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L-8 / Jan 2015
W H E A T N E T - I P 8 8 c b l C O N S O L E B L A D E 3
• for an audio output from the BLADE3, the same connections can be made as
are used for the inputs
• although not recommended, connections can be made with shielded twisted pairs,
such as is normally used for balanced analog audio connection
• for an audio input to the BLADE3, connect the unbalanced source hot wire to
one wire of the twisted pair and the unbalanced source ground to the other wire
of the pair – at the BLADE3 end, connect the wire carrying the hot signal to the
RJ-45 HI pin and the wire carrying the ground to the RJ-45 LO pin – connect
the shield to a convenient ground connection at one end only – typically when
equipment is being connected in this fashion you choose to make your ground
connection consistently at either the source or the destination, using the same
grounding scheme wherever in the system such connections are made
• for an audio output from the BLADE3, the same connections can be made as
are used for the inputs
• adapters are commercially available with RJ-45 connectors on one end and the
appropriate audio connector type, such as RTS or XLR, on the other
• balanced to unbalanced adapters, also called baluns, are commercially available to
transform the unbalanced connection to a balanced connection – these are usually
active devices and will account for level differences as well as converting between
balanced and unbalanced connections
• For digital audio connections always use a good quality digital audio cable with a
characteristic impedance of 110 ohms.
The AES/EBU specification, with its broad impedance tolerance, allows for cables with
impedances from 88 ohms to 132 ohms – 110 ohms is ideal. Twisted pair cable should be shielded,
and in the case of multi-pair cable, each pair should be individually shielded. Foil shielding is
recommended for permanent installations and foil shield plus overall braid should be used in
applications where frequent flexing of the cable will occur. One cable pair is capable of carrying
two channels of digital audio.
Generic “audio” cable such as Belden 8451
may
be used for interconnecting
AES3 digital audio devices but
only
for distances of less than about 25 feet. The
actual cable length that will work satisfactorily in an installation is primarily de-
termined by the error correction and jitter tolerance of the AES3 receiver device
and the cable used.
The impedance of most “analog” cables ranges from 40 ohms to 70 ohms and represents a large
impedance mismatch from the nominal 110 ohms required in the AES3 standard. Such mismatch
will result in signal reflections, causing bit errors at the AES3 receiver. The higher capacitance of
generic analog cables also slows down the rise time of the digital data signals, impairing the ability
of the AES3 receiver to accurately detect digital signal transitions. This may result in increased jitter.
