https://benchmarkmedia.com/blogs/application_notes/balanced-vs-unbalanced-analog-interfaces?_pos=1&_sid=87340c17d&_ss=r
A lot of informative info before this summary in the link above.
SUMMARYProfessional-grade balanced analog audio interfaces can provide a 12 to 16 dB SNR advantage over unbalanced interfaces due to the high +24 dBu signal levels used on balanced interfaces. Consumer-grade balanced interfaces can only provide 3 to 6 dB SNR advantage due to the relatively low +14 dBu (4 Vrms) signal levels.
In addition, the differential amplifier or transformer in a balanced input can provide an incredible 50 to 100 dB rejection of ground-loop interference. This is usually sufficient to reduce ground-loop interference to completely inaudible levels.
In an unbalanced interface, the shared use of the shield places ground-loop currents in the audio path. Unbalanced interfaces are very sensitive to ground currents flowing between audio components. This is not a problem with balanced interfaces due to the use of dedicated audio conductors.
Copper braid and foil layers provide shielding against RF interference. In a balanced cable, the shield does not carry the audio signal. The audio conductors are fully surrounded by the shield but are electrically isolated from the shield. In an unbalanced system, the RF shield also serves as the audio ground. This dual use of the RF shield, in an unbalanced system, causes a slight increase in susceptibility to RF interference.
Copper braid and foil shields do not provide any protection against magnetic interference. Magnetic fields easily pass through copper and foil. If star-quad cables are used in a balanced system, magnetic interference can be rejected by the CMRR of the balanced input receiver. In a balanced system, 4-conductor star-quad cables can reduce magnetic interference by 20 to 50 dB when compared to standard two-conductor balanced cables.
These numbers should be hard to ignore, but the hi-fi industry has been slow to change. Many high-end audio products still are not equipped with balanced interfaces. Others have consumer-grade 4 Vrms balanced interfaces. These are a partial step in the right direction.
The facts show that it is virtually impossible to achieve state-of-the-art audio performance using unbalanced interfaces. We see this in the lab when we measure balanced and unbalanced interfaces under ideal well-controlled conditions. Outside, in the real world, the advantages of balanced interfaces are larger than a set of balanced vs. unbalanced specifications would indicate on a product data sheet. The differences can be extremely large when ground loops, RF interference, and magnetic interference are encountered in a typical audio system.
Our recommendation? Avoid unbalanced (RCA) analog interfaces whenever possible! Look for professional-grade balanced interfaces when buying audio products. Look for CMRR specifications on balanced inputs. Consider replacing audio devices that do not support balanced interconnects. These unbalanced-only devices are probably a weak link in your audio chain.
