Clipping (signal processing)

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An oscilloscope screen of an amplifier clipping. The amplifier should be outputting a clean sine wave with rounded tops and bottoms, but instead they are cut off flat, or clipped.

Clipping is a form of

digitized, or it can occur any other time an analog or digital signal is transformed, particularly in the presence of gain 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

This PCM waveform is clipped between the red lines
Main article: Clipping (audio)

In the frequency domain, clipping produces strong harmonics in the high-frequency range (as the clipped waveform comes closer to a square wave). The extra high-frequency weighting of the signal could make tweeter damage more likely than if the signal was not clipped.

Many electric guitar players 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.[1]

Images

Main article: Clipping (photography)
Example image exhibiting blown-out highlights. Top: original image, bottom: blown-out areas marked red

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 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
    line-level
    equipment).
  • A
    electrons
    in an amount of time, dependent on its size, temperature, and metals.
  • A
    ferromagnetic core becomes electromagnetically saturated
    .

Digital processing

Further information: Saturation arithmetic

In

most significant bits
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 pixels 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

References

  1. ISBN 0-933224-97-4
    .
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