What are "true" balanced connectors

Each signal is actually referrenced to ground, but the differential receiver only uses the two signal bearing wires to convert the differential signal back to single ended for further handling. 

Balanced inputs are not defined by whether two channels of a stereo amplifier are bridged or not. The concept of balanced inputs is that the input is a differential receiver, where the signals on each wire are equal and opposite polarity. Thr differential receiver subtracts these two signals to reproduce the original signal. The benefit over single ended signalling is noise rejection. If the cable is exposed to a source of electrical noise, that noise will be induced with the same polarity and amplitude on both signal bearing conductors, and since the differential receiver subtracts the signal on both conductors, it cancels out the noise, which is common on both sides of the differential pair. This is how the term “common mode noise rejection” was coined. 

@erik_squires 

 Each signal is actually referrenced to ground,

Not universally true.

 
I should have said referenced to -signal- ground. That is the balance point that both signals share in common. 

@erik_squires 

Balanced signals used to be transmitted by transformer outputs and inputs which were galvanically isolated. 

Best,
E

Galvanic isolation isn’t a requirement for a balanced circuit. The transformer output, unless it is center tapped, is only differential, which is where the value is anyways as far as common mode noise rejection is concerned.