Mic pre



Can anyone shed light on what CMRR refers to in reference to mic pre specs, as in ".....has excellent CMRR....."
I notice there is a professional body called the Center for Magnetic Recording Research. Could not find any reference to a specification that would make sense when applied to a mic pre.
Any help would be appreciated.
Peace and thanks,


Common Mode Rejection Ratio has to do with "balanced" inputs. Some mic pre's use transformers (true balanced) and some use differential input circuits. Basically it's to reduce noise, hum, etc. Don't know how technical you are so forgive me if I'm using a simplistic example. The transformer has a center tap in the winding that is connected to ground so that a nasty hum that shows up at the top and bottom of the winding (the input) will cancel to ground via the cener tap. Therefore a good CMMR means the preamp will work well in electrically noisy conditions. If you're familiar with electric guitars it's like the difference between a Strat -- poor CMMR and a Gibson with hum bucking pickups -- good CMMR

-- Geoff W