MI> In essence, boosts the high end going to tape, and reduces
  > it (and hiss along with it) on playback.  It's a little
This is the definition I got from my tape manual:
Dolby NR system:
        A system that eliminates tape hiss noise by boosting
low-level signals in the high-frequency range during recording, then
lowering them during playback.
Does hiss consist of high-frequency noises?  By this definition
if the hiss contains any low-frequency sounds, it won't be
eliminated.
MI> HX stands for Headroom Extension.  It operates only during recording; the
  > record bias is adjusted automatically depending on the
  > signal content.  If there's a lot of high-frequency energy
  > in the signal, the bias is reduced to avoid saturating the
  > tape, to improve headroom.'
And what does headroom do?  Why is saturating the tape bad?
What is the purpose of the bias in the tape?
Sorry if I sound dense, but I don't know how analog signal works.
I have no idea how music is stored on tape.
  > can affect NR's effectiveness.  This alone is an extensive
  > subject that wouldn't mean much without a much more
  > extensive explanation of exactly how the different types of
  > NR work.
Can I get a book on this ?  :)
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