function stop(sound_name, id) {
	if (typeof sound_name !== "undefined") {
		const sound = audioTracks[sound_name];
		if (sound && typeof sound !== "undefined") {
			sound.stop(id);
			// remove the defined onend callback (if any defined)
			sound.off("end", undefined, id);
		} else {
			throw new Error("audio clip " + sound_name + " does not exist");
		}
	} else {
		Howler.stop();
	}
}
stop the specified sound on all channels
@param {string} [sound_name] - audio clip name (case sensitive). If none is passed, all sounds are stopped.
@param {number} [id] - the sound instance ID. If none is passed, all sounds in group will stop.
@example
me.audio.stop("cling");