tone/Tone/effect/JCReverb.ts

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

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 {@link FeedbackCombFilter}.
 * JCReverb is now implemented with an AudioWorkletNode which may result on performance degradation on some platforms. Consider using {@link 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() {
		const options = optionsFromArguments(
			JCReverb.getDefaults(),
			arguments,
			["roomSize"]
		);
		super(options);

		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;
	}
}