[Worship] How to Ring Your EQ Using A Compressor/Limiter

["Darcy L. Watkins" <dwatkins@xstreamworship.com>]

This is a sneakie little trick I figured out a while back that I thought
some of you may like.

As you know, ringing out your EQ can be a scary assignment and if the
feedback goes out of control, it can be really bothersome to others and
even hurt your ears.

The trick is to use the compressor / limiter for the following.
  1. To place a ceiling to the output volume of your feedback tone.
  2. To automatically adjust the gain for you as you tweak your EQ
settings.
  3. To measure the increased usable gain before feedback you get.

Most compressor/limiters have a reverse meter which goes from the right
to the left lighting up more as it reduces the gain by more.  (It's like
a backwards VU meter).  Typically to place it into limiter mode you need
to activate the hard-knee switch and crank the ratio dial hard over to
infinity (or "LIM") setting.

Place the limiter on you mains output after your graphic EQ but before
your cross-over and power amps.

Set up a good quality (close to flat response) microphone in the
position most likely to give you trouble (the pulpit location if
preaching is done through one of them gooseneck lectern mics).

Crank up the gain until the mic begins to feedback (be careful).  Then
use the limiter threshold to limit how loud this feedback can go.  You
should see the gain reduction kicks in.  You may notice the feedback
kicking in and out as the gain reduction quenches the feedback after
which there is nothing to gain reduce, so the gain goes up, then the
feedback kicks in again and this repeats.

Next boost the gain of the mic until the feedback is a constant tone.
If it gets too loud roll back on your limiter output dial so it is at a
desireable output volume level.

The output volume level should be loud enough such that background noise
doesn't skew any results, but soft enough neither to hurt ears nor
damage any equipment.  You should be able to walk around the room
without fear that something is going to blow up.

Next crank up the microphone gain.  You should notice that the volume is
unchanged but the gain reduction meter of the limiter changes as you
adjust the mic gain level.  Boost the mic gain sufficient to have the
limiter gain reduction meter light up the LED which matches (or nearest
larger setting) to what you have available on your EQ to reduce a band
by.

For my Alesis MEQ230, the available attenuation per band is 12 dB and my
nearest larger meter LED on my compressor limiter is 15dB.  So I would
adjust my unit so the meter shows 15 dB of gain reduction.

Your graphic EQ should have started flat or close to flat (sometimes you
boost areas that are lacking in your speakers and this will be the same
everywhere you set up).

Next you want to determine the frequency of the tone your system is
oscillating at.  If you cannot figure this out then determine the note
and octave on a keyboard.  Middle "C" is around 256 Hz.  Each Octave up
doubles the frequency.  Middle "A" is 440 Hz.  You should be able to
determine which slider on your graphic EQ needs to be adjusted.

Slowly pull the slider down.  You will notice that the gain reduction
meter reduces (i.e. in effect boosting the gain for you automatically).
Keep attenuating that slider until the feedback frequecy changes.  Take
note of how much gain you achieved.  For example if it was 7 dB out of a
total of 12, you have just improved your usable gain before feedback by
7 dB.  In my case there is potential for another 5 dB.  Take the EQ
slider you just adjusted and drop it to your max attentuation setting.
(In my case 12 dB).

Determine the new feedback frequency and find the EQ slider for that
frequency.  Pull it down until the first of either your feedback
frequency changes again or you have exhausted your remaining gain
reduction available.  If you exhausted gain reduction, the slider is
likely at what was left over after the last time round.  (In my case at
about 5 dB).  If your feedback frequency changed then take note of what
you have left this time and then boost attentuation of that slide to
what you had left the previous time, (for my example I had 5 dB left so
I would boost attentuation of that slide to 5 dB).

You then repeat this process until you have exhausted your gain
potential.

This technique appears complicated, but once you have the hang of it,
you can ring out any room in about 20 to 30 seconds.  Yes your eyes read
that right, 20 to 30 seconds.

After you have determined three to four notch points in a matter of
seconds, you can adjust some near by sliders to make the curve a bit
smoother.

You should then notice that you are able to crank up your gain by the
same amount as your attenuation potential of your EQ is (in my case 12
dB) before feedback starts.

Some things to keep in mind.  Only go for feedback elimination as needed
for you situation as overdoing it affects sound quality.  I was able to
elimiate feedback to the point where a preacher wearing a wireless lav
mic could walk right in front of the speakers.  His voice tone was
obviously altered (and it sounded very metalic as he walked infront of
the speakers).  For this unusual case, I had a dedicated 1/3 octave EQ
for that one mic but I used the same compressor/limiter trick to ring it
through.


Regards,

Darcy

-----------------------------
Darcy L. Watkins
dwatkins@xstreamworship.com
http://www.xstreamworship.com
-----------------------------


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