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Unbalanced and Balanced Inputs and Outputs
An unbalanced signal, commonly used for guitars and consumer electronics,
contains two components, a ground signal and a “hot” or active signal. The
ground is the barrel of a ¼” connector and the shell of an “RCA” style
connector.
A balanced signal contains two active signals instead of one in addition to
the ground. These are referred to as the “plus” and “minus” signals. A
balanced input amplifier amplifies the difference between these two signals.
Any extraneous noise picked up from power lines or other sources will
appear equally on both the plus and minus inputs. This is called “common
mode” noise since it is common to both signals and the input amplifier will
subtract the noise on the minus input from the noise on the plus input.
If the input amplifier is perfectly balanced and the noise on both plus and
minus is precisely equal, the noise will completely cancel out. In the real
world this is not the case and some of the common mode noise will still
make it through, although at a much reduced level. How well an input
amplifier rejects this common mode noise is called the “common mode
rejection ratio” (abbreviated as CMRR) and is expressed in dB.
Balanced signals connect with either XLR connectors or TRS (tip, ring
sleeve) connectors. Your Echo hardware uses TRS connectors for
connecting balanced line level signals.
The three sections of a TRS connector are used to transmit the three
components of a balanced signal (T = plus, R = minus, S = ground). Your
Echo hardware can also accommodate the two conductor unbalanced style
connector.