FeedbackCombFilter.ts

import { Delay } from "../../core/context/Delay";
import { Gain } from "../../core/context/Gain";
import { Param } from "../../core/context/Param";
import { InputNode, OutputNode, ToneAudioNode, ToneAudioNodeOptions } from "../../core/context/ToneAudioNode";
import { NormalRange, Time } from "../../core/type/Units";
import { optionsFromArguments } from "../../core/util/Defaults";
import { RecursivePartial } from "../../core/util/Interface";

export interface FeedbackCombFilterOptions extends ToneAudioNodeOptions {
	delayTime: Time;
	resonance: NormalRange;
}

/**
 * Comb filters are basic building blocks for physical modeling. Read more
 * about comb filters on [CCRMA's website](https://ccrma.stanford.edu/~jos/pasp/Feedback_Comb_Filters.html).
 */
export class FeedbackCombFilter extends ToneAudioNode<FeedbackCombFilterOptions> {
	
	readonly name = "FeedbackCombFilter";
	
	/**
	 * The delay node
	 */
	private _delay: Delay;
	
	/**
	 * The feedback node
	 */
	private _feedback: Gain;
	
	/**
	 * The amount of delay of the comb filter.
	 */
	readonly delayTime: Param<Time>;
	
	/**
	 * The amount of feedback of the delayed signal.
	 */
	readonly resonance: Param<NormalRange>;
	
	readonly input: InputNode;
	readonly output: OutputNode;
	
	/**
	 * @param delayTime The delay time of the filter.
	 * @param resonance The amount of feedback the filter has.
	 */
	constructor(delayTime?: Time, resonance?: NormalRange);
	constructor(options?: RecursivePartial<FeedbackCombFilterOptions>);
	constructor() {
		super(optionsFromArguments(FeedbackCombFilter.getDefaults(), arguments, ["delayTime", "resonance"]));
		const options = optionsFromArguments(FeedbackCombFilter.getDefaults(), arguments, ["delayTime", "resonance"]);

		this._delay = this.input = this.output = new Delay({
			context: this.context,
			delayTime: options.delayTime
		});
		this.delayTime = this._delay.delayTime;

		this._feedback = new Gain({
			context: this.context,
			gain: options.resonance
		});
		this.resonance = this._feedback.gain;

		this._delay.chain(this._feedback, this._delay);
	}

	/**
	 * The default parameters
	 */
	static getDefaults(): FeedbackCombFilterOptions {
		return Object.assign(ToneAudioNode.getDefaults(), {
			delayTime: 0.1,
			resonance: 0.5,
		});
	}

	dispose(): this {
		super.dispose();
		this._delay.dispose();
		this._feedback.dispose();
		return this;
	}
}