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There have been four versions of the ATRAC data reduction system, each claimed ( by Sony ) to more accurately reflect the original audio.

Early version players are guaranteed to play later version ATRAC audio because, as stated, there is no processing required for replay.

Version 1 could only be copied on consumer equipment three or four times before artifacts became objectionable ( the ATRAC on the recording machine attempts to data reduce the already reduced signal ).

By version 4, the potential number of generations of copy had increased to around fifteen to twenty depending on audio content.