Actually, balanced circuits have nothing to do with signal symmetry. Rather, it refers to the balancing of the common mode impedances. In a balanced circuit, the signal is not bound to be symmetrical around an arbitrary point (like ground) but will be divided according to the mismatch of resultant generator / load impedances. Further, there is no obligation to have a higher output level, though this might result with some topologies. This subject is rather basic, yet in the audiophile community there seems to be a great deal of misunderstanding. Consider a phono cartridge. This is a nearly perfect balanced generator, yet defies the definition of a "three wire circuit". None-the-less, you would be hard pressed to define a better balanced generator (nearly perfectly balanced common mode impedance). In a more "typical" configuration where a source is driving a load the advantage of a balanced circuit is in its ability to reject common mode signals. The amount of rejection is defined as CMRR (common mode rejection ratio) and it is typically expressed in dB below the differential level. Here, the impedance balance of the generator and load will affect the CMRR. While it is true that an XLR connector is the standard for use in balanced audio circuits, it should be noted that it is not the connector that makes a device balanced and that balanced is not an absolute term. One product can be much more balanced than another. Kevin Halverson
