Overdrive (signal processing)

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Display of a sine that has been cut off due to overload on an oscilloscope

In signal processing, overdriving is the application of input signals outside the permitted input range to signal processing units. As a result of overdriving, undesirable effects such as non-linearities occur . Typically, excursions that extend beyond the entrance area are cut off. This effect is called limiting or clipping (English to clip = cut off, to cut).

With control loops , override can even lead to complete failure. On the other hand, in many circuits for frequency doubling, overdriving is a prerequisite for the function.

Overdrive in audio amplifiers

Overdrive (English overdrive ) or short drive called, referred to the accidental or deliberate inducing music of a distortion in an electrically transported beep.


Clipping a digital waveform

An amplifier can be due to excessive input level or too high a gain in the saturation occur, in which the output signal is no longer true to form follows the input signal, but is distorted and clipped thereby. The signal curve is "cut off" at the upper and lower signal peaks. Such processes can be visualized in the form of a sine curve, which is flattened at the upper and lower bulges by means of two horizontal straight lines. If a single frequency is fed in, only additional overtones , so-called harmonics , arise in the signal spectrum . If (with music) different frequencies are fed in at the same time, there are always additional combination frequencies, i.e. the sums and differences of the original frequencies, because the amplifier then works as a mixer .

Overloads are usually undesirable; in musical effects devices , however, such an effect is often used deliberately. See Distortion . Guitar amplifiers can, for example, be intentionally overdriven by an excessive input signal in order to distort the instrument signal .

Solid-state amplifiers sound particularly unpleasant when overdriven, while tube amplifiers cause the signal to be more smoothly limited. For this reason, some transistor amplifiers are equipped with so-called soft clipping , which means a softer overload behavior.

Tube amplifiers and tube microphones (triodes), which can generate non-linear distortion with a quadratic THD at higher volumes on an asymmetrical characteristic with only even harmonics , particularly emphasize those partials that are harmonically closely related to the fundamental. In the distortion factor k 2 , k 4 , k 6 etc. they have components of the harmonics.

See also


  • Martin Meyer: Signal processing. Analog and digital signals - systems and filters, 8th edition, Springer Fachmedien, Wiesbaden 2017, ISBN 978-3-658-18320-2 .

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