This article is from the rec.audio.* FAQ, by with numerous contributions by Bob Neidorff others.
There are professional devices used by engineers to manipulate
the digital bitstream, but they cost several hundred dollars and
are not cost effective for consumers. If you need to make
perfect digital copies of digital copies, buy a professional
digital recorder. Pro models do not have SCMS, are more durable
than consumer recorders, and may have better quality electronics
than consumer models.