FRONT OF HOUSE
UNDERSTANDING LEVELS | Kent Morris
Levels are what keep a sound system rolling. 3. Maintaining line level within the console was and truly horrific in digital. The idea, especially
From the lowest -60dBV of a microphone straightforward in analog days. The idea was in the digital domain, is to get as close to FS as
through the 0dBV of the mixer to the multiple to establish the input at a volt through gain possible without going over the edge. This is
volts of an amplified loudspeaker, everything on the pre-amp and then maintain that level due to the way digital works. At low levels, the
is about level. For decades in analog audio, through outboard processors and equalizers resolution is low, but increases quickly as the
there have been standard parameters in place and deliver it to the power amp where it would level is raised. A good dynamic range controller
across all platforms, making interconnectivity be multiplied. Confirmation was as simple as can do wonders to keep the signal hot, but
possible, if not always simple. Digital audio, hitting the bypass button on, for instance, the below the redline.
though, has brought a new set of issues to the graphic EQ and adjusting the unit level until it table, including a re-think of Full Scale, which was the same in both switch positions. Digital 5. Power amps are not what they used to be. In
must be addressed in a different way. Here are is more difficult as the gain is not intuitive as it is the old days, classic A/B topology delivered a
some thoughts on how to best implement level with analog circuits. Most digital paths include few hundreds watts of solid, consistent power
in several common scenarios: a digital trim to act as a fine tuning mechanism to the speakers. The amps were heavy, drew a
for the coarse adjustment residing in the lot of power from the wall and were often noisy,
gain knob. but they worked in every environment. Current
1. Mic level is quite low, on the order of a few
ten-thousandths of a volt. Any noise in the amplifier technology, usually Class D, is based
microphone’s electronics will be amplified around digital circuits and fast-acting switch-
along with the signal, so use the cleanest mic
available for critical applications such as grand
piano, solo violin and lead vocal. The mic pre-
amplifier in the mixing console raises the low
mic level significantly, to roughly one volt, or line
level in deference to old telephone line levels,
which hovered around one volt. Essentially
every part of the signal chain aside from mics
and power amps is line level.
2. Since the mic pre-amp increases the mic
level a thousand times, its performance has
a dramatic impact on the overall sound in the
system. Modestly priced consoles have to
allocate limited financial resources to every
component and sometimes the mic pre is
The easiest way mode power supplies that, while lightweight
to remember than ideal power supply situations. Modern
the process is
to “get gain
and efficient, can be finicky when used in less
amps generally do not do perform well bridged
or at two Ohm loads, but the need for these
measures is eliminated by the vast increase in
output power afforded by Class D. On all power
amps, get and maintain proper line level to the
input and then increase the adjustment control
early and get
noise late in the
on the power amp only until the desired speaker
output is achieved. Since noise increases with
sensitivity, having a strong input level means
less noise on the output.
Good live sound falls to setting the optimal
chain.”
mic, line and speaker levels. The easiest way to
short-changed. In that case, it may be wise remember the process is to “get gain early and
to invest in a quality outboard mic pre-amp get noise late in the chain.”
for the primary channels. While prices can be 4. Full Scale, as its name implies, is the point
astronomical for studio models, good dual- at which the system has been maximized. In
channel live units can be purchased for a few analog, it is where the rails are met and in digital
hundred dollars. it is when magnitude has reached its top value.
Beyond FS lies distortion, unpleasant in analog
154
January 2019
Kent Morris
Kent is a 40-year veteran of the AVL arena driven by
passion for excellence tempered by the knowledge
digital is a temporary state.
Subscribe for Free...