MOTU 8M User Manual page 43

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.
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 47. 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).
H A R D W A R E I N S T A L L A T I O N
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 48.
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 48. 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.
When the 1248 clock mode is set to any other
source besides S/PDIF, then sample rate conversion
is automatically enabled for the input, which can
record any S/PDIF signal up to 96 kHz. This is not
an exact bit-for-bit digital transfer, but
sophisticated filtering is applied to ensure the
highest possible audio quality.
The S/PDIF output is not equipped with sample
rate conversion, so it always outputs at the 1248's
current operational sample rate (item #13 on
page 18).
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