Appsys ProAudio ADX-32A, User Manual

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User's Manual
For audio distribution to several places, up to 32 ADAT Multicore Extenders can be daisy-chained
together. This feature can be used for complex setups, e.g. multiroom audio distribution or the
connection of additional monitoring equipment. Each ADAT stream can be fed into the Cat5 at
an arbitrary place and is then distributed to all other connected devices.
All ADAT connections work completely independent of each other. This makes it possible to
transmit different data formats, sample rates, resolutions etc. at the same time over the same
Cat5 cable. This allows not only the ADAT protocol extensions S/MUX (DS/Double speed,
24bit/96kHz over 2 optical cables) and S/MUX4 (QS/Quad Speed, 24bit/192kHz over 4 optical
connections) but also many other encodings (S/PDIF, AES/EBU, AC-3) to be transmitted.
5. Theory of operation
5.1. Optical transmission
The commonly used ADAT Lightpipe interface (actually called “ADAT Optical“) uses Plastic
Optical Fiber (“POF“) as transmission media. POFs are very cheap and immune to
electromagnetic interference, but are limited to approx. 16ft (5m) transmission distance. Larger
distances cause problems as the light pulses are attenuated too much, leading to data errors
which usually result in drop-outs or crackles. Furthermore, POFs are also very sensitive to breaks
and sharp bends which may be a problem in harsh stage environments.
5.2. Electrical transmission
Electrical transmission over twisted pair cabling (e.g. Cat5) allows much longer distances than
POFs. Especially Cat5 cables are, as Ethernet cables, commonly used and very economic (many
buildings have Cat5 cables laid out already). Also, bending is not a problem, and for harsh
environments (like stage use), there is a selection of specially designed cable assemblies and
cable reels available, often using ruggedized Neutrik EtherCon® connectors.
Cat5 cable consists of four twisted pairs, each made up of two single wires. One pair can carry
one ADAT stream (8 channels), yielding a total transmission capacity of 32 channels.
The transmission method used on the Cat5 media is called “differential pair signalling” or
“balanced transmission”. This means that each signal is transmitted over a wire pair, where one
wire carries the inverted signal of the other one. In contrast to unbalanced (ground-referenced)
systems, differential signalling provides very good noise immunity, because coupled noise affects
both wires the same way and can be eliminated at the receiver's side by simply taking the
difference out. Additionally, EMI is greatly reduced because the electric and magnetic fields
surrounding the two wires cancel each other out.
The technology used in the ADAT Multicore Extender (RS-485) has been used for a long time,
e.g. for lighting applications (DMX) or harsh industrial environments (Profibus). The commonly
used AES/EBU standard works in a similar manner, but is, due to its relatively low data rate, only
able to transmit two audio channels over one pair. State-of-the-art technology is used in the
ADAT Multicore Extenders to ensure reliable operation at the higher data rates required by the
ADAT protocol.
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