Clipping is a form of
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 s ...
that limits a
signal
In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The '' IEEE Transactions on Signal Processing' ...
once it exceeds a threshold. Clipping may occur when a signal is recorded by a
sensor that has constraints on the range of data it can measure, it can occur when a signal is
digitized
DigitizationTech Target. (2011, April). Definition: digitization. ''WhatIs.com''. Retrieved December 15, 2021, from https://whatis.techtarget.com/definition/digitization is the process of converting information into a digital (i.e. computer-r ...
, or it can occur any other time an
analog
Analog or analogue may refer to:
Computing and electronics
* Analog signal, in which information is encoded in a continuous variable
** Analog device, an apparatus that operates on analog signals
*** Analog electronics, circuits which use analo ...
or
digital signal is transformed, particularly in the presence of
gain
Gain or GAIN may refer to:
Science and technology
* Gain (electronics), an electronics and signal processing term
* Antenna gain
* Gain (laser), the amplification involved in laser emission
* Gain (projection screens)
* Information gain in d ...
or
overshoot and undershoot.
Clipping may be described as hard, in cases where the signal is strictly limited at the threshold, producing a flat cutoff; or it may be described as soft, in cases where the clipped signal continues to follow the original at a reduced gain. Hard clipping results in many high-frequency
harmonics; soft clipping results in fewer higher-order harmonics and intermodulation distortion components.
Audio
In the
frequency domain
In physics, electronics, control systems engineering, and statistics, the frequency domain refers to the analysis of mathematical functions or signals with respect to frequency, rather than time. Put simply, a time-domain graph shows how a ...
, clipping produces strong harmonics in the high-frequency range (as the clipped waveform comes closer to a
squarewave). The extra high-frequency weighting of the signal could make
tweeter damage more likely than if the signal was not clipped.
Many
electric guitar
An electric guitar is a guitar that requires external amplification in order to be heard at typical performance volumes, unlike a standard acoustic guitar (however combinations of the two - a semi-acoustic guitar and an electric acoustic gu ...
players
Players may refer to:
Art, entertainment, and media
* ''Players'' (1979 film), a film starring Ali MacGraw
* ''Players'' (2012 film), a Bollywood film
* ''Players'' (Dicks novel), a novel by Terrance Dicks, based on the television series ''Doc ...
intentionally overdrive their amplifiers (or insert a "fuzz box") to cause clipping in order to get a desired sound (see
guitar distortion).
In general, the distortion associated with clipping is unwanted, and is visible on an
oscilloscope even if it is inaudible.
Images
In the image domain, clipping is seen as
desaturated (washed-out) bright areas that turn to pure white if all
color components clip. In digital colour photography, it is also possible for individual colour channels to clip, which results in inaccurate colour reproduction.
Causes
Analog circuitry
A circuit designer may intentionally use a
clipper
A clipper was a type of mid-19th-century merchant sailing vessel, designed for speed. Clippers were generally narrow for their length, small by later 19th century standards, could carry limited bulk freight, and had a large total sail area. "Cl ...
or
clamper to keep a signal within a desired range.
When an amplifier is pushed to create a signal with more power than it can support, it will amplify the signal only up to its maximum capacity, at which point the signal will be amplified no further.
*An
integrated circuit or discrete
solid state
Solid state, or solid matter, is one of the four fundamental states of matter.
Solid state may also refer to:
Electronics
* Solid-state electronics, circuits built of solid materials
* Solid state ionics, study of ionic conductors and their u ...
amplifier cannot give an output voltage larger than the voltage it is powered by (commonly a 24- or 30-volt spread for operational amplifiers used in
line-level equipment).
*A
vacuum tube
A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied.
The type kn ...
can only move a limited number of
electrons
The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary partic ...
in an amount of time, dependent on its size, temperature, and metals.
*A
transformer
A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
(most commonly used between stages in tube equipment) will clip when its
ferromagnetic
Ferromagnetism is a property of certain materials (such as iron) which results in a large observed magnetic permeability, and in many cases a large magnetic coercivity allowing the material to form a permanent magnet. Ferromagnetic materials ...
core becomes
electromagnetically saturated.
Digital processing
In
digital signal processing
Digital signal processing (DSP) is the use of digital processing, such as by computers or more specialized digital signal processors, to perform a wide variety of signal processing operations. The digital signals processed in this manner ar ...
, clipping occurs when the signal is restricted by the range of a chosen representation. For example in a system using 16-bit
signed integers, 32767 is the largest positive value that can be represented, and if during processing the amplitude of the signal is doubled,
sample values of 32000 should become 64000, but instead they are truncated to the maximum, 32767. Clipping is preferable to the alternative in digital systems — wrapping — which occurs if the
digital hardware is allowed to "
overflow", ignoring the
most significant bit
In computing, bit numbering is the convention used to identify the bit positions in a binary number.
Bit significance and indexing
In computing, the least significant bit (LSB) is the bit position in a binary integer representing the binary ...
s of the magnitude, and sometimes even the sign of the sample value, resulting in gross distortion of the signal.
The incidence of clipping may be greatly reduced by using
floating point numbers instead of integers. However, floating point numbers are usually less efficient to use, sometimes result in a loss of
precision, and they can still clip if a number is extremely large or small.
Avoiding clipping
Clipping can be detected by viewing the signal (on an oscilloscope, for example), and observing that the tops and bottoms of waves aren't smooth anymore. When working with images, some tools can highlight all
pixel
In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device.
In most digital display devices, pixels are the s ...
s that are pure white, allowing the user to identify larger groups of white pixels and decide if too much clipping has occurred.
To avoid clipping, the signal can be dynamically reduced using a
limiter. If not done carefully, this can still cause undesirable distortion, but it prevents any data from being completely lost.
Repairing a clipped signal
When clipping occurs, part of the original signal is lost, so perfect restoration is impossible. Thus, it is much preferable to avoid clipping in the first place. However, when repair is the only option, the goal is to make up a plausible replacement for the clipped part of the signal.
See also
*
Dynamic range
*
Dynamic range compression
Dynamic range compression (DRC) or simply compression is an audio signal processing operation that reduces the volume of loud sounds or amplifies quiet sounds, thus reducing or ''compressing'' an audio signal's dynamic range. Compression is ...
References
{{reflist
Signal processing