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i'm hoping someone will help me out to understand the difference (if there is a difference) when using an older SD mixpre which has outputs that are impedance balanced, vs. an newer mixpre that has active balanced outputs when using it as a front end to feed signal into ch 3/4 of a 744T. i've got a few other questions: are there differences in quality, level, rf/interference rejection or other? is active-balanced and balanced the same thing? when going through an xlr how does impedance balanced avoid interference by having only one voltage line when compared to balanced that has 2 lines? i've read the paper on the differences (http://www.sounddevices.com/tech/balancing.htm). so for impedance balanced outputs, if "This topology has equal impedances from pin 2 to ground and from pin 3 to ground; however, only pin 2 is driven with signal voltage", can someone explain how driving only pin 2 is different from an unbalanced line where pin 2 is also driven with voltage. they say "It provides common-mode rejection of unwanted noise into a balanced output just like an "active" balanced or a transformer balanced output stage." i guess maybe i don't understand what "common-mode rejection" means. sorry if this seems rudimentary to some, i just would like to understand it better. cheers, P.