A distortion is the alteration of the original shape (or other characteristic) of an object, image, sound, waveform or other form of information or representation. Distortion is usually unwanted, and often many methods are employed to minimize it in practice. In some fields, however, distortion may be desirable; such is the case with electric guitar distortion.
The addition of noise or other extraneous signals (hum, interference) is not considered to be distortion, though the effects of quantization distortion are sometimes considered noise. A quality measure that explicitly reflects both the noise and the distortion is the Signal-to-noise-and-distortion (SINAD) ratio.
- y(t) = F(x(t))
the output is undistorted. Distortion occurs when the transfer function F is more complicated than this. If F is a linear function, for instance a filter whose gain and/or delay varies with frequency, then the signal will experience linear distortion. Linear distortion will not change the shape of a single sinuosoid, but will usually change the shape of a multi-tone signal.
- The first trace (in black) shows the input. It also shows the output from a non-distorting transfer function (straight line).
- A high-pass filter (green trace) will distort the shape of a square wave by reducing its low frequency components. This is the cause of the "droop" seen on the top of the pulses. This "pulse distortion" can be very significant when a train of pulses must pass through an AC-coupled (high-pass filtered) amplifier. As the sine wave contains only one frequency, its shape is unaltered.
- A low-pass filter (blue trace) will round the pulses by removing the high frequency components. All systems are low pass to some extent. Note that the phase of the sine wave is different for the lowpass and the highpass cases, due to the phase distortion of the filters.
- A slightly non-linear transfer function (purple), this one is gently compressing as may be typical of a tube audio amplifier, will compress the peaks of the sine wave. This will cause small amounts of low order harmonics to be generated.
- A hard-clipping transfer function (red) will generate high order harmonics. Parts of the transfer function are flat, which indicates that all information about the input signal has been lost in this region.
The transfer function of an ideal amplifier, with perfect gain and delay, is only an approximation. The true behavior of the system is usually different. Nonlinearities in the transfer function of an active device (such as vacuum tubes, transistors, and operational amplifiers) are a common source of non-linear distortion; in passive components (such as a coaxial cable or optical fiber), linear distortion can be caused by inhomogeneities, reflections, and so on in the propagation path.
Harmonic distortion adds overtones that are whole number multiples of a sound wave's frequencies. Nonlinearities that give rise to amplitude distortion in audio systems are most often measured in terms of the harmonics (overtones) added to a pure sinewave fed to the system. Harmonic distortion may be expressed in terms of the relative strength of individual components, in decibels, or the Root Mean Square of all harmonic components: Total harmonic distortion (THD), as a percentage. The level at which harmonic distortion becomes audible is not straightforward. Different types of distortion (like crossover distortion) are more audible than others (like soft clipping) even if the THD measurements are identical. Harmonic distortion in RF applications is rarely expressed as THD.
Frequency response distortion
Non-flat frequency response is a form of distortion that occurs when different frequencies are amplified by different amounts, caused by filters. For example, the non-uniform frequency response curve of AC-coupled cascade amplifier is an example of frequency distortion. In the audio case, this is mainly caused by room acoustics, poor loudspeakers and microphones, long loudspeaker cables in combination with frequency dependent loudspeaker impedance, etc.
This form of distortion mostly occurs due to the reactive component, such as capacitive reactance or inductive reactance. Here, all the components of the input signal are not amplified with the same phase shift, hence causing some parts of the output signal to be out of phase with the rest of the output.
Group delay distortion
Can be found only in dispersive media. In a waveguide, propagation velocity varies with frequency. In a filter, group delay tends to peak near the cut-off frequency, resulting in pulse distortion. When analog long distance trunks were commonplace, for example in 12 channel carrier, group delay distortion had to be corrected in repeaters.
Correction of distortion
As the system output is given by y(t) = F(x(t)), then if the inverse function F−1 can be found, and used intentionally to distort either the input or the output of the system, then the distortion will be corrected.
An example of such correction is where LP/vinyl recordings or FM audio transmissions are deliberately pre-emphasised by a linear filter, the reproducing system applies an inverse filter to make the overall system undistorted.
Correction is not possible if the inverse does not exist, for instance if the transfer function has flat spots (the inverse would map multiple input points to a single output point). This results in a loss of information, which is uncorrectable. Such a situation can occur when an amplifier is overdriven, resulting in clipping or slew rate distortion, when for a moment the output is determined by the characteristics of the amplifier alone, and not by the input signal.
Teletypewriter or modem signaling
In binary signaling such as FSK, distortion is the shifting of the significant instants of the signal pulses from their proper positions relative to the beginning of the start pulse. The magnitude of the distortion is expressed in percent of an ideal unit pulse length. This is sometimes called 'bias' distortion.
Telegraphic distortion is a similar older problem, distorting the ratio between "mark" and "space" intervals. 
In this context, distortion refers to any kind of deformation of a waveform, compared to an input, usually Clipping, harmonic distortion and intermodulation distortion (mixing phenomena) caused by non-linear behavior of electronic components and power supply limitations. Terms for specific types of nonlinear audio distortion include: crossover distortion, slew-Induced Distortion (SID) and transient intermodulation (TIM).
Distortion in music is sometimes intentionally used as an effect, see also overdrive and distortion synthesis. Other forms of audio distortion that may be referred to are non-flat frequency response, compression, modulation, aliasing, quantization noise, wow and flutter from analog media such as vinyl records and magnetic tape. The human ear cannot hear phase distortion, except that it may affect the stereo imaging. (See also: Audio system measurements.)
In most fields, distortion is characterized as unwanted change to a signal.
- Amplitude distortion
- Attenuation distortion
- Bias distortion
- Crossover distortion
- Degree of isochronous distortion
- Degree of start-stop distortion
- Delay distortion
- Distortion-limited operation
- Distortion (music)
- Distortion power factor
- Frequency-selective fading
- Image warping
- Intermodulation distortion
- Lossy compression
- Minimum Resolvable Contrast
- Overdrive (music)
- Total harmonic distortion — a measurement of the amount of distortion in a sinusoidal waveform
- Valve sound
- ^ Moscal, Tony (1994). Sound Check: The Basics of Sound and Sound Systems. Hal Leonard. p. 55. http://books.google.com/books?id=_omgNjqf7GAC&pg=PA55&dq=harmonic+distortion+whole+integer#v=onepage&q&f=false.
- ^ Audio Electronics by John Linsley Hood; page 162
Noise (in physics and telecommunications) General Noise in... Class of noise Engineering terms RatiosCarrier-to-noise ratio (C/N) · Carrier-to-receiver noise density (C/kT) · dBrnC · Eb/N0 (energy per bit to noise density) · Es/N0 (energy per symbol to noise density) · Modulation error ratio (MER) · Signal, noise and distortion (SINAD) · Signal-to-interference ratio (S/I) · Signal-to-noise ratio (S/N, SNR) · Signal to noise ratio (imaging) · Signal-to-noise plus interference (SNIR) · Signal-to-quantization-noise ratio (SQNR) Related topics Analogue television broadcasting topics Systems Color systems VideoBack porch and front porch • Black level • Chrominance • Chrominance subcarrier • Colorburst • Color killer • Color TV • Composite video • Frame (video) • Horizontal scan rate • Horizontal blanking interval • Luma • Nominal analogue blanking • Overscan • Raster scan • Safe area • Television lines • Vertical blanking interval • White clipper Sound Modulation TransmissionAmplifiers • Antenna (radio) • Cavity amplifier • Differential gain • Differential phase • Diplexer • Dipole antenna • Dummy load • Frequency mixer • Intercarrier method • Intermediate frequency • Output power of an analog TV transmitter • Pre-emphasis • Residual carrier • Split sound system • Superheterodyne transmitter • Television receive-only • Television transmitter • Terrestrial television • Transmitter station • Transposer Frequencies & Bands Propagation Testing Artifacts
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Look at other dictionaries:
Distortion — Dis*tor tion, n. [L. distortio: cf. F. distortion.] 1. The act of distorting, or twisting out of natural or regular shape; a twisting or writhing motion; as, the distortions of the face or body. [1913 Webster] 2. A wresting from the true meaning … The Collaborative International Dictionary of English
Distortion — (lat./engl. für ‚Störung, Verzerrung‘) steht: in der Nachrichtentechnik die ungewünschte Verfälschung eines Signals durch einen Verstärker, siehe Verzerrung (Akustik) in der Musik ein Effektgerät, siehe Verzerrer Siehe auch: Verzerrung Distorsion … Deutsch Wikipedia
Distortion — Distortion. См. Коробление. (Источник: «Металлы и сплавы. Справочник.» Под редакцией Ю.П. Солнцева; НПО Профессионал , НПО Мир и семья ; Санкт Петербург, 2003 г.) … Словарь металлургических терминов
distortion — I noun anamorphosis, camouflage, caricature, contortion, convolution, deception, deformation, deformity, disguise, disparity, disproportion, dissemblance, dissimilarity, dissimilitude, distortio, embroidery, enlargement, exaggeration, expansion,… … Law dictionary
distortion — 1580s, action of distorting, from L. distortionem (nom. distortio), noun of action from pp. stem of distorquere (see DISTORT (Cf. distort)). Figurative use (of words, etc.) from 1640s … Etymology dictionary
distortion — [n] deformity; falsification baloney*, bend, bias, BS*, buckle, coloring, contortion, crock, crookedness, exaggeration, intorsion, jazz*, jive*, lie, line, malconformation, malformation, misinterpretation, misrepresentation, misshape,… … New thesaurus
distortion — [di stôr′shən] n. [L distortio] 1. a distorting or being distorted 2. anything distorted distortional adj … English World dictionary
distortion — distortional, distortionary, adj. /di stawr sheuhn/, n. 1. an act or instance of distorting. 2. the state of being distorted or the relative degree or amount by which something is distorted or distorts. 3. anything that is distorted, as a sound,… … Universalium
Distortion — (Roget s Thesaurus) >Irregularity of form. < N PARAG:Distortion >N GRP: N 1 Sgm: N 1 distortion distortion detortion contortion Sgm: N 1 twist twist crookedness &c.(obliquity) 217 Sgm: N 1 grimace grimace Sgm: N 1 deformity … English dictionary for students
distortion — noun 1 change in shape/sound ADJECTIVE ▪ severe ▪ slight ▪ inevitable ▪ image VERB + DISTORTION ▪ … Collocations dictionary