Editing Bandwidth (signal processing) (section)

{{Short description|Range of usable frequencies}}
{{about|the concept in signal theory and processing measured in hertz|use in computing and networking expressed in bits per second|Bandwidth (computing)|other uses|Bandwidth (disambiguation)}}

[[Image:Baseband.svg|right|300px|thumb|Amplitude (a) vs. frequency (f) graph illustrating [[baseband]] bandwidth. Here the bandwidth equals the upper frequency.]]

'''Bandwidth''' is the difference between the upper and lower [[Frequency|frequencies]] in a continuous [[Frequency band|band of frequencies]].  It is typically measured in [[unit of measurement|unit]] of [[hertz]] (symbol Hz).

It may refer more specifically to two subcategories: ''[[Passband]] bandwidth'' is the difference between the upper and lower [[cutoff frequencies]] of, for example, a [[band-pass filter]], a [[communication channel]], or a [[signal spectrum]]. ''[[Baseband]] bandwidth'' is equal to the upper cutoff frequency of a [[low-pass filter]] or baseband signal, which includes a zero frequency.

Bandwidth in hertz is a central concept in many fields, including [[electronics]], [[information theory]], [[digital communication]]s, [[radio communication]]s, [[signal processing]], and [[spectroscopy]] and is one of the determinants of the capacity of a given [[communication channel]].

A key characteristic of bandwidth is that any band of a given width can carry the same amount of [[information]], regardless of where that band is located in the [[frequency spectrum]].{{efn|The information capacity of a channel depends on [[Noise (electronics)|noise]] level as well as bandwidth – see [[Shannon–Hartley theorem]]. Equal bandwidths can carry equal information only when subject to equal [[signal-to-noise ratio]]s.}} For example, a 3&nbsp;kHz band can carry a telephone conversation whether that band is at baseband (as in a [[plain old telephone service|POTS]] telephone line) or [[modulated]] to some higher frequency.  However, wide bandwidths are easier to obtain and [[signal processing|process]] at higher frequencies because the {{section link|#Fractional bandwidth}} is smaller.