Metric Halo 3d Upgrade Board Set, Руководство пользователя

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ULN-2 Users Guide
154
Copper-Based Digital Audio
The ULN-2 supports 4 channels of digital audio over copper-based connections using the S/PDIF intercon-
nects with the RCA connectors and the AES interconnects using the XLR connectors. Even though only
one of the AES or S/PDIF inputs can be a clock master source at any given time, you can have different
digital sources connected to each of the input connectors at the same time – you use the MIOConsole3d
application to select the active input. Audio routed to the digital outputs will be mirrored by both S/PDIF
and AES outputs. This allows you to send the same stereo pair to two devices at once.
We recommend that you use the AES interconnect mechanism to establish the digital communication be-
tween the ULN-2 and other digital devices. The jitter and electrical noise tolerance on AES interconnects
is substantially better than with S/PDIF interconnects. The AES interconnect standard is equivalent to bal-
anced audio interconnections. If you need to use S/PDIF interconnects, try to use the shortest cables you
can and, if possible, use special purpose 75 ohm S/PDIF or video cables.
The RCA connectors used for S/PDIF are friction fit coaxial connectors. When you connect them, ensure
that they are fully inserted and tight.
The XLR connectors used for AES are fully locking. When connecting to them, make sure that you align the
pins and insert firmly. When you remove the connector, make sure that you release the lock by pressing
the lock release button before you pull the connector out of the ULN-2.
Wild digital input streams are still wild
Normally, when working with digital audio transport, you must take care to ensure that all de-
vices communicating with one another are synchronized to the same audio clock. While you
may find that the 3d digital audio inputs can often recover clean-sounding audio from unlocked
audio devices running at the same sample rate, this is honestly just an accidental quirk of the
over-built quality of the 3d hardware and not a supported scenario .
In production or critical listening situations, please always follow digital audio clocking best
practices and ensure that your outboard devices are properly clock-slaved to the Metric Halo
box, or the domain is properly slaved and locked to your outboard gear.
That said, if you find this quirk useful for a quick audition or casual listening, you are in good
company.
Optical-Based Digital Audio
ULN-2 provides two TOSLINK™ connectors on the back panel. One is a transmit connector and the other
is a receive connector. These connectors are used with Plastic Optical Fiber (TOSLINK) cables to commu-
nicate with other devices. The TOSLINK connectors can be used to communicate with either the ADAT®
Optical communication protocol or the Optical S/PDIF communication protocol. Each port can be inde-
pendently switched between the two protocols via the 3d Console.
The S/PDIF Optical communication protocol allows a device to transmit 2 channels of 24 bit audio at 44.1k
through 192k, along with digital audio clock information.
The ADAT Optical standard allows a device to transmit 8 channels of 24-bit audio at up to 50kHz along
with digital audio clock information.
After the original 8 channel ADAT specification was finalized, Alesis and other third parties extended the
standard to support 4 channels of 24-bit audio at 2x sample rates and 2 channels at 4x sample rates. This
extension of the standard is commonly referred to as SMUX. The ULN-2 automatically supports SMUX
transport over the ADAT Optical connections when the box is in 2x mode (either 88.2k or 96k sampling
frequency) or 4x mode (176.4k or 192k). While operating in SMUX mode, the audio data for each of the
first four “ADAT” channels is placed on pairs of optical channels. ADAT 1 is placed on optical channels