Teletypewriter or Modem Signaling
In binary signaling such as FSK, distortion is 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. This is sometimes called 'bias' distortion.
Telegraphic distortion is a similar older problem, distorting the ratio between "mark" and "space" intervals.
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