Owner`s manual

85
The above nominal levels represent typical or average levels that are often
exceeded when recording loud signals such as drum beats. The difference
between the nominal level and the loudest signal that can be recorded without
clipping is called “headroom”. Your Echo card provides approximately 14dB of
headroom allowing an 18dBu signal to be recorded.
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 card 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). Gina24 will also
accommodate the two conductor unbalanced style connector.