Digital Audio In/Out; About 16-Bit And 20-Bit Signal Transfers - Alesis ADAT-XT20 Reference Manual

D
IGITAL
The digital input and output carries all eight tracks on a single fiber optical
cable. This allows you to bounce audio between multiple machines within the
digital domain. The ADAT Optical cables carry digital audio between
multiple XT20s and ADATs, and to ADAT Compatible™ products such as the
QuadraVerb 2, Q20, many Alesis keyboards, the ADAT-PCR computer interface
card, and third-party products such as the Digidesign ADAT Interface and
Yamaha 02R digital mixer. Since the fiber optic connector carries the digital
information for all 8 tracks, it is also useful for backing up all tracks in one pass
(see Chapter 6 for more on digital audio).
Digital bussing requires a fiber optical cable (included) for each XT20 in the
system (or any other ADAT-compatible product). Additional cables are
available from your dealer in various lengths up to 16 feet. This connection can
be made while power is on or off, and the machines do not need to be turned on in
any particular order. Note: To bounce tracks within a single XT20, it is not
necessary to connect the optical network.
A
BOUT
ADAT XT20 Reference Manual
A I /O
UDIO N
16-
BIT AND
All data on the ADAT Optical cable is in a 24-bit word length; in 16-bit
mode the eight least significant bits are filled with zeroes, in 20-bit
mode the last four bits are zeroes. If 20-bit data is sent to a 16-bit
machine, the four "extra" bits are simply ignored. Only ADAT Type II
machines (such as the M20, XT20, LX20, and PCR card with proper
software) can receive a full 20-bit transfer via the optical cables (and
then only if the tapes in those machines was formatted in 20-bit mode).
If you need to transfer audio from a Type II tape to a Type I tape you
have three options:
Transmit at 20 bit, and the receiving unit will ignore the last
four bits, essentially cutting them off.
Press the [DIGITAL OUT] button (located on the right above
the RECORD button) until the display reads:
Ovt 16
ABS
This cuts off the data in bits 17-20 and fills the "extra" 4 bits
with zeroes at the transmitting end. In most cases, this has the same
sonic results as Method #1.
Press the [DIGITAL OUT] button (located on the right above
the RECORD button) until the display reads:
Ovt 16dt
ABS
This adds dither, a specially shaped mathmatical noise, to
the conversion process which "smoothes out" the transition at low
levels and allows you to get better resolution even though the result is
still 16-bit. However, if the signal will be dithered again later, you
may want to use one of the first two methods.
UT
20-
BIT SIGNAL TRANSFERS
Connections: Chapter 3
39