7.2.4.1 The Mix Matrix In General SoundReinforcement
Instead of feeding the house sound system directly
from the Group outputs [130], or the Stereo output
[133], the sound system can be fed from the Matrix
outputs [131]. The Group busses and Stereo bus would
then be used for mixing sub-groups of different sources;
i.e., brass, drum/percussion, lead vocals, backup vocals,
rhythm guitars & bass, lead guitar, keyboards (in
stereo), and so forth. The Group Master Faders and
Stereo Fader would control the overall level of each sub-
group of input channels. The matrix channels can be
used to create four stereo or eight mono mixes from
those groups. The mix matrix outputs then feed the
power amps and speakers for various zones in the main
house, as well as other areas (dressing rooms, lobby,
remote feeds, etc.)
The advantages to this approach are numerous. For
example, if the brass level is too high in all outputs, only
one Group Master Fader need be adjusted (for the brass
subgroup). On the other hand, if there is too much vocal
near the front of the audience (due to spill from the
vocal stage monitors), you can adjust the one matrix
mix level control, corresponding to the vocal Group, in
the matrix channel that feeds the near-stage house
speakers. Similarly, if your system is designed with
larger speakers near the front of the house, having
better low frequency output than the rear fill speakers,
then those speakers should be fed the bass-heavy
instruments. By adjusting the matrix mix level controls
for the drum/percussion and bass guitar Groups so that
more of these subgroups goes to the matrix outputs that
feed the near-stage speakers, and less to the rear fill
speakers, the overall sound quality in the house will be
improved.
For program fades, you have a choice: you can use
the Group Master Faders, in which case the previously
established balance for each zone of the sound system
reappears as soon as these Faders are returned to their
correct settings. Or you can use the MTRX MASTER
controls, in which case the previously established
program (group) balance remains, but you’ll have to
recreate the zone-to-zone balance when you bring up
the MTRX MASTER controls. Of course, you can always
use the Group ON/off switches [45] or Matrix ON/off
switches [34] to mute the output to the speaker system,
thereby eliminating any uncertainty in re-establishing
program levels.
If the PM4000 internal slide switches are reset so
that the Group-to-Matrix and Stereo-to-Matrix feeds
are derived pre-fader (as described in Sections 6.12 and
6.13), then the Group and Stereo Master Faders will not
affect the matrix mix levels. In this case, the matrix can
be used in much the way, to create the necessary
mono or stereo house feeds, while the group and/or
stereo outputs can be mixed independently to feed a
multitrack tape recorder. Whereas the signals applied
to tape are generally recorded at a uniformly “hot” level
(high enough to optimize signal-to-noise ratio, and just
low enough to avoid saturation), the same group signals
can be mixed to achieve the desired program balance for
the live sound presentation. If some sort of group
control is needed which affects both the “recording feed”
from the group outputs and the “house feed” from the
matrix, the VCA Master Faders can be used.
7.2.4.2 Using The Matrix Sub InputsFor Effects
The eight MTRX SUB IN connectors [110] on the
rear panel apply signal directly to the correspondingly
numbered MTRX SUB IN level controls [30] on each
matrix channel. Since a different signal can be applied
to each matrix channel, SUB IN is the only matrix
control that is not fed in common across the eight
matrix channels from a single bus. One application for
these inputs is to mix an effect return into the matrix
output, but not into the Group or Stereo outputs.
Consider, for example, the situation described at the
end of Section 7.2.4.1, where the Group outputs are
feeding a multitrack tape recorder, and the house sound
is fed from an independent, pre-Group and pre-Stereo
Fader, matrix mix. If the “house” were actually an
outdoor stage, the sound could possibly benefit from
some added reverberation. It would not necessarily be
desirable to add that reverberation to the Group or
Stereo mixes, however, since these mixes are being
recorded “dry” for subsequent remixing, where the
effects requirements are likely to be different. The
solution is to use one (or more) Aux sends, or even a
spare matrix channel or two, to create the necessary
effects send mix. Then apply the return from the effects
unit(s) to the MATRIX SUB IN connector(s) which feed
those matrix channels that are feeding the house mix. If
necessary, use a signal splitter (a splitter transformer or
simply a “Y” cable) so that a single effects unit output
can feed two or more matrix channels. In this way, the
live sound will be “wet” (include the effect), but the
recorded sound will be “dry.”
7.2.4.3 Other Uses For The MatrixSub Inputs
If a stereo or 4-track recording is to be played during
intermission, or even as an adjunct to the live program,
it is not necessary to “use up” input channels or effects
return inputs for the tape. Instead, the tape recorder
outputs can be connected to the MTRX SUB IN, mixed
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