Appendix C: 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
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 DN540 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
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