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In [[electronics]] and [[telecommunications]], '''modulation''' is the process of varying one or more properties of a periodic [[waveform]], called the ''[[carrier signal]]'', with a separate signal called the ''modulation signal'' that typically contains information to be transmitted.{{Citation needed|date=March 2023}} For example, the modulation signal might be an [[audio signal]] representing [[sound]] from a [[microphone]], a [[video signal]] representing moving images from a [[video camera]], or a [[digital signal]] representing a sequence of binary digits, a [[bitstream]] from a computer.
This carrier wave usually has a much higher [[frequency]] than the message signal does. This is because it is impractical to transmit signals with low frequencies. Generally, to receive a [[radio wave]] one needs a [[Antenna (radio)|radio antenna]] with length of one fourth of
Another purpose of modulation is to transmit multiple channels of information through a single communication medium, using [[frequency-division multiplexing]] (FDM). For example, in [[cable television]] (which uses FDM), many carrier signals, each modulated with a different [[television channel]], are transported through a single cable to customers. Since each carrier occupies a different frequency, the channels do not interfere with each other. At the destination end, the carrier signal is [[demodulation|demodulated]] to extract the information bearing modulation signal.
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