Lab.gruppen PLM 20000Q - Manual (Page 100)

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Application Guide
PLM Series Operation Manual rev 1.2.3
The distance allowed between a signal source and the PLM is dependent on both cable quality and the
sampling rate used. At a 96 kHz sampling rate, any good quality AES3 cable should allow a cable run of
100 meters with no data losses beyond the capability of internal error correction. The best cables may allow
longer cable runs, though careful trials are recommended before use in the field. Sampling rate also governs
allowed cable length; a 100 meter length at 96 kHz might extend to 200 meters at 48 kHz, but be cut to
50 meters at 192 kHz.
10.6.3.4 Signal Degradation and Loss
A weak or degraded AES3 signal will exhibit no audible loss of quality as long as the robustness of the
data stream remains above the threshold required for internal error correction. As degradation approaches
the threshold, audible artifacts may be heard, including pops, clicks and momentary dropouts. Any such
indications require immediate attention, as often the window of acceptable data loss between artifacts and
complete audio loss can be very narrow.
As a precautionary measure four touring applications, it is advisable to configure all digital audio wiring
prior to use. It is recommended that all cables be tested for error-free performance at lengths 20% to 25%
greater than lengths to be used in the field in order to provide a comfortable margin of safety.
10.6.4 External Signal Distribution Hardware
10.6.4.1 Distribution Amplifiers
Dedicated distribution amplifiers for AES3 signals are available from several manufacturers. The most com-
mon format is one input and six outputs. Digital distribution amplifiers are designed to refresh or reconstruct
the signal as well making up for line losses.
One type of distribution amplifier is a simple repeater, which restores the waveform shape and brings the
signal amplitude back up the required level. Some distribution amplifiers also offer a re-clocking feature,
which also re-times the signal to prevent signal degradation from clocking errors known as jitter.
Distribution amplifiers that offer re-clocking often make the feature optional as using re-clocking can intro-
duce small additional amounts of latency, so should not be used unless necessary.
10.6.4.2 Passive splitters
In some limited applications, a single AES3 input may be split into two signals using a simple passive
splitter. Splitters provide a convenient and low cost solution when only one additional signal is required, and
in situations where cable lengths are short. Attenuation is minimal, but there is no refreshing of the signal.
10.6.5 Additional Reference Material
Complete technical information on the AES/EBU (AES3) standard can be downloaded from the AES web
site at http://www.aes.org/publications/standards/.