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DN530
Operator Manual 37
Appendix D: Balanced/Unbalanced
Audio
Balancing refers to the type of input or output signal connections in an audio system.
These connections are specifically designed to reject external noise, such as from mains
wiring and internal interference from adjacent signal cables. Unlike unbalanced lines,
which are more susceptible to noise, balancing is especially useful when long cable runs
are used between pieces of equipment and can also provide other benefits, including an
increase in line signal level and a decreased possibility of ground loops. Balanced
connections are typically employed on long cable runs, such as to amplifiers, or for
cables carrying sensitive or low level signals, for example, mics. A balanced line
typically employs connectors of the XLR and 1/4” TRS jack plug types.
The basic principle of balanced interconnection is the cancelling out of any electrical
noise by means of a three-cable connection to achieve the required signal. Two of the
cables, called “hot” and “cold”, are used to carry signals, and the third is a grounded
shield that surrounds the hot and cold cables. (An unbalanced connection only has two
cables, one of which, the grounded shield, is also used for signal return.) As the hot
and cold cables are of equal voltage (and the same source impedance), but of opposite
polarity, when they are subtracted any noise voltages — caused by interference and
noise pick-up — appearing identically on both cables is cancelled out; the difference
between them being the resultant signal.
However, in practice the electrical noise on both cables will never be identical, and the
degree to which it is reduced is measured by the common mode rejection ratio (CMRR).
The electronically balanced input and output connections of the DN530 have the benefit
of high common mode rejection (CMR), which eliminates externally induced
interference such as mains hum etc. CMR is the ability of a balanced input to reject the
part of the incoming signal that has the same amplitude and opposite phase on both
input terminals, referenced to ground. As a specification, CMR is usually stated as a dB
ratio, called CMRR, at a given frequency.
Note: On balanced circuits, the ‘hot’ signal is also known as “+ve” and “in phase”, while
the ‘cold’ signal is also known as “-ve” and “out of phase”.