Editing Frequency-division multiplexing (section)

== Other examples ==
FDM can also be used to combine signals before final modulation onto a carrier wave. In this case the [[carrier signal]]s are referred to as [[subcarrier]]s: an example is [[stereo FM]] transmission, where a 38&nbsp;kHz subcarrier is used to separate the left-right difference signal from the central left-right sum channel, prior to the frequency modulation of the composite signal.
An analog [[NTSC]] television channel is divided into [[subcarrier#Television|subcarrier frequencies]] for video, color, and audio.
DSL uses different frequencies for voice and for [[upstream (networking)|upstream]] and [[downstream (computer science)|downstream]] data transmission on the same conductors, which is also an example of [[frequency duplex]].
	 
Where frequency-division multiplexing is used as to allow multiple users to share a physical [[communications channel]], it is called [[frequency-division multiple access]] (FDMA).<ref>
{{cite book | last = White | first = Curt | year = 2007 | title = Data Communications and Computer Networks | publisher = Thomson Course Technology | location = Boston, MA | pages = [https://archive.org/details/datacommunicatio00whit_0/page/140 140–143] | isbn = 978-1-4188-3610-8 | url-access = registration | url = https://archive.org/details/datacommunicatio00whit_0/page/140 }}
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FDMA is the traditional way of separating [[radio]] signals from different
transmitters.
	 
In the 1860s and 70s, several inventors attempted FDM under the names of [[acoustic telegraphy]] and harmonic telegraphy. Practical FDM was only achieved in the electronic age. Meanwhile, their efforts led to an elementary understanding of electroacoustic technology, resulting in the [[invention of the telephone]].