Balanced Audio Connections
There is a general trend by high-end audio and AV equipment manufacturers to utilise the common mode noise rejection benefits of balanced interconnects. So what constitutes a balanced audio signal and why is their use becoming more prevalent? Hopefully the following explanations will make thinks a little clearer.
Balanced Audio employs a cable and electronic configuration capable of minimising unwanted noise from interference in audio cables by benefiting from the noise rejection characteristics of a screened twisted pair cable. This is based on the principle that two identical signals which are inverted 180° out of phase will cancel each other out. The cables used in such systems are designed to carry two versions of the signal and manipulate the relative phases of these signals to eliminate noise.
In order to fully understand the principles involved, it is perhaps logical that firstly we consider the traditional unbalanced RCA type connection. By far the most common cable format used for unbalanced interconnects is a coax whose basic construction is shown below. The central signal wire is surrounded by a screen that acts as the zero volt reference. Connections are predominantly of the familiar RCA-type but 1/4" phono jack connectors are supported by some manufacturers. and the RCA connector. However any single-pin connector used for audio is unbalanced.
Balanced audio cables employ two signal conductors or cores often referred to as a hot (positive), cold (negative), in addition to a screen that is used as an earth. This screened twisted pair cable construction, (as used in the Brilliance Purity and Symmetry interconnects), can be seen in the above image. The audio signal is transmitted on both the hot and cold lines, but the voltage in the cold line is inverted so it is negative when the hot signal is positive. These two signals are often referred to as being 180 degrees out of phase with each other where one signal is effectively flipped upside down.
When the cable is plugged into an input on your audio equipment such as an amplifier, the positive and negative signals are summated. You would anticipate that the two signals would cancel each other out, but at the input stage they are put "back in phase" (i.e. the inversion is reversed) before being summated.
So why is this so ‘revolutionary’? Well along the length of the cable, noise can be introduced from external sources such as power cables, RF interference, etc. This unwanted noise will be the same on both positive and negative conductors so when at the input stage when the inverted audio signal is flipped, the unwanted noise on the second conductor is inverted, and when the two signals are summated, the two noise components effectively cancel each other out.
Balanced audio connections because of the two signal conductors require termination using 3-pole plugs and sockets and the standard connector for balanced audio is the 3-pin XLR. There is no official standard for wiring balanced audio cables, but a the most common configuration is:
Pin 1: Shield (Ground)
Different plug types are generally employed at the transmitter and receiver ends with female plug at the source and male at the other. One of the most prominent suppliers of XLR plugs and sockets is Neutrik, whose products you will find used for all Brilliance balanced cables whether it is the Purity digital or Symmetry analogue type.
There are two basic forms of signals that employ the balanced topology, namely digital and analogue. The latter is very similar to standard audio applications but with the differenced as outlined above but fir digital links, the differences are slightly greater.
AES/EBU (Audio Engineering Society/European Broadcasting Union) is the name of a digital audio transfer standard. The AES and EBU developed the specifications for the standard. The AES/EBU digital interface is usually implemented using 3-PIN XLR connectors, the same type connector type as described above. One cable carries both left- and right-channel audio data to the receiving device.
AES/EBU is an alternative to the S/PDIF standard with an impedance of 110 Ohm employed rather than the 75 Ohm as employed by the S/PDIF. There are other fundamental differences in the digital protocols employed therefore the two signal types are inherently incompatible.
More information on our range of AV interlink cables including digital interconnects, RGB component video leads, RGBS / RGBHV projector / HDTV cables, composite video interconnects and multi-channel audio cable sets can be found on our AV Interconnects page.
For our complementary range of Prodigy single and bi-wire speaker cables with a choice of Profigold¹ banana plugs or Ixos spade connectors, please see our speaker cable page.
For details of our home audio cabling solutions please see our Audio interconnects page.
¹Profigold is a registered trademark of Profigold Cables.
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