Term: CMRR

Common Mode Rejection Ratio: This ratio gives an indication of the capacity of a device for rejecting common mode signals, ie signals which are applied simultaneously to the pair of conductors of a balanced cable (noise). When the common mode signal arrives along with the audio signal at the input of balanced audio, it eliminates the common mode signal (with same polarity) and amplifies the audio signal with reversed polarity. With unbalanced devices, the CMRR can be very low (about 10 dB) and balanced devices can be about 30 dB. If we need a significant increase of CMRR, we need an audio isolator which works through transformer. If the transformer is a quality transformer we can improve our noise rejection getting a CMRR of 120 dB.