Apparatus for processing an input data signal includes a generator (64) providing a plurality of pseudo-random signals each of which scrambles the input data signal in one of a plurality of mod. 2-adders (62a to 62d) to provide a plurality of respective scrambled outputs, a detector (65) in which a DC component, such as a run-length or a digital sum value, is detected for each of the scrambled outputs, and a selector (67) responsive to the detector (65) for selecting the one of the scrambled outputs, for example having a minimum run-length or a digital sum value closest to zero. An identifying signal identifying the pseudo-random signal used in scrambling the selected scrambled output is then transmitted with the latter, for example, by recording on a magnetic tape. When the transmitted signal is received or reproduced, the identifying signal included therein is detected, and the received signal is descrambled with a pseudo-random signal corresponding to the detected identifying signal.
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