Well, I know it's kind of confusing, but the HiFi track indeed IS analog (but "not really", as I said), only that the audio is not electromagnetically printed onto the tape, but intermodulated (up-modulated) with the picture itself. It doesn't matter if the picture is simply black, of course. ADAT technology is real 16 (later 20) bit digital PCM AFAIK. Those SVHS tapes were just readily available at the time, and the tape formula was made for an acceptable error rate. The machines weren't though :)