MOTU 1248 User Manual page 53

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 21). 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 58. 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.
H A R D W A R E I N S T A L L A T I O N
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 60.
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 59. 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 #14 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 #14 on
page 18).
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