Tone.js/Tone/effect/JCReverb.ts

import { NormalRange } from "../core/type/Units";
import { StereoEffect, StereoEffectOptions } from "./StereoEffect";
import { optionsFromArguments } from "../core/util/Defaults";
import { Scale } from "../signal/Scale";
import { Signal } from "../signal/Signal";
import { FeedbackCombFilter } from "../component/filter/FeedbackCombFilter";
import { readOnly } from "../core/util/Interface";

export interface JCReverbOptions extends StereoEffectOptions {
	roomSize: NormalRange;
}

/**
 * an array of the comb filter delay time values
 */
const combFilterDelayTimes = [1687 / 25000, 1601 / 25000, 2053 / 25000, 2251 / 25000];

/**
 * the resonances of each of the comb filters
 */
const combFilterResonances = [0.773, 0.802, 0.753, 0.733];

/**
 * the allpass filter frequencies
 */
const allpassFilterFreqs = [347, 113, 37];

/**
 * JCReverb is a simple [Schroeder Reverberator](https://ccrma.stanford.edu/~jos/pasp/Schroeder_Reverberators.html)
 * tuned by John Chowning in 1970.
 * It is made up of three allpass filters and four [[FeedbackCombFilter]].
 * JCReverb is now implemented with an AudioWorkletNode which may result on performance degradation on some platforms. Consider using [[Reverb]].
 * @example
 * const reverb = new Tone.JCReverb(0.4).toDestination();
 * const delay = new Tone.FeedbackDelay(0.5);
 * // connecting the synth to reverb through delay
 * const synth = new Tone.DuoSynth().chain(delay, reverb);
 * synth.triggerAttackRelease("A4", "8n");
 * 
 * @category Effect
 */
export class JCReverb extends StereoEffect<JCReverbOptions> {

	readonly name: string = "JCReverb";

	/**
	 * Room size control values. 
	 */
	readonly roomSize: Signal<"normalRange">

	/**
	 * Scale the room size
	 */
	private _scaleRoomSize: Scale;

	/**
	 * a series of allpass filters
	 */
	private _allpassFilters: BiquadFilterNode[] = [];

	/**
	 * parallel feedback comb filters
	 */
	private _feedbackCombFilters: FeedbackCombFilter[] = [];

	/**
	 * @param roomSize Correlated to the decay time.
	 */
	constructor(roomSize?: NormalRange);
	constructor(options?: Partial<JCReverbOptions>);
	constructor() {

		super(optionsFromArguments(JCReverb.getDefaults(), arguments, ["roomSize"]));
		const options = optionsFromArguments(JCReverb.getDefaults(), arguments, ["roomSize"]);

		this.roomSize = new Signal({
			context: this.context,
			value: options.roomSize,
			units: "normalRange",
		});
		this._scaleRoomSize = new Scale({
			context: this.context,
			min: -0.733,
			max: 0.197,
		});

		// make the allpass filters
		this._allpassFilters = allpassFilterFreqs.map(freq => {
			const allpass = this.context.createBiquadFilter();
			allpass.type = "allpass";
			allpass.frequency.value = freq;
			return allpass;
		});

		// and the comb filters
		this._feedbackCombFilters = combFilterDelayTimes.map((delayTime, index) => {
			const fbcf = new FeedbackCombFilter({
				context: this.context,
				delayTime,
			});
			this._scaleRoomSize.connect(fbcf.resonance);
			fbcf.resonance.value = combFilterResonances[index];
			if (index < combFilterDelayTimes.length / 2) {
				this.connectEffectLeft(...this._allpassFilters, fbcf);
			} else {
				this.connectEffectRight(...this._allpassFilters, fbcf);
			}
			return fbcf;
		});

		// chain the allpass filters together
		this.roomSize.connect(this._scaleRoomSize);
		readOnly(this, ["roomSize"]);
	}

	static getDefaults(): JCReverbOptions {
		return Object.assign(StereoEffect.getDefaults(), {
			roomSize: 0.5,
		});
	}

	dispose(): this {
		super.dispose();
		this._allpassFilters.forEach(apf => apf.disconnect());
		this._feedbackCombFilters.forEach(fbcf => fbcf.dispose());
		this.roomSize.dispose();
		this._scaleRoomSize.dispose();
		return this;
	}
}