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In telecommunication and signal processing, the term distortion has the following meanings:

  1. In a system or device, any departure of the output signal waveform from that which should result from the input signal waveform's being operated on by the system's specified, i.e, ideal, transfer function.

    Distortion may result from many mechanisms. Examples include nonlinearities in the transfer function of an active device, such as a vacuum tube, transistor, or operational amplifier. Distortion may also be caused by a passive component such as a coaxial cable or optical fiber, or by inhomogeneities, reflections, etc., in the propagation path.

  2. In start-stop teletypewriter signaling, the shifting of the significant instants of the signal pulses from their proper positions relative to the beginning of the start pulse.

    The magnitude of the distortion is expressed in percent of an ideal unit pulse length.

Source: from Federal Standard 1037C in support of MIL-STD-188