INTERfACE WiTH Sub-MixERS

Larger mixing consoles, and
sometimes smaller mixers, often have
sub input, link or expander connections.
Such connections generally apply
line level signals directly to the main
program mixing busses, and sometimes
are also provided for auxiliary busses
(echo/effects, cue, etc.). They are
intended to permit another mixer or
mixing console to be electronically
joined so that both units' inputs can be
combined onto the same busses, and
controlled with one set of master
faders. For convenient reference, the
main mixing console may be called the
master, and the sub-mixer the slave in
such setups.
The concept of sub-mixing is not
new, and it continues to offer benefits
in a number of situations. No matter
how large and complex a mixing
console, it seems that there are times
when just a few more inputs would be
helpful for a particular job, and this is
where the sub-mixer (or subsidiary
mixing console) is ideal. For example,
it may not be economical, or the
physical space may not be available, to
install a larger console to handle the
occasional need for a few additional
input channels. Sometimes the submixer
can be used to mix a separate
stage act, or to mix only the electronic
keyboards, which provides local control
for the person concerned with that
group of inputs. Then these pre-mixed
inputs are fed to the main mixing
console for distribution to the sound
system amps and loudspeakers. It may
be that a rental sound company wishes
to keep maximum flexibility in their
inventory, and would prefer to stock
two 16-channel consoles, which can go
out on separate jobs sometimes, and be
linked to create one 32-channel console
on occasion, rather than carry a single
32-channel console that can only be
used for one job at a time.
The sub-mixer inputs on a console
are generally specified to accept one of
a few standard line levels, typically
-20 dBu (78 mY), -10 dBV (316 mY), or
+4 dBu (1.23 V) nominal. In most cases
there are no input level controls on the
sub-inputs, so those levels must be
controlled by the master faders on the
sub-mixer. So long as the impedances
and levels are in the right range,