Re: Ampex Quad scanning
As PaulM says you record 15.625 lines per sweep - but you cannot replay that because you would have a head switch (disaster) in the middle of the active line. So, on replay the actual number of lines read off the tape varies per head as you have to either advance or retard the switch point to occur in the horizontal blanking period. The sequence of integer lines read back per head revolution (starting with head 1) is 15,16,16,15,16,15,16,16 so over 8 head passes you have your average of 15.625 lines.
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