And so it came to pass, on 03-25-97 16:46,
   that Kenneth Parrish spake unto Matt Ion:
MI>> for "bias".  Anyone who knows how the process works will realize
MI>> the inhe problems with this :)
 KP> A range of magnetic fields from the quantum[?  ] minimum to some
 KP> higher power level magnetize metal and oxide (Fe, Cr, et al.  )
 KP> "nonlinearly".  This effect is not frequency dependent, so a
 KP> supersonic freq magnetic field of adequate strength puts all
 KP> audible material in the zone of linear response.  ?  
Absolutely kee-rect :)
 KP> I hadn't really considered that program material biases the tape,
 KP> and that HXPro fixes this to maintain a more constantly normal
 KP> bias.  
Well, any frequency can, depending on how you look at it, act as a bias 
signal for frequencies below it... and once high-frequency signals get above 
a certain point, a separate bias signal becomes less of an issue because of 
the lesser time the waveform spends in that zero-crossing non-linear region, 
and the relatively low level of the non-linearity.  Thus, tape headroom can 
be gained by reducing the level of the standard bias signal somewhat.
MI>> One advantage to using the high-frequency sine wave is that it's
MI>> naturall filtered by the limitations of the playback head itself
MI>> (most of which wo respond to a signal beyond 17kHz or so).
 KP> Heads of kinds of ferrite and of "permalloy"; some, Hall-effect. 
 KP> Others? 
Hmm, can't say as I've ever seen a tape deck that used Hall effect devices 
for playback... interesting concept!
The maximum reproduceable frequency of any magnetic pickup is directly 
proportional to the width of the headgap; any signal whose wavelength for one 
cycle is less than the width of the gap, will effectually not be reproduced.
 KP> Certain play heads can read shorter wavelengths than record heads
 KP> can write, for equivalent gap size, because ?    
See above.  Most decks that use a single record/play head are a trade-off: 
the narrow the gap in the playback head, the higher the frequency that can be 
reproduced.  However, the wider the gap in the record head (to a certain 
practical point, of course), the stronger the signal that can be applied to 
the tape.  This is why "professional" decks have separate record and playback 
heads.
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Love, luck, and lollipops...
Matt


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