Modulation
In electronics and telecommunications,
modulation is the process of varying one or more properties of a periodic waveform, called the
carrier signal, with a modulating signal that typically contains information to be transmitted. In telecommunications, modulation is the process of conveying a message signal, for example a digital bit stream or an analog audio signal, inside another signal that can be physically transmitted. Modulation of a sine waveform transforms a baseband message signal into a passband signal. A
modulator is a device that performs modulation. A
demodulator is a device that performs
demodulation, the inverse of modulation. A modem can perform both operations. The aim of
digital modulation is to transfer a digital bit stream over an analog bandpass channel, for example over the public switched telephone network, or over a limited radio frequency band. The aim of
analog modulation is to transfer an analog baseband signal, for example an audio signal or TV signal, over an analog bandpass channel at a different frequency, for example over a limited radio frequency band or a cable TV network channel.