To blend data into a carrier signal. At the receiving side, a device demodulates the signals by separating the constant carrier signals from the variable data signals. For example, radio uses two types of modulation - amplitude modulation (AM) and frequency modulation (FM) - to mix audio signals with an AM or FM carrier signal. A modem modulates data by converting it to audible tones that can be transmitted on a telephone wire, and demodulates received signals to get the data.
