definition of balanced mode vs. single ended

I suppose it's possible to carry two balanced channels on a single 5-pin connector, but in audio one usually finds an XLR connector with three pins (hot, cold, ground) plus the barrel. The barrel can be connected to a shield or directly to the ground pin, but typically the barrel is left floating. BTW, I would doubt that a balanced cable makes much difference (even on long runs) when attached to a component that isn't full-balanced. Such components often add a phase-inverter to derive a balanced output. The additional electronics at the balanced output may degrade the sound relative to the RCA outputs. An external XLR/RCA converter plug uses just the hot/ground pins of the XLR junction to derive a single-ended signal for the RCA, discarding the inverted signal on the cold/ground pin side. In this scenario, half the circuitry in your expensive full-balanced component goes to waste.

There is convenience for both applications as well. Most all home audio that uses balanced connections will sound better than when using single-ended, because that is how the equipment was designed.

Pro audio is benefitted greatly by balanced cables because of length of run, and because of the fact that you can connect multiple lines together to get the lenght you need, simply because of the connector style.

All balanced connections I've ever seen have three pins.

S7horton & Bob Reynolds,

There are some quiddities with pseudo-balanced designs that compromise rather than take the "full-balanced" approach. For example, like Bob I also use transformers in my CDP (Sony SCD-1) to create a balanced signal. The stock SCD-1 is a strange beast-- particularly for a statement product-- insofar as it has fully differentially balanced DAC, but converts to single-ended in the analog gain stage, and back again to balanced using an op-amp based module at the XLR output. This is doubtless a compromise to cut costs in the analog stage, while adding additional electronics that degrade sonics. A passive step-up transformer replacing the entire output stage is a big sonic improvement. The output of the secondaries can be considered balanced insofar as the (-) signal is lifted from ground. But I'm not sure I'd called what the transformer does "true-balanced", in that it does not invert signal so as to provide CMMR.