Tone.js/Tone/effect/FrequencyShifter.ts

import { PhaseShiftAllpass } from "../component/filter/PhaseShiftAllpass";
import { Frequency } from "../core/type/Units";
import { optionsFromArguments } from "../core/util/Defaults";
import { Effect, EffectOptions } from "../effect/Effect";
import { Add } from "../signal/Add";
import { Multiply } from "../signal/Multiply";
import { Negate } from "../signal/Negate";
import { Signal } from "../signal/Signal";
import { Oscillator } from "../source/oscillator/Oscillator";
import { ToneOscillatorNode } from "../source/oscillator/ToneOscillatorNode";

interface FrequencyShifterOptions extends EffectOptions {
	frequency: Frequency;
}

/**
 * FrequencyShifter can be used to shift all frequencies of a signal by a fixed amount.
 * The amount can be changed at audio rate and the effect is applied in real time.
 * The frequency shifting is implemented with a technique called single side band modulation using a ring modulator.
 * Note: Contrary to pitch shifting, all frequencies are shifted by the same amount,
 * destroying the harmonic relationship between them. This leads to the classic ring modulator timbre distortion.
 * The algorithm will produces some aliasing towards the high end, especially if your source material
 * contains a lot of high frequencies. Unfortunatelly the webaudio API does not support resampling
 * buffers in real time, so it is not possible to fix it properly. Depending on the use case it might
 * be an option to low pass filter your input before frequency shifting it to get ride of the aliasing.
 * You can find a very detailed description of the algorithm here: https://larzeitlin.github.io/RMFS/
 *
 * @example
 * import { FrequencyShifter, Oscillator } from "tone";
 * const input = new Oscillator(230, "sawtooth").start();
 * const shift = new FrequencyShifter(42).toDestination();
 * input.connect(shift);
 * @category Effect
 */
export class FrequencyShifter extends Effect<FrequencyShifterOptions> {

	readonly name: string = "FrequencyShifter";

	/**
	 * The ring modulators carrier frequency. This frequency determines
	 * by how many Hertz the input signal will be shifted up or down. Default is 0.
	 */
	readonly frequency: Signal<"frequency">;

	/**
	 * The ring modulators sine carrier
	 */
	private _sine: ToneOscillatorNode;

	/**
	 * The ring modulators cosine carrier
	 */
	private _cosine: Oscillator;

	/**
	 * The sine multiply operator
	 */
	private _sineMultiply: Multiply;

	/**
	 * The cosine multiply operator
	 */
	private _cosineMultiply: Multiply;

	/**
	 * The negate operator
	 */
	private _negate: Negate;

	/**
	 * The final add operator
	 */
	private _add: Add;

	/**
	 * The phase shifter to create the initial 90° phase offset
	 */
	private _phaseShifter: PhaseShiftAllpass;

	/**
	 * @param frequency The incoming signal is shifted by this frequency value.
	 */
	constructor(frequency?: Frequency);
	constructor(options?: Partial<FrequencyShifterOptions>);
	constructor() {

		super(optionsFromArguments(FrequencyShifter.getDefaults(), arguments, ["frequency"]));
		const options = optionsFromArguments(FrequencyShifter.getDefaults(), arguments, ["frequency"]);

		this.frequency = new Signal({
			context: this.context,
			units: "frequency",
			value: options.frequency,
			minValue: -this.context.sampleRate/2,
			maxValue: this.context.sampleRate/2,
		});

		this._sine = new ToneOscillatorNode({
			context: this.context,
			type: "sine",
		});

		this._cosine = new Oscillator({
			context: this.context,
			phase: -90,
			type: "sine",
		});

		this._sineMultiply = new Multiply({ context: this.context });
		this._cosineMultiply = new Multiply({ context: this.context });
		this._negate = new Negate({ context: this.context });
		this._add = new Add({ context: this.context });

		this._phaseShifter = new PhaseShiftAllpass({ context: this.context });
		this.effectSend.connect(this._phaseShifter);

		// connect the carrier frequency signal to the two oscillators
		this.frequency.fan(this._sine.frequency, this._cosine.frequency);

		this._phaseShifter.offset90.connect(this._cosineMultiply);
		this._cosine.connect(this._cosineMultiply.factor);

		this._phaseShifter.connect(this._sineMultiply);
		this._sine.connect(this._sineMultiply.factor);
		this._sineMultiply.connect(this._negate);

		this._cosineMultiply.connect(this._add);
		this._negate.connect(this._add.addend);

		this._add.connect(this.effectReturn);

		// start the oscillators at the same time
		const now = this.immediate();
		this._sine.start(now);
		this._cosine.start(now);
	}

	static getDefaults(): FrequencyShifterOptions {
		return Object.assign(Effect.getDefaults(), {
			frequency: 0,
		});
	}

	dispose(): this {
		super.dispose();
		this.frequency.dispose();
		this._add.dispose();
		this._cosine.dispose();
		this._cosineMultiply.dispose();
		this._negate.dispose();
		this._phaseShifter.dispose();
		this._sine.dispose();
		this._sineMultiply.dispose();
		return this;
	}
}