Glossary definition of Modulation

Modulation is the process by which a carrier frequency or wave has an information signal (e.g. voice, data, or image) added to it, so that the information can be transmitted over a communications system. For example, a modem modulates digital data into audible tones for transmission over the telephone network.

Two well-known types of analogue modulation are produced by varying the carrier's amplitude (AM or amplitude modulation), or its frequency (FM, or frequency modulation). Digital modulation often uses various types of pulse code modulation (PCM).