
Clipping is a form of
waveform
In electronics, acoustics, and related fields, the waveform of a signal is the shape of its Graph of a function, graph as a function of time, independent of its time and Magnitude (mathematics), magnitude Scale (ratio), scales and of any dis ...
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 ...
that occurs when an
amplifier
An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It is a two-port electronic circuit that uses electric power from a power su ...
is overdriven and attempts to deliver an output voltage or current beyond its maximum capability. Driving an amplifier into clipping may cause it to output power in excess of its
power rating
In electrical engineering and mechanical engineering, the power rating of equipment is the highest power input allowed to flow through particular equipment. According to the particular discipline, the term ''power'' may refer to electrical or ...
.
In the
frequency domain
In mathematics, physics, electronics, control systems engineering, and statistics, the frequency domain refers to the analysis of mathematical functions or signals with respect to frequency (and possibly phase), rather than time, as in time ser ...
, clipping produces strong
harmonic
In physics, acoustics, and telecommunications, a harmonic is a sinusoidal wave with a frequency that is a positive integer multiple of the ''fundamental frequency'' of a periodic signal. The fundamental frequency is also called the ''1st har ...
s in the high-frequency range (as the clipped waveform comes closer to a
square wave Square wave may refer to:
*Square wave (waveform)
A square wave is a non-sinusoidal waveform, non-sinusoidal periodic waveform in which the amplitude alternates at a steady frequency between fixed minimum and maximum values, with the same ...
). The extra high-frequency weighting of the signal could make
tweeter
A tweeter or treble speaker is a special type of loudspeaker (usually dome, inverse dome or horn-type) that is designed to produce high audio frequencies, typically from 2,000 to 20,000 Hertz, Hz. The name is derived from the high pitched sound ...
damage more likely than if the signal was not clipped.
In most cases, the distortion associated with clipping is unwanted, and is visible on an
oscilloscope
An oscilloscope (formerly known as an oscillograph, informally scope or O-scope) is a type of electronic test instrument that graphically displays varying voltages of one or more signals as a function of time. Their main purpose is capturing i ...
even if it is inaudible. However, clipping is often used in music for artistic effect, particularly guitar-dominant genres like blues, rock, and metal.
Overview
When an amplifier is pushed to create a signal with more power than its power supply can produce, it will amplify the signal only up to its maximum capacity, at which point the signal can be amplified no further. As the signal simply "cuts" or "clips" at the maximum capacity of the amplifier, the signal is said to be "clipping". The extra signal which is beyond the capability of the amplifier is simply cut off, resulting in a
sine wave
A sine wave, sinusoidal wave, or sinusoid (symbol: ∿) is a periodic function, periodic wave whose waveform (shape) is the trigonometric function, trigonometric sine, sine function. In mechanics, as a linear motion over time, this is ''simple ...
becoming a distorted
square-wave-type waveform.
Amplifiers have voltage, current and thermal limits. Clipping may occur due to limitations in the power supply or the output stage. Some amplifiers are able to deliver
peak power
''Peak power'' refers to the maximum of the instantaneous power waveform, which, for a sine wave, is always twice the average power. For other waveforms, the relationship between peak power and average power is the peak-to-average power ratio (PAP ...
without clipping for short durations before energy stored in the power supply is depleted or the amplifier begins to overheat.
Sound
Many
electric guitar
An electric guitar is a guitar that requires external electric Guitar amplifier, sound amplification in order to be heard at typical performance volumes, unlike a standard acoustic guitar. It uses one or more pickup (music technology), pickups ...
players intentionally overdrive their amplifiers (or insert a "fuzz box") to cause clipping in order to get a desired sound (see
guitar distortion
Distortion and overdrive are forms of audio signal processing used to alter the sound of amplified electric musical instruments, usually by increasing their gain, producing a "fuzzy", "growling", or "gritty" tone. Distortion is most commonly ...
).
Some
audiophiles
An audiophile (from + ) is a person who is enthusiastic about high-fidelity sound reproduction. The audiophile seeks to achieve high sound quality in the audio reproduction of recorded music, typically in a quiet listening space in a room with g ...
believe that the clipping behavior of
vacuum tube
A vacuum tube, electron tube, thermionic 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. It ...
s with little or no
negative feedback
Negative feedback (or balancing feedback) occurs when some function (Mathematics), function of the output of a system, process, or mechanism is feedback, fed back in a manner that tends to reduce the fluctuations in the output, whether caused ...
is superior to that of
transistors
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...
, in that vacuum tubes clip more gradually than transistors (i.e. ''soft'' clipping, and mostly even harmonics), resulting in harmonic distortion that is generally less objectionable.
Effects
In a transistorized amplifier with hard clipping, the gain of the transistor will be reducing (leading to nonlinear distortion) as the output current increases and the voltage across the transistor reduces close to the saturation voltage (for
bipolar transistors
A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor (FET), uses only one kind of charge carrier. A ...
), and so "full power" for the purposes of measuring distortion in amplifiers is usually taken as a few percent ''below'' clipping.
Because the clipped waveform has more area underneath it than the smaller unclipped waveform, the amplifier produces more
power
Power may refer to:
Common meanings
* Power (physics), meaning "rate of doing work"
** Engine power, the power put out by an engine
** Electric power, a type of energy
* Power (social and political), the ability to influence people or events
Math ...
than its rated (
sine wave
A sine wave, sinusoidal wave, or sinusoid (symbol: ∿) is a periodic function, periodic wave whose waveform (shape) is the trigonometric function, trigonometric sine, sine function. In mechanics, as a linear motion over time, this is ''simple ...
) output when it is clipping. This extra
power
Power may refer to:
Common meanings
* Power (physics), meaning "rate of doing work"
** Engine power, the power put out by an engine
** Electric power, a type of energy
* Power (social and political), the ability to influence people or events
Math ...
can damage the
loudspeaker
A loudspeaker (commonly referred to as a speaker or, more fully, a speaker system) is a combination of one or more speaker drivers, an enclosure, and electrical connections (possibly including a crossover network). The speaker driver is an ...
. It may cause damage to the amplifier's
power supply
A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, electric current, current, and frequency to power ...
or simply blow a
fuse
Fuse or FUSE may refer to:
Devices
* Fuse (electrical), a device used in electrical systems to protect against excessive current
** Fuse (automotive), a class of fuses for vehicles
* Fuse (hydraulic), a device used in hydraulic systems to protec ...
.
The additional high frequency energy in the harmonics generated by an amplifier operating in clipping can damage the
tweeter
A tweeter or treble speaker is a special type of loudspeaker (usually dome, inverse dome or horn-type) that is designed to produce high audio frequencies, typically from 2,000 to 20,000 Hertz, Hz. The name is derived from the high pitched sound ...
in a connected
loudspeaker
A loudspeaker (commonly referred to as a speaker or, more fully, a speaker system) is a combination of one or more speaker drivers, an enclosure, and electrical connections (possibly including a crossover network). The speaker driver is an ...
via overheating.
Clipping can occur within a system as processing (e.g. an
all-pass filter
An all-pass filter is a signal processing filter that passes all frequencies equally in gain, but changes the phase relationship among various frequencies. Most types of filter reduce the amplitude (i.e. the magnitude) of the signal applied to it ...
) can change the phase relationship between spectral components of a signal in such a way as to create excessive peak outputs. The excessive peaks may become clipped even though the system can play any simple sine wave signals of the same level without clipping.
Electric guitar
An electric guitar is a guitar that requires external electric Guitar amplifier, sound amplification in order to be heard at typical performance volumes, unlike a standard acoustic guitar. It uses one or more pickup (music technology), pickups ...
ists frequently and intentionally overdrive their
guitar amplifier
A guitar amplifier (or amp) is an electronic amplifier, electronic device or system that strengthens the electrical signal from a Pickup (music technology), pickup on an electric guitar, bass guitar, or acoustic guitar so that it can produce so ...
s to cause clipping and other
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 ...
in order to get a desired sound.
Digital clipping

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 are a ...
, 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. If, during processing, the amplitude of the signal is doubled,
sample
Sample or samples may refer to:
* Sample (graphics), an intersection of a color channel and a pixel
* Sample (material), a specimen or small quantity of something
* Sample (signal), a digital discrete sample of a continuous analog signal
* Sample ...
values of, for instance, 32000 should become 64000, but instead cause an
integer overflow
In computer programming, an integer overflow occurs when an arithmetic operation on integers attempts to create a numeric value that is outside of the range that can be represented with a given number of digits – either higher than the maximu ...
and
saturate
Saturate may refer to:
* ''Saturate'' (Breaking Benjamin album), 2002
* ''Saturate'' (Gojira album), 1999
* ''Saturate'' (Jeff Deyo album), 2002
* " Electronic Battle Weapon 8", a song by The Chemical Brothers, a shorter version of which was re ...
to the maximum, 32767. Clipping is preferable to the alternative in digital systems—wrapping—which occurs if the digital processor 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 numeral system, binary number.
Bit significance and indexing
In computing, the least significant bit (LSb) is the bit position in a Binary numeral sy ...
s of the magnitude, and sometimes even the sign of the sample value, resulting in gross distortion of the signal.
Avoiding clipping
The simplest way to avoid clipping is to reduce the signal level. Alternatively the system can be improved to support higher signal level without clipping. Some audiophiles will use amplifiers that are rated for power outputs over twice the speaker's ratings. A
limiter
In electronics, a limiter is a circuit that allows signals below a specified input power or level to pass unaffected while attenuating (lowering) the peaks of stronger signals that exceed this threshold. Limiting is a type of dynamic range co ...
can be used to dynamically bring the levels of the loud parts of a signal down (for example,
bass
Bass or Basses may refer to:
Fish
* Bass (fish), various saltwater and freshwater species
Wood
* Bass or basswood, the wood of the tilia americana tree
Music
* Bass (sound), describing low-frequency sound or one of several instruments in th ...
and
snare drum
The snare drum (or side drum) is a percussion instrument that produces a sharp staccato sound when the head is struck with a drum stick, due to the use of a series of stiff wires held under tension against the lower skin. Snare drums are often u ...
s).
Many amplifier designers have incorporated circuits to prevent clipping. The simplest circuits act like a fast limiter, which engages about one decibel before the clipping point. A more complex circuit, called "soft-clip", has been used from the 1980s onward to limit the signal at the input stage. The soft-clip feature begins to engage prior to clipping, for instance starting at 10 dB below maximum output power. The output waveform retains a rounded characteristic even in the presence of an overload input signal as much as 10 dB higher than maximum specified.
Repairing a clipped signal
It is preferable to avoid clipping, but if a recording has clipped, and cannot be re-recorded, repair is an option. The goal of repair is to make up a plausible replacement for the clipped part of the signal.
Complex hard-clipped signals cannot be restored to their original state because the information contained in the peaks that are clipped is completely lost. Soft-clipped signals can be restored to their original state to within a case-dependent tolerance because no part of the original signal is completely lost. In this case, the degree of information loss is proportional to the degree of compression caused by the clipping. Lightly clipped bandwidth-limited signals that are highly oversampled have the potential for perfect repair.
Several methods can partially restore a clipped signal. Once the clipped portion is known, one can attempt partial recovery. One such method is
interpolation
In the mathematics, mathematical field of numerical analysis, interpolation is a type of estimation, a method of constructing (finding) new data points based on the range of a discrete set of known data points.
In engineering and science, one ...
or
extrapolation
In mathematics
Mathematics is a field of study that discovers and organizes methods, Mathematical theory, theories and theorems that are developed and Mathematical proof, proved for the needs of empirical sciences and mathematics itself. ...
of known samples. Advanced implementations may use
cubic splines to attempt to restore a
continuously differentiable
In mathematics, a differentiable function of one Real number, real variable is a Function (mathematics), function whose derivative exists at each point in its Domain of a function, domain. In other words, the Graph of a function, graph of a differ ...
signal. While these reconstructions are only an approximation of the original, the subjective quality may be improved. Other methods include copying the signal directly from one stereo channel to another, as it may be the case that only one channel is clipped.
Several software solutions of varying results and methods exist to repair clipping: CrumplePop ClipRemover, MAGIX
Sound Forge
Sound Forge (formerly known as Sonic Foundry Sound Forge, and later as Sony Sound Forge) is a digital audio editing suite by Magix, which is aimed at the professional and semi-professional markets. There are two versions of Sound Forge: Sound For ...
,
iZotope
iZotope, Inc. is an audio technology company based in Cambridge, Massachusetts, Cambridge, Massachusetts, United States. iZotope develops professional audio software for audio recording, mixing, broadcast, sound design, and mastering which can ...
RX De-Clip,
Acon Digital Restoration Suite,
Adobe Audition
Adobe Audition is a digital audio workstation developed by Adobe Inc. featuring both a multitrack, non-destructive mix/edit environment and a destructive-approach waveform editing view.
Origins
Syntrillium Software was founded in the early 1 ...
, Thimeo Stereo Tool, declipping solutions from CEDAR Audio, and
Audacity plugins such as Clip Fix.
Causes
In
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 analog ...
audio equipment, there are several causes of clipping:
# The peak-to-peak output of a solid-state transformerless amplifier is limited by the
power supply
A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, electric current, current, and frequency to power ...
voltage.
# An amplifier may have an asymmetrical output swing and clipping may begin earlier on one half of the output waveform.
# In audio amplifiers using unregulated linear power supplies, if the
filter capacitor
Capacitors have many uses in electronic and electrical systems. They are so ubiquitous that it is rare that an electrical product does not include at least one for some purpose. Capacitors allow only AC signals to pass when they are charged blocki ...
is not large enough, it is possible for
ripple voltage
Ripple (specifically ripple voltage) in electronics is the residual periodic variation of the DC voltage within a power supply which has been derived from an alternating current (AC) source. This ripple is due to incomplete suppression of the al ...
to cause clipping that also contains some AC line frequency harmonics. In a
switched-mode power supply
A switched-mode power supply (SMPS), also called switching-mode power supply, switch-mode power supply, switched power supply, or simply switcher, is an electronic power supply that incorporates a switching regulator to electric power conversio ...
the switching frequency is more dominant in the ripple voltage and outside the
audio band while in a
regulated power supply
A regulated power supply is an embedded circuit; it converts unregulated AC (alternating current) into a constant DC. With the help of a rectifier it converts AC supply into DC. Its function is to supply a stable voltage (or less often current), to ...
the ripple voltage is rejected.
# A
vacuum tube
A vacuum tube, electron tube, thermionic 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. It ...
can only move a limited number of
electrons
The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...
in a given amount of time, dependent on its size, temperature, and metals. The resulting fall-off in amplification with increasing output current results in ''soft clipping''.
# Amplifying devices may also have limits on their inputs, for example excessive base current to a bipolar transistor or excessive grid current to a
vacuum tube
A vacuum tube, electron tube, thermionic 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. It ...
. Operating outside these limits can distort the input signal, if it comes from a high enough
impedance source, or damage the amplifying device requiring a limiting circuit for protection; see below.
# An amplifier may limit its current output, or the input voltage, for a variety of reasons both intentional or not. Intentional limiting circuits would not be expected to come into effect in normal operation, but only when the output load
resistance is too low or the input signal level is exceptionally high, for example. The result of this form of clipping might not create a flat top to the voltage waveform, but rather a flat top to the current waveform.
# A transformer (most commonly used between stages and at the output in tube equipment) will clip when its
ferromagnetic
Ferromagnetism is a property of certain materials (such as iron) that results in a significant, observable magnetic permeability, and in many cases, a significant magnetic coercivity, allowing the material to form a permanent magnet. Ferromagne ...
core becomes
electromagnetically saturated.
Detection
Clipping in a circuit can be detected by comparing the original input signal with an output signal with adjustment for applied gain. For instance, if a circuit has 10 dB of applied gain, it can be tested for clipping by attenuating the output signal by 10 dB and comparing it to the input signal. The difference between the two signals can be used to illuminate clipping detection indicators and can be used to decrease the gain of a preceding circuit to manage clipping.
Clipped signals will often be squarized, where third harmonics are contextual outliers in a Fourier Transform. In the case of an expected sine wave, the presence of odd harmonics will often suggest the signal has been hard clipped. A “soft clip” will have a knee on both sides of the plateau, which will show the presence of several even overtones in the lower frequency spectrum.
See also
*
Clipper (electronics)
In electronics, a clipper is a circuit designed to prevent a signal from exceeding a predetermined reference voltage level. A clipper does not distort the remaining part of the applied waveform. Clipping circuits are used to select, for purpos ...
*
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 c ...
*
Tube sound
Tube sound (or valve sound) is the characteristic sound associated with a vacuum tube amplifier (valve amplifier in British English), a vacuum tube-based audio amplifier. At first, the concept of ''tube sound'' did not exist, because practicall ...
Notes
References
{{DEFAULTSORT:Clipping (Audio)
Audio engineering
Sound production technology