Engaged" Vs. "Disengaged" Tapes - Alesis AI-2 Reference Manual

1.5 "ENGAGED" VS. "DISENGAGED" TAPES

Analog audio recorders typically move tape past the heads between
1-7/8 and 30 inches per second. Higher play speeds result in a
higher bandwidth, or the ability to record high-frequency signals on
tape.
ADAT digital audio signals require a much higher bandwidth than
analog audio. To provide the increased bandwidth required, the
ADAT uses a VHS mechanism, which has a head drum that rotates
at very high speeds and records the digital audio on diagonal tape
tracks. This has the same effect, as far as the head is concerned,
as moving the tape at a much faster speed.
With ADAT, the tape is "engaged" if the tape is not moving, but is in
contact with the rotating head. This allows the ADAT to go into
Play or Record, instantaneously. When the AI-2 puts the system
into Still or Stop, the head remains spinning and the tape is not
disengaged.
When the tape is "disengaged", the ADAT head stops rotating and
the tape moves away from the head -- to prolong both tape and
head life. If the tape is disengaged, the ADAT will take slightly
longer to go into Play or Record as the tape has to engage. This
type of transport operation is identical to the operation of a normal
video tape transport.
The AI-2 will disengage the ADAT tape if it receives an Allstop
command and will engage the tape on receiving any transport
command, including Stop. The ADAT transport will automatically
disengage the tape to minimize wear if no transport activity occurs
after a period of 4 minutes.
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