Tone.js/Tone/effect/AutoWah.ts

import { Effect, EffectOptions } from "./Effect";
import { Filter } from "../component/filter/Filter";
import { Follower } from "../component/analysis/Follower";
import { Decibels, Frequency, GainFactor, Hertz, Positive, Time } from "../core/type/Units";
import { optionsFromArguments } from "../core/util/Defaults";
import { Gain } from "../core/context/Gain";
import { dbToGain, gainToDb } from "../core/type/Conversions";
import { ScaleExp } from "../signal/ScaleExp";
import { Signal } from "../signal/Signal";
import { readOnly } from "../core/util/Interface";

export interface AutoWahOptions extends EffectOptions {
	baseFrequency: Frequency;
	octaves: Positive;
	sensitivity: Decibels;
	Q: Positive;
	gain: GainFactor;
	follower: Time;
}

/**
 * AutoWah connects a [[Follower]] to a [[Filter]]. 
 * The frequency of the filter, follows the input amplitude curve. 
 * Inspiration from [Tuna.js](https://github.com/Dinahmoe/tuna).
 * 
 * @example
 * const autoWah = new Tone.AutoWah(50, 6, -30).toDestination();
 * // initialize the synth and connect to autowah
 * const synth = new Tone.Synth().connect(autoWah);
 * // Q value influences the effect of the wah - default is 2
 * autoWah.Q.value = 6;
 * // more audible on higher notes
 * synth.triggerAttackRelease("C4", "8n");
 * @category Effect
 */
export class AutoWah extends Effect<AutoWahOptions> {

	readonly name: string = "AutoWah";

	/**
	 * The envelope follower. Set the attack/release
	 * timing to adjust how the envelope is followed.
	 */
	private _follower: Follower;

	/**
	 * scales the follower value to the frequency domain
	 */
	private _sweepRange: ScaleExp;

	/**
	 * Hold the base frequency value
	 */
	private _baseFrequency: Hertz;

	/**
	 * Private holder for the octave count
	 */
	private _octaves: Positive;

	/**
	 * the input gain to adjust the sensitivity
	 */
	private _inputBoost: Gain;

	/**
	 * Private holder for the filter
	 */
	private _bandpass: Filter;

	/**
	 * The peaking fitler
	 */
	private _peaking: Filter;

	/**
	 * The gain of the filter.
	 */
	readonly gain: Signal<"decibels">;

	/**
	 * The quality of the filter.
	 */
	readonly Q: Signal<"positive">;

	/**
	 * @param baseFrequency The frequency the filter is set to at the low point of the wah
	 * @param octaves The number of octaves above the baseFrequency the filter will sweep to when fully open. 
	 * @param sensitivity The decibel threshold sensitivity for the incoming signal. Normal range of -40 to 0.
	 */
	constructor(baseFrequency?: Frequency, octaves?: Positive, sensitivity?: Decibels);
	constructor(options?: Partial<AutoWahOptions>);
	constructor() {

		super(optionsFromArguments(AutoWah.getDefaults(), arguments, ["baseFrequency", "octaves", "sensitivity"]));
		const options = optionsFromArguments(AutoWah.getDefaults(), arguments, ["baseFrequency", "octaves", "sensitivity"]);

		this._follower = new Follower({
			context: this.context,
			smoothing: options.follower,
		});
		this._sweepRange = new ScaleExp({
			context: this.context,
			min: 0,
			max: 1,
			exponent: 0.5,
		});
		this._baseFrequency = this.toFrequency(options.baseFrequency);
		this._octaves = options.octaves;
		this._inputBoost = new Gain({ context: this.context });
		this._bandpass = new Filter({
			context: this.context,
			rolloff: -48,
			frequency: 0,
			Q: options.Q,
		});
		this._peaking = new Filter({
			context: this.context,
			type: "peaking"
		});
		this._peaking.gain.value = options.gain;
		this.gain = this._peaking.gain;
		this.Q = this._bandpass.Q;

		// the control signal path
		this.effectSend.chain(this._inputBoost, this._follower, this._sweepRange);
		this._sweepRange.connect(this._bandpass.frequency);
		this._sweepRange.connect(this._peaking.frequency);
		// the filtered path
		this.effectSend.chain(this._bandpass, this._peaking, this.effectReturn);
		// set the initial value
		this._setSweepRange();
		this.sensitivity = options.sensitivity;

		readOnly(this, ["gain", "Q"]);
	}

	static getDefaults(): AutoWahOptions {
		return Object.assign(Effect.getDefaults(), {
			baseFrequency: 100,
			octaves: 6,
			sensitivity: 0,
			Q: 2,
			gain: 2,
			follower: 0.2,
		});
	}

	/**
	 * The number of octaves that the filter will sweep above the baseFrequency.
	 */
	get octaves() {
		return this._octaves;
	}
	set octaves(octaves) {
		this._octaves = octaves;
		this._setSweepRange();
	}

	/**
	 * The follower's smoothing time
	 */
	get follower(): Time {
		return this._follower.smoothing;
	}
	set follower(follower) {
		this._follower.smoothing = follower;
	}

	/**
	 * The base frequency from which the sweep will start from.
	 */
	get baseFrequency(): Frequency {
		return this._baseFrequency;
	}
	set baseFrequency(baseFreq) {
		this._baseFrequency = this.toFrequency(baseFreq);
		this._setSweepRange();
	}

	/**
	 * The sensitivity to control how responsive to the input signal the filter is.
	 */
	get sensitivity(): Decibels {
		return gainToDb(1 / this._inputBoost.gain.value);
	}
	set sensitivity(sensitivity) {
		this._inputBoost.gain.value = 1 / dbToGain(sensitivity);
	}

	/**
	 * sets the sweep range of the scaler
	 */
	private _setSweepRange() {
		this._sweepRange.min = this._baseFrequency;
		this._sweepRange.max = Math.min(this._baseFrequency * Math.pow(2, this._octaves), this.context.sampleRate / 2);
	}

	dispose(): this {
		super.dispose();
		this._follower.dispose();
		this._sweepRange.dispose();
		this._bandpass.dispose();
		this._peaking.dispose();
		this._inputBoost.dispose();
		return this;
	}
}