Owner`s manual

converting dBV levels into dBu levels is as simple as subtracting 2dB (2.21
to be exact).
Signals are also occasionally represented with units of dBm. This is an older
unit that measures power instead of voltage levels with 0dBm representing 1
milliwatt. Earlier tube-based audio equipment used standardized input and
output impedances of 600 ohms, so a 0dBm signal was produced with a
voltage of .775 volts. Since most of today’s equipment uses impedances
other than 600 ohms, it is more useful to represent signals by voltages rather
than power and the dBu unit was introduced. A signal level of 0dBu is
identical to a level of 0dBm.
Digital signals, after they are recorded, no longer directly represent any
physical quantity such as voltage or power and 0dB is generally used to
represent a “full-scale” or maximum signal level. All other signal levels are
lower and are expressed as negative decibels. Most meters on digital
equipment have 0dB at the top and range downward from there. A signal
that is 30dB below full scale would simply be referred to as a –30dB signal.
Nominal Signal Levels and Headroom
Today’s equipment is generally referred to as +4dBu equipment
(professional) or –10dBV equipment (consumer). These levels are the
typical or “nominal” signal levels you can expect to see with professional
(studio) equipment such as mixers or with consumer equipment such as
home stereos and CD players. A +4dBu signal has a voltage level of 1.23
volts and a –10dBV signal has a voltage level of .316 volts.
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 hardware provides
approximately 14dB of headroom allowing an 18dBu signal (9.8 volts or 28
volts peak to peak) to be recorded.
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