emrath (01/05/83)
#R:rocheste:-36000:uiucdcs:22700006:000:1176 uiucdcs!emrath Jan 4 15:57:00 1983 I think tape head demagnetization is a throwback to days when things like DC bias were used and demag was necessary. I have tried making careful measurements in my lab of the effects of demagnetizing heads and so far have yet to be able to measure any (much less hear them). Note that I have successfully measured noise outputs down to about 5 microvolts (100dB S/N re .5V, the eia std). I am fairly confident that I am not washing out tape deck differences (before/after demag) with my measurement techniques, unless those differences are less than 1 or 2dB, which are insignificant. The difference between various brands of tape can be greater than this. I bought one of those TDK jobs and it had a nice booklet explaining what specs MIGHT be affected by using it, but I sure couldn't measure any change. My belief is that the deck simply doesn't (and never will) need demagnetizing. I have read every recent article in the trade rags about head demagnetizing and they all seem to conclude that nobody really knows for sure whether head demag is necessary, but it doesn't hurt. I say, if it doesn't help, why bother. Besides, it is a procedure that is fairly easy to botch.
whaley (01/09/83)
#R:rocheste:-36000:uiucdcs:22700008:000:328 uiucdcs!whaley Jan 9 12:23:00 1983 Not only that... If the head has no mag field it won't erase more due to the difference between it and the bias. In voltage, everything is relative. One speaks of differences. If there is no magnetic field, the not there magnetic field won't erase anything. Differences are not applicable to fields, at least not this way.