I know a guy who claims that he can hear when a digital audio signal
cable produces jitter or other data transmission errors like retries
and too many handshake requests.
What can a cable do wrong?
Firstly there may be undefined and changing contact resistance
at the plugs and at the crimp connections.
Then there may be a bad shielding and interference with local EMF
fields from 50/60 Hz up to the whole radio band frequencies.
Although they are analog signals, they add to the digital signal
in form of jitter noise.
Then there are reflections at both cable ends if not within the cable
itself also. The impedance at the connector ends changes a little even
in a good cable. You have to unroll the individual wires and spread
them out for the crimp or solder pins. The way how that is done
influences the standing wave ratio, SWR, of the transmission line.
Reflections also add to the jitter noise and cause parasitic mantle
currents. The cable may start to transmit like an antenna.
Thousands of times the governmental radio monitoring services
had to search and find bad digital data transmission cables,
mostly from badly connected computer networks.
A digital audio connection is just such a thing.
When you have bad luck, and the cable lengths fit into the civil
air band airport tower frequency of your neighbouring airport,
you better hide when they come after you.
Then there is the question of homogenity.
Has the cable been bent sharply, quenched or otherwise
mechanically mistreated?
While the above sales advertizing is rather laughable,
no RF engineer will laugh when it comes to low noise
HF transmission over cables with connectors in between.
The engineer will have a bad time unless everything is thoroughly
checked with oscilloscopes, frequency analyzers, SWR bridges
and reflectometers.
This was the main thing in short, but the list is incomplete.
w.
