Music Production 7 min read Updated: October 2026

Balanced XLR vs Unbalanced TS/RCA: Common-Mode Rejection Ratio (CMRR) Explained

In audio studio cabling, the difference between an unbalanced instrument cable (TS guitar cable or RCA interconnect) and a balanced cable (XLR microphone or 1/4" TRS cable) is the principle of Common-Mode Rejection.

The Balanced Transmission Scheme

A balanced audio cable contains three conductors: Ground (shield), Hot (in-phase signal $+S$), and Cold (polarity-inverted signal $-S$).

As the cable travels past electromagnetic noise sources (lighting dimmers, power transformers, RF antennas), electromagnetic interference ($N$) couples equally onto both the hot and cold wires:

$$V_{\text{hot}} = S + N \qquad V_{\text{cold}} = -S + N$$ $$V_{\text{out}} = V_{\text{hot}} - V_{\text{cold}} = (S + N) - (-S + N) = 2S$$

Common-Mode Rejection: differential amplifier subtracts cold from hot, canceling noise $N$

At the receiving destination, a differential amplifier subtracts the cold signal from the hot signal. The inverted audio signals combine constructively ($2S$), while the induced noise is cancelled out entirely.

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