this.detune = new Signal({
			context: this.context,
			units: "cents",
			value: options.detune,
		});

		this.frequency = new Signal({
			context: this.context,
			units: "frequency",
		});

		this._amplitude = new Gain({
			context: this.context,
			gain: 0,
		}).connect(this.output);

		this._highpass = new Filter({
			Q: -3.0102999566398125,
			context: this.context,
			type: "highpass",
		}).connect(this._amplitude);

		for (let i = 0; i < inharmRatios.length; i++) {
			const osc = new FMOscillator({
				context: this.context,
				harmonicity: options.harmonicity,
				modulationIndex: options.modulationIndex,
				modulationType: "square",
				onstop: i === 0 ? () => this.onsilence(this) : noOp,
				type: "square",
			});
			osc.connect(this._highpass);
			this._oscillators[i] = osc;

			const mult = new Multiply({
				context: this.context,
				value: inharmRatios[i],
			});
			this._freqMultipliers[i] = mult;
			this.frequency.chain(mult, osc.frequency);
			this.detune.connect(osc.detune);
		}

		this._filterFreqScaler = new Scale({
			context: this.context,
			max: 7000,
			min: this.toFrequency(options.resonance),
		});

		this.envelope = new Envelope({
			attack: options.envelope.attack,
			attackCurve: "linear",
			context: this.context,
			decay: options.envelope.decay,
			release: options.envelope.release,
			sustain: 0,
		});

		this.envelope.chain(this._filterFreqScaler, this._highpass.frequency);
		this.envelope.connect(this._amplitude.gain);
		// set the octaves
		this._octaves = options.octaves;
		this.octaves = options.octaves;
	}

	static getDefaults(): MetalSynthOptions {
		return deepMerge(Monophonic.getDefaults(), {
			envelope: Object.assign(
				omitFromObject(Envelope.getDefaults(), Object.keys(ToneAudioNode.getDefaults())),
				{
					attack: 0.001,
					decay: 1.4,
					release: 0.2,
				},
			),
			harmonicity: 5.1,
			modulationIndex: 32,
			octaves: 1.5,
			resonance: 4000,
		});
	}

	/**
	 * Trigger the attack.
	 * @param time When the attack should be triggered.
	 * @param velocity The velocity that the envelope should be triggered at.
	 */
	protected _triggerEnvelopeAttack(time: Time, velocity: NormalRange = 1): this {
		this.envelope.triggerAttack(time, velocity);
		this._oscillators.forEach(osc => osc.start(time));
		if (this.envelope.sustain === 0) {
			this._oscillators.forEach(osc => {
				osc.stop(this.toSeconds(time) + this.toSeconds(this.envelope.attack) + this.toSeconds(this.envelope.decay));
			});
		}
		return this;
	}

	/**
	 * Trigger the release of the envelope.
	 * @param time When the release should be triggered.
	 */
	protected _triggerEnvelopeRelease(time: Time): this {
		this.envelope.triggerRelease(time);
		this._oscillators.forEach(osc => osc.stop(this.toSeconds(time) + this.toSeconds(this.envelope.release)));
		return this;
	}

	/**
	 * The modulationIndex of the oscillators which make up the source.
	 * see [[FMOscillator.modulationIndex]]
	 */
	get modulationIndex(): number {
		return this._oscillators[0].modulationIndex.value;
	}
	set modulationIndex(val) {
		this._oscillators.forEach(osc => (osc.modulationIndex.value = val));
	}

	/**
	 * The harmonicity of the oscillators which make up the source.
	 * see Tone.FMOscillator.harmonicity
	 */
	get harmonicity(): number {
		return this._oscillators[0].harmonicity.value;
	}
	set harmonicity(val) {
		this._oscillators.forEach(osc => (osc.harmonicity.value = val));
	}

	/**
	 * The lower level of the highpass filter which is attached to the envelope.
	 * This value should be between [0, 7000]
	 * @min 0
	 * @max 7000
	 */
	get resonance(): Frequency {
		return this._filterFreqScaler.min;
	}
	set resonance(val) {
		this._filterFreqScaler.min = this.toFrequency(val);
		this.octaves = this._octaves;
	}

	/**
	 * The number of octaves above the "resonance" frequency
	 * that the filter ramps during the attack/decay envelope
	 */
	get octaves(): number {
		return this._octaves;
	}
	set octaves(val) {
		this._octaves = val;
		this._filterFreqScaler.max = this._filterFreqScaler.min * Math.pow(2, val);
	}

	dispose(): this {
		super.dispose();
		this._oscillators.forEach(osc => osc.dispose());
		this._freqMultipliers.forEach(freqMult => freqMult.dispose());
		this.frequency.dispose();
		this.detune.dispose();
		this._filterFreqScaler.dispose();
		this._amplitude.dispose();
		this.envelope.dispose();
		this._highpass.dispose();
		return this;
	}
}