@avavsystems I used to have a Voice of Music reel-to-reel (model 720 or 722) with “Add+A+Track” which was the inverse of Sel-Sync: it would play back the overdubbed track from the record head, i.e. the tracks are not in sync on the tape. Recently learned about “Staggered Stereo” which it could also play (and record?). Machine vanished at some point but online descriptions allowed me to figure out the offset (.16666... ms--1.25” at 7.5ips) and restore a master recorded that way back in 1982.