Tone.js/Tone/effect/Distortion.ts

import { optionsFromArguments } from "../core/util/Defaults";
import { WaveShaper } from "../signal/WaveShaper";
import { Effect, EffectOptions } from "./Effect";

export interface DistortionOptions extends EffectOptions {
	distortion: number;
	oversample: OverSampleType;
}

/**
 * A simple distortion effect using Tone.WaveShaper.
 * Algorithm from [this stackoverflow answer](http://stackoverflow.com/a/22313408).
 *
 * @example
 * const dist = new Tone.Distortion(0.8).toDestination();
 * const fm = new Tone.FMSynth().connect(dist);
 * fm.triggerAttackRelease("A1", "8n");
 * @category Effect
 */
export class Distortion extends Effect<DistortionOptions> {

	readonly name: string = "Distortion";

	/**
	 * The waveshaper which does the distortion
	 */
	private _shaper: WaveShaper;

	/**
	 * Stores the distortion value
	 */
	private _distortion: number;

	/**
	 * @param distortion The amount of distortion (nominal range of 0-1)
	 */
	constructor(distortion?: number);
	constructor(options?: Partial<DistortionOptions>);
	constructor() {

		super(optionsFromArguments(Distortion.getDefaults(), arguments, ["distortion"]));
		const options = optionsFromArguments(Distortion.getDefaults(), arguments, ["distortion"]);

		this._shaper = new WaveShaper({
			context: this.context,
			length: 4096,
		});

		this._distortion = options.distortion;

		this.connectEffect(this._shaper);
		this.distortion = options.distortion;
		this.oversample = options.oversample;
	}

	static getDefaults(): DistortionOptions {
		return Object.assign(Effect.getDefaults(), {
			distortion: 0.4,
			oversample: "none" as OverSampleType,
		});
	}

	/**
	 * The amount of distortion. Nominal range is between 0 and 1.
	 */
	get distortion(): number {
		return this._distortion;
	}
	set distortion(amount) {
		this._distortion = amount;
		const k = amount * 100;
		const deg = Math.PI / 180;
		this._shaper.setMap((x) => {
			if (Math.abs(x) < 0.001) {
				// should output 0 when input is 0
				return 0;
			} else {
				return (3 + k) * x * 20 * deg / (Math.PI + k * Math.abs(x));
			}
		});
	}

	/**
	 * The oversampling of the effect. Can either be "none", "2x" or "4x".
	 */
	get oversample(): OverSampleType {
		return this._shaper.oversample;
	}
	set oversample(oversampling) {
		this._shaper.oversample = oversampling;
	}

	dispose(): this {
		super.dispose();
		this._shaper.dispose();
		return this;
	}
}