Quite correct - "common mode rejection".fizzcat wrote: If I understand this correctly the pins 2 and 3 float relative to ground and act like a twisted pair in telephone lines. Pin 1 is connected to ground and a shielding mesh or sleeve around the outside of the signal pair. The actual signal is taken from the difference between the floating cables, so that the EMI can be filtered out - it will be picked up equally by the two floating lines and so is ignored by the differential amplifier.
To connect a 3-pin output (Shure SM58) to a MONO input, pins 1 needs to be linked to pin 3. This looses the benefit of common mode rejection, but it means that pin 3 is tied to ground and not floating, so you will get the proper signal voltage across 2 and 3.
http://www.mediacollege.com/audio/conne ... -mono.html
