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SMPTE Synchronization Overview, Chapter 16
16-6 ALESIS M20 REFERENCE MANUAL 1.06
16.3B INTERNAL GENERATOR ABS OFFSET
This is set in INT GEN EDIT mode, pages 2 and 3 (see section 11.7c).
This is used when you want to issue time code from the M20 based on the ABS time plus an
offset, usually to record on the TC track of the M20 and/or an external recorder. This is
most often used when pre-striping tapes, or when the M20 is a master in a system.
Example: If the ABS offset in INT GEN is set to 12:00:00, and INT GEN and the TC
INPUT switches are on, the M20 will generate SMPTE time code starting at 12:00:00
at ABS time 00:00:00. To see this clearly, set the Tape Counter to ABS and the
Reference Counter to INT GEN.
When you rewind or fast forward the M20 in this mode, it will not issue time code from the
internal generator until you enter Play mode again (at which point the INT GEN display will
immediately “catch up” to the ABS time plus the offset).
16.3C TAPE OFFSET
Tape Offset in the M20, as in all ADATs before it, is designed for offsetting one ADAT from
another, usually for the purposes of digital copying one section of tape to a different location.
In a multi-ADAT system, the Tape Offset allows any ADAT to be ahead of or behind of the
master time location. But the Tape Offset button is not used for setting an offset from
incoming SMPTE Time Code: that is set in the first page of the SMPTE Chase menu.
Tape Offset in SMPTE Chase mode is exclusively for offsetting slave offsets from the ID1
ADAT.
If you press Tape Offset on the top ID1 ADAT, it turns on Tape Offset on all ADAT slaves
and sends them a message setting their Tape Offsets so they will be ahead of or behind the
top ADAT by the specified amount. This overwrites whatever the slaves’ Tape Offsets were
previously.
If the Tape Offset of a slave (ID2 and above) ADAT is turned on, only that particular
machine will be offset. Each slave may have its own tape offset (but, as noted above, if you
turn Tape Offset on the master machine, the slaves’ offset values will be overwritten).
If the top ID1 ADAT is in SMPTE Chase mode, and has a Tape Offset, it will not affect the
relationship between the top ADAT and the incoming time code. (Effective with Version 1.01
software.) Any ADAT slaves below the master will be offset from the master, and from
incoming time code, by the specified amount.
Example: If the top M20 is in SMPTE Chase mode, with ABS as the Chase Reference, a
SMPTE offset of -1 hour, and a Tape Offset of -10 minutes, incoming time code of one
hour will cause the master to chase to 01:00:00 SMPTE time (00:00 ABS time). The
bottom M20s or ADATs will be at 01:10:00 SMPTE time (10:00 ABS time), as long as
their Tape Offset buttons are lit.
If a slave ADAT is offset to a point out of tape range (for example, if the master is at a point that puts
the slave at the LEAD section at the beginning of its tape), the message “Tape Offset Standby” will
appear. When the master advances to a point where the slave is past 00:00:00 ABS time, audio will
start automatically.