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HARDWARE INSTALLATION
44
AUDIO CONNECTIONS
Here are a few things to keep in mind as you are
making audio connections to your 8A interface.
TRS quarter-inch analog inputs and outputs
Quarter-inch analog inputs and outputs are
balanced (TRS) connectors that can also accept an
unbalanced plug.
☛ Quarter-inch analog outputs are not
cross-coupled. Therefore, when connecting them
to an unbalanced input, use a TRS plug with the
ring disconnected. Not floating the negative
terminal will short it to the sleeve ground and
cause distortion.
Analog trims
All quarter-inch analog inputs and outputs can be
trimmed. This allows them to support a variety of
standards, including EBU-R68, SMPTE RP-155,
+4dBu, -10dBV, 2vRMS, 1vRMS.
The 8A’s quarter-inch analog inputs are equipped
with high-quality, digitally controlled analog trim
that provides a range from -96 to +22 dB in 1dB
steps.
Quarter-inch outputs can be trimmed in the DAC
itself. Range is 24 dB. The headphone output
provides full trim range from 0 dB to -∞ (-127).
Trim controls are most easily accessed in the web
app. See “Device tab” on page 12. Trim settings can
also be accessed in the LCD menu.
Optical I/O
The 8A provides ADAT optical (“lightpipe”)
connectors (one input and one output). Together,
they provide 8 channels of ADAT optical digital I/O
at 44.1 or 48 kHz, or 4 channels of SMUX optical at
2x sample rates (88.2 or 96 kHz). SMUX operation
supports two modes (item #23 on page 13):
■ Standard — for 2x optical connection to
3rd-party SMUX-compatible hardware products.
■ Type II (Legacy) — for 2x optical connection to
legacy MOTU products that are equipped with
optical ports and support 2x operation.
The optical ports are disabled when the interface is
operating at a 176.4 or 192 kHz.
TOSLink (optical S/PDIF)
Alternately, the optical ports can be configured for
stereo TOSLink (optical S/PDIF) in the web app
(item #23 on page 13). The optical IN and OUT
banks can be configured independently.
Choosing a clock source for optical connections
When connecting an optical device, make sure that
its digital audio clock is phase-locked (in sync
with) the 8A. There are two ways to do this:
A. Resolve the optical device to the 8A
B. Resolve the 8A to the optical device
For A, choose Internal (or anything other than
Optical) as the clock source in the Device tab (item
#13 on page 12). Then configure the other device
to resolve to its optical input.
For B, choose Optical as the clock source (item #13
on page 12), and configure the other device to
resolve to its own internal clock.
SYNCING TO SMPTE TIME CODE (LTC)
The Clock Mode menu (item #13 on page 12)
provides the ability to resolve to SMPTE time code
(Longitudinal Time Code, referred to as LT C ) from
any specified analog or digital input.
When you choose the LTC clock mode setting, the
audio phase lock engine in your MOTU interface
resolves to the incoming time code. (See below for
how to specify the time code input.) This ensures
that audio passing through the interface remains
resolved to time code and won’t drift over time, as
long as the audio is coming from other sources that
are also resolved to the same time code. This also
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