I just don’t get it. The reason behind using XLR connectors is to eliminate noise, hum and whatever other signals coming from alien planets from the audio signal.
"This process is called Common Mode Rejection Ratio or CMRR and it is used to eliminate noise and hum which can be common to a signal. CMRR is most often taken advantage of in XLR balanced cables but it can also be used in single ended RCA cables as well. How does this work? Imagine a two-wire cable going from a turntable to a preamplifier. On one end you have the phono cartridge which is a coil of wire - with a beginning and end wire - each end of the coil is connected to one of the two wires of the cable. The other end on the preamp has a differential stage amplifier and on each of the two inputs we place the other end of the wire. With me? Now we start to play a record. The coil generates a moving voltage which is different at each end of the coil - it’s AC so it’s going + to - and then - to + so the voltage is moving back and forth over the coil - the signal always the opposite on each end of the coil wires. Our differential stage is loving this - it amplifies the differences between each end of the coil as the signal moves back and forth and we hear music. Now imagine a noise source - hum from a nearby transformer, noise from a cell phone or anything radiated in the air. That radiated noise is going to pass right through our two wires and be present on each of the two wires in equal amounts. So each of our two wires has lots of noise on it but the noise on each of the two wires is identical. The noise is common to the two wires. What does our difference amplifier do with this? Nothing! It rejects the noise completely. So you have high noise and signal coming into the differential stage and only signal coming out with the noise gone! It’s a bloody miracle. And there, my good readers, you now understand Common Mode Rejection, how it is rejected while at the same time amplifying only the music. XLR cables do this best because they have the two wires inside them surrounded by a third wire that is called a shield. An RCA cable has only one wire and the shield and they are not equal in construction so the noise isn’t as common as it could be and thus rejected not quite as much."
Can somebody here explain to me why $3,000 XLR connectors supposedly have a better CMRR than say $100 XLR connectors? Thanks in advance.