Matt Ion,
  In a message on 23 March, you wrote to me in part :
MI> for "bias".  Anyone who knows how the process works will realize the inhe
MI> problems with this :)
A range of magnetic fields from the quantum[?  ] minimum to some higher power
level magnetize metal and oxide (Fe, Cr, et al.  ) "nonlinearly".  This 
ffect
is not frequency dependent, so a supersonic freq magnetic field of adequate
strength puts all audible material in the zone of linear response.  ?  I
hadn't really considered that program material biases the tape, and that 
XPro
fixes this to maintain a more constantly normal bias.  The first magnetic
recordings were on iron wire, and unbiassed, I think I read, the highest bias
frequency I recall from the 80s is 125khz.  
MI> One advantage to using the high-frequency sine wave is that it's naturall
MI> filtered by the limitations of the playback head itself (most of which wo
MI> respond to a signal beyond 17kHz or so).
Heads of kinds of ferrite and of "permalloy"; some, Hall-effect.  Others? 
Certain play heads can read shorter wavelengths than record heads can
write, for equivalent gap size, because ?    
MI> course, an alternating field is also far more efficient at erasing the ta
A stronger, video bulk tape eraser is needed to erase metal audio tapes, or 
was
several years ago.
Recent articles say stronger magnetic fields are being created every several
months. And this work may help recording progress.      
...
 * ATP/qwk 1.42 * "...but the traffic never slows."  -- Sara Hickman  
"Shortsto
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 * KMail 3.10m  1996:  The year of the BBS!
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