Adat Optical Digital Inputs And Outputs; About 16-Bit And 20-Bit Signal Transfers; High Sample Rate Operation - Alesis ADAT-HD24 Reference Manual

ADAT Optical Digital Inputs and
Outputs
Each of the digital inputs and outputs of the ADAT
HD24 carries eight tracks or channels (up to 48 kHz)
on a single fiber optic cable in the industry-standard
ADAT Optical format. To cover the 24 tracks of the
HD24, there are three sets of inputs and three sets of
outputs. Connect these outputs if you want to:
copy audio between ADATs within the
•
digital domain
• connect to a digital mixing console
transfer audio to and from a computer
•
workstation with ADAT Optical ports
• receive digital signals from many Alesis
keyboards and effect devices
Digital copying requires three fiber optic cables for
each HD24 in the system (or any other ADAT-
compatible product). Additional cables are available
from your dealer in various lengths up to 16 feet.
When connecting a digital mixer, you'll need six
cables per HD24 in the system.
connections can be made while power is on or off.
Note: To bounce tracks within a single HD24, it is
not necessary to connect the optical network.
About 16-bit and 20-bit signal
transfers
All data on the ADAT Optical cable has always
been in a 24-bit word length; in earlier 16-bit
ADATs the eight least significant bits are filled with
zeroes, in 20-bit ADATs the last four bits are zeroes.
If 24-bit data is sent to a 20-bit machine, the four
"extra" bits are simply ignored, much as fractions of
a penny don't matter when you actually pay your
bill at the gas station. ADAT Type II machines
(such as the M20, XT20, and LX20) can receive a full
20-bit transfer via the optical cables (if the tapes in
those machines were formatted in 20-bit mode).
The ADAT/EDIT system can receive a full 24-bit
transfer, as can many other computer workstations.
If you have a digital mixer, you may need to
upgrade its software or hardware to receive or
generate true 24-bit signals via the ADAT
Optical interface.
ADAT HD24 Reference Manual
1.
2.

High sample rate operation

At the 88.2 and 96 kHz sample rates, the ADAT
Optical format becomes essentially a 4-channel
interface.
Operation".
Digital audio
To transfer audio from the HD24 to
non-24-bit systems you have two
options:
Transmit at 24 bit, and the receiving unit will
ignore the bits it can't read, essentially cutting
them off. This option provides the lowest noise
when tracks are going to be processed and
mixed.
Connect the machines via analog inputs and
outputs. This will effectively dither the 24-bit
signal of the HD24 to whatever the receiver is
using. While a digital transfer is theoretically
best, today's converters are of such high quality
that the difference is usually not audible.
See Chapter 7, "High Resolution
chapter 2 • connections
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