And so it came to pass, on 03-21-97 22:32,
   that Kenneth Parrish spake unto Matt Ion:
MI>> sine signal, typically 40kHz-80kHz or higher, that boosts the
MI>> signal on t tape to avoid "zero-crossing" distortion.  
 KP> Weren't tapes originally "biased" with a magnet, some way or other?
 KP>  I don't think it worked quite well. ...  
Well, I can't say from experience (I'm only 28 ;) but we did cover all this 
stuff in an audio-engineering course I took about 9 years ago.  Now that you 
mention it, I do recall hearing that a permanent magnet was originally used 
for "bias".  Anyone who knows how the process works will realize the inherant 
problems with this :)
One advantage to using the high-frequency sine wave is that it's naturally 
filtered by the limitations of the playback head itself (most of which won't 
respond to a signal beyond 17kHz or so).
PMs were (and probably still are, in some instances) also used for the "erase 
head".  This, of course, has obvious drawbacks of its own as well... such as 
the stray magnetic field that would always be present in the general area.  
Of course, an alternating field is also far more efficient at erasing the 
tape.
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Love, luck, and lollipops...
Matt


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