The audio fidelity of this technique is further decreased by the lack of a properly sized dynamic loudspeaker, even moreso in modern machines and particularly laptops, that use a tiny moving-iron speaker (often confused with piezoelectric). The reason for this is that PWM-produced audio requires a low-pass filter before the final output in order to suppress switching noise and high harmonics, something that a normal dynamic loudspeaker can do on its own right, while the tiny metal diaphragm of the moving-iron speaker will let much switching noise pass, as will many direct couplings (though there are exceptions to this, e.g. filtered "speaker in" ports on some motherboards and sound cards).