Distortion

In

, such that the output ${\displaystyle y(t)}$ can be written as a function of the input ${\displaystyle x}$ as

${\displaystyle y(t)=F(x(t))}$

When the transfer function comprises only a perfect gain constant A and perfect delay T

${\displaystyle y(t)=A\cdot x(t-T)}$

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, the signal suffers linear distortion. Linear distortion does not introduce new frequency components to a signal but does alter the balance of existing ones.

This diagram shows the behaviour of a signal (made up of a square wave followed by a sine wave) as it is passed through various distorting functions.

1. The first trace (in black) shows the input. It also shows the output from a non-distorting transfer function (straight line).
2. A high-pass filter (green trace) distorts 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.
3. A low-pass filter (blue trace) rounds 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.
4. A slightly
   tube audio amplifier
   . This generates small amounts of low order harmonics.
5. A hard-clipping transfer function (red) generates 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.

Amplitude distortion

Amplitude distortion is distortion occurring in a system, subsystem, or device when the output amplitude is not a linear function of the input amplitude under specified conditions.

Harmonic distortion

Harmonic distortion adds

Non-flat frequency response is a form of distortion that occurs when different frequencies are amplified by different amounts in a

This form of distortion mostly occurs due to electrical reactance. Here, all the components of the input signal are not amplified with the same phase shift, hence making some parts of the output signal out of phase with the rest of the output.

Group delay distortion

Can be found only in

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 produces an uncorrectable loss of information. Such a situation can occur when an amplifier is overdriven—causing clipping or slew rate distortion when, for a moment, the amplifier characteristics alone and not the input signal determine the output.

Cancellation of even-order harmonic distortion

Many symmetrical

Teletypewriter or modem signaling

In binary

Telegraphic distortion is a similar and older problem, distorting the ratio between mark and space intervals.^[2]

Audio distortion

Distorted waveforms

An audio example of a short sample followed by different distorted versions of it.

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With respect to audio, distortion refers to any kind of deformation of an output waveform compared to its input, usually

In most fields, distortion is characterized as unwanted change to a signal. Distortion in music is often intentionally used as an effect when applied to an electric guitar signal in styles of rock music such as heavy metal and punk rock.

Distortion in art

In the art world, a distortion is any change made by an artist to the size, shape or visual character of a form in order to express an idea, convey a feeling, or enhance visual impact. Such distortions or "abstractions" primarily refer to purposeful deviations from

In

In cartography, a distortion is the misrepresentation of the area or shape of a feature. The Mercator projection, for example, distorts by exaggerating the size of regions at high latitude.

See also

References