User Manual

HARDWARE INSTALLATION
46
TRS quarter-inch 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.
Quarter-inch analog inputs are equipped with
high-quality, digitally controlled analog trim that
provides a 22dB range (+2dBu to +24dBu) in 1dB
steps.
Outputs can be trimmed at the digital stage, before
the DAC. Range is 16 dB.
Trim controls are most easily accessed in the web
app. See “Device tab” on page 18. Trim settings can
also be accessed in the LCD menu.
Optical
Your MOTU audio interface provides two banks of
ADAT optical (“lightpipe”) connectors. Each bank
provides an input and output connector. Together,
they provide 16 channels of ADAT optical digital
I/O at 44.1 or 48 kHz, or 8 channels at 88.2 or 96
kHz. The optical ports are disabled when the
interface is operating at a 176.4 or 192 kHz. At the
high sample rates (88.2 or 96 kHz), 4-channel
SMUX operation supports two modes (item #26
on page 19):
■ 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 #26 on page 19). 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) your MOTU interface, as explained in
“Synchronization” on page 51. There are two ways
to do this:
A. Resolve the optical device to your MOTU
interface
B. Resolve your MOTU interface to the optical
device
For A, choose Internal (or anything other than
ADAT A or B) as the clock source in the Device tab
(page 18).
For B, choose either ADAT A or ADAT B as the
clock source (page 18). Be sure to choose the
optical port that the device is connected to.
Using word clock to resolve optical devices
If the optical device has word clock connectors on
it, you can use them to synchronize the device with
your MOTU interface. See “Syncing word clock
devices” on page 52.
S/PDIF with sample rate conversion
The 1248 provides S/PDIF digital audio input and
output. Be sure to review the digital audio clocking
issues, as explained in “Syncing S/PDIF devices”
on page 52. The S/PDIF input is also equipped with
sample rate conversion, which allows you to
capture digital input without digital audio sync.
You can even record S/PDIF input that is running
at a completely different sample rate than the 1248’s
current sample rate.
When the 1248 clock mode (item #13 on page 18)
is set to S/PDIF, the 1248 resolves to the incoming
S/PDIF signal and no sample rate conversion
occurs. In this scenario, an exact bit-for-bit digital
audio transfer is accomplished.