Setting the Mix
•
Turn down the amplifier gain before the system is first
switched on. This will avoid unwelcome howls of feedback
and can prevent loudspeaker damage due to switch-on
transients.
•
Set all the channel EQs to their flat or neutral position and
optimize the input gain control setting for each channel in
turn using PFLs.
•
If low frequency background noise is a problem, switch in
the High Pass Filter on each of the microphone channels
being used, except on low frequency sound sources such as
basses and kick drums.
•
Ring out the system as described above, with the vocal mics
open, and notch out any obvious trouble spots.
•
Establish the maximum working level for the lead vocal mic
so as not to incur feedback and then work a little below
this level to allow a margin of safety. Again, see the notes
on ringing out the system.
•
Set up the backing vocal mics and check that there is no
feedback problem when both the backing vocal and lead
vocal mics are on. If there is, reduce the master gain setting
until the feedback disappears.
•
Now the instrument and direct line inputs can be balanced
relative to the vocals. Start with drums and work through
to the bass and rythm instruments.
•
Test out any effects units connected to the system and
establish the correct balance of dry and effected sound.
Avoiding Feedback
•
Turn down or mute any mics not in use. This reduces the
risk of feedback and avoids the back line being picked up.
•
If feedback is a real problem, consider moving the main PA
speakers away from the mics a little. Also check the back of
the stage, because if the wall is acoustically reflective, some
sound from the room will be reflected back into the mics
increasing the risk of feedback.
•
Avoid excessive use of boosted EQ as this can encourage
feedback and may also spoil the basic character of the
sound. Consider it an aid to fine tuning rather than as a
means of making radical changes.
•
The use of stage monitors will also worsen the feedback
situation so run these at the lowest volume that the
performers can comfortably work with. Position the
cabinets so as to allow as little direct sound as possible to
enter the vocal microphones. If possible, use a graphic EQ
on each monitor.
NB: Remember, people soak up sound! The perfect mix achieved in
an empty venue will have to be tweaked when the crowds
arrive. Sound waves are also affected by heat and humidity.
SECTION 4: P
A
Mixing
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