"Jim H" wrote in message


By my understanding pros use quite ordinary quality XLR cable,
because by design it is almost immune to noise.

It's not the cable, its the equipment at both ends that makes the
difference.

There are three main differences between consumer and true audio production
grade equipment vis-a-vis inputs and outputs:

(1) Balanced I/O. Audio production equipment sends the signal down two wires
in the audio cable, with opposite polarity. Consumer equipment sends only
one signal. The benefit comes at the receiving end where the signals are
subtracted, canceling out any noise that is picked up by both wires and
doubling the desired signal.

(2) Higher signal levels. CD players generate some of the highest working
voltages of any piece of consumer audio equipment, which generally peak out
at about 2 volts. Audio production equipment generally works with signals
that peak out at 6.8 volts or more, often quite a bit more.

(3) Lower impedances. Consumer audio gear generally involves input
impedances of 100K, 50K, 2K, but rarely lower. Audio production equipment
has input impedances of no more than 20K, often 10K frequently 6.8 K or 2K
and sometimes as low as 600 ohms. Low impedance inputs are less susceptible
to interference and generate less thermal noise.

I wonder why XLR hasn't filtered down to the mass market?

Mass market systems are simple and relatively non-critical. Audio production
equipment is often used in complex setups which are more prone to have
grounding problems and pickup other kinds of noise.

It couldn't be because they do quite well selling us overdesigned phono
cable!

That would be the high end...

To be fair, there is some high end equipment that uses balanced I/O and
standard audio production signal levels and impedances.