signal that results from a positive air pressure on a transducer will be deemed 'hot'. Pin 2 has been designated as the 'hot' pin, and that designation serves useful for keeping a consistent polarity in the rest of the system. Since these conductors travel the same path from source to destination, the assumption is that any interference is induced upon both conductors equally. The appliance receiving the signals compares the difference between the two signals (often with disregard to electrical ground) allowing the appliance to ignore any induced electrical noise. Any induced noise would be present in equal amounts and in identical polarity on each of the balanced signal conductors, so the two signals’ difference from each other would be unchanged. The successful rejection of induced noise from the desired signal depends in part on the balanced signal conductors receiving the same amount and type of interference. This typically leads to twisted, braided, or co-jacketed cables for use in balanced signal transmission. Balanced and differential Many explanations of balanced lines assume symmetric signals (i.e. signals equal in magnitude but of opposite polarity) but this can lead to confusion of the two concepts—signal symmetry and balanced lines are quite independent of each other. Essential in a balanced line is identical impedances in the two conductors in the driver, line and receiver (impedance balancing). These conditions ensure that external noise affects each leg of the line equally and thus appears as a common mode signal that is rejected by the receiver. There are balanced drive circuits that have excellent common-mode impedance balancing between the legs but do not provide symmetric signals. Symmetric differential signals concern headroom and are not necessary for interference rejection. Baluns Interfacing balanced and unbalanced lines requires a balun. For example, baluns can be used to send line level audio or E-carrier level 1 signals over coaxial cable (which is unbalanced) through of balanced category 5 cable by using a pair of baluns at each end of the CAT5 run. As the signal travels through the balanced line, noise is induced and added to the signal. As the CAT5 line is carefully impedance balanced, the noise induces equal (common-mode) voltages in both conductors. At the receiving end, the balun responds only to the difference in voltage between the two conductors, thus rejecting the noise picked up along the way and leaving the original signal intact. A once common application