Attenuation distortion is the
distortion
In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signal ...
of an
analog signal
An analog signal (American English) or analogue signal (British and Commonwealth English) is any continuous-time signal representing some other quantity, i.e., ''analogous'' to another quantity. For example, in an analog audio signal, the ins ...
that occurs during
transmission when the
transmission medium
A transmission medium is a system or substance that can mediate the propagation of signals for the purposes of telecommunication. Signals are typically imposed on a wave of some kind suitable for the chosen medium. For example, data can modula ...
does not have a flat
frequency response
In signal processing and electronics, the frequency response of a system is the quantitative measure of the magnitude and Phase (waves), phase of the output as a function of input frequency. The frequency response is widely used in the design and ...
across the
bandwidth of the medium or the
frequency spectrum
In signal processing, the power spectrum S_(f) of a continuous time signal x(t) describes the distribution of power into frequency components f composing that signal. According to Fourier analysis, any physical signal can be decomposed int ...
of the signal.
[Rowe, Standord H. II, ''Network Technology & Service Integration'' (5th Edition), 2002, Prentice-Hall, Inc., 2002]
Attenuation distortion occurs when some
frequencies are
attenuated more than other frequencies. When an analog signal of constant
amplitude
The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of am ...
across its frequency spectrum suffers attenuation distortion, some frequencies of the received signal arrive being greater in amplitude (louder), relative to other frequencies.
To overcome the effects of attenuation distortion,
communications circuits have special
equalization equipment attached at the ends of the circuit or in between, designed to attenuate the signal evenly across the frequency spectrum, or to allow the signal to be received at equal amplitude for all frequencies. Attenuation distortion can still occur in a properly equipped circuit if this equalization filter is not properly maintained or adjusted.
In
DSL
Digital subscriber line (DSL; originally digital subscriber loop) is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is widely understood to mean asymmetric di ...
circuits,
echoes due to
impedance mismatch often cause attenuation distortion so severe that some frequencies must be automatically mapped out and not used.
References
{{telcom-stub
Telecommunications