Two Locked ADATs – Different Head Hours?

How is it possible that a pair of (or more) ADAT’s that have always been locked together as one system would have different amounts of head hours on them? In theory they should never get off by much. Obviously they will be off by a little bit just due to the various contortions they go through locating and synching to one another, but we have learned from rotating machines in and out of our studios that they do get off by quite a lot sometimes. The folks at Alesis theorize that this has to do with the two different stop modes of ADAT’s. When you first press stop on an ADAT the tape stays in contact with the head and the head continues to spin, thus accruing head hours. If you press stop a second time the tape is removed from the head and the head is stopped – no head hours accumulate. Differences in when the two stop modes are used from machine to machine can certainly cause one to rack up more head hours than another. Also, after a few minutes of sitting in the first stop mode the machines will time out (see WFTD time out above), automatically stopping the head and pulling away the tape. Differences in the length of time it takes machines to time out in this way can also lead to variances in head hours. The bottom line: This is nothing to worry about. Go make music.