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Audio Balanced & Unbalanced
Balanced vs. UnBalanced Audio Lines
Balanced lines use three wires with the outside wire being a shield around the
inside two. The inside two wires are thus shielded from external RF. The common
connectors for balanced audio is the XLR connector.
Unbalanced audio lines use just two wires, there is no shield. The signal passes
down the two wires unshielded from outside RF.
Home stereo connection cables are unbalanced line audio. The typical profes-
sional quality microphones use balanced line audio.
Balanced line connectors are XLR,
unbalanced line connectors are common to CamCorders and to stereo equipment
Unbalanced Audio
Most domestic audio equipment has unbalanced audio inputs and outputs. This
means that the audio output (left, right, or mono) appears on a single wire, and is
referenced to “0V” or “Ground”. Typical connectors used are RCA “phono”
connectors, DIN plugs/sockets, and 0.25" (6.3mm) or 3.5mm jack plugs/sockets.
Unbalanced audio is fine for the domestic environment, and for line-level signals
in a typical broadcast studio. Problems start to occur if the signals are being
carried over long distances, especially if the source and destination have
separate mains supplies.
Balanced lines
Balanced lines are different and a lot better. They use two signal conductors; one
carries the audio signal and the other carries an inverted copy of it. At the
receiving end, a special circuit takes the difference between the normal and
inverted signals. Any interference which gets into the cable is cancelled out
because it affects both signals equally.
Balanced cables have a screen too, but it plays no part in carrying the signal. If
the screen forms part of an earth loop, there will still be no interference.
