modulation

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(n.) A change in the characteristics of a signal. When a carrier signal is modulated by or mixed with another signal, it is encoded with information that is analogous to information contained in another signal. The carrier transmits both signals. If the original carrier signal is of a constant level, changes in the composite signal represent the signal it is carrying. The opposite process is demodulation, or decoding of the data. A modem modulates a signal to transmit, and demodulates it to receive.