AFW-1
Application Notes
What is the Anti Feedback Workstation?
Well, basically it is the best of both worlds!
Graphic Equalizers are great products, and are
extremely useful tools for professional audio engineers. But, they do require a fair degree of knowledge to operate them successfully.
Feedback Exterminators are great, too, because
they automatically find frequencies that are feeding
back and pull them down. But, that’s all they do.
You can’t tune the system with them - for that, you
need an equalizer, usually a Graphic Equalizer.
In the ARX AFW-1 Anti-Feedback Workstation,
we’ve combined the two products described above,
to give users the best of both worlds. An equalizer,
to tune the sound of the room/system, and an FBX
Anti Feedback to automatically pull out any feedback.
And, as a very useful added bonus, we’ve included a fast, smooth sounding Peak Limiter to ensure
that the signal stays within the level that you decide.
So, as you can see, although it may look a little
like a 30 band Graphic Equalizer, it's a whole lot
more. Since it involves a few radical departures from
the normal way that we think of equalizers, we've
put together these Application Notes to familiarise
you with the workings and the concepts behind the
ARX AFW-1 Anti-Feedback Workstation.
Let’s work our way through the operation of the
AFW-1, from start to finish.
The Equalizer Section
The EQ section of the AFW-1 has been designed without compromise as a totally accurate professional
third octave equalizer, with innovative ‘Constant Q’
circuitry. Constant Q is a true WYSIWYG (What You
See Is What You Get) design concept that allows far
more accuracy in EQ control.
Each of its 30 smoothly damped, centre grounding sliders can be adjusted to give a maximum of
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10dB cut or boost. The Q of the filter has been specifically optimised to allow easy combining of the
filters. This enables you to set up a musical, notch
free system curve.
It's quite possible to use this section as a standalone EQ, but then you'd be missing out on some of
the AFW-1's very exciting features!
Using the EQ section
The idea behind the EQ section is to ‘tune’ the room
to the system, and to ‘tweak’ the response a little so
that it sounds good. We’re not going to use it to notch
out feedback - we’ve got the Anti Feedback section
for that - but to adjust the overall sound of the system so it doesn’t sound ‘boomy’ or ‘harsh’.
So, play a tape or CD that you’re very familiar
with, and adjust the sliders on the EQ section so that
the system sounds ‘just right’.
Note that a little EQ is a lot, so use each fader
gently. Avoid any sudden dips or peaks - that’s not
what it’s there for. The look of the sliders should
resemble a smooth curve. If you don’t need to move
it, then leave it.
Avoid too much boost at lower frequencies. Very
few systems can deliver much response below 30
Hz, so it’s pointless pushing those sliders up. It will
only waste valuable amplifier power. However 50
to 100Hz can often benefit from a little boost, as can
8 – 12.5KHz. Between those points it should be a
smooth succession of gentle curves.
The Anti Feedback section
The Anti Feedback section of the AFW-1 is essentially a computer controlled parametric equalizer which
continuously searches for feedback. Once feedback
is detected, it extinguishes the feedback automatically by inserting a very narrow notch filter directly
on the feedback frequency, only as deep as necessary to control the feedback. It finds and eliminates
feedback typically in less than one second.
The result is that the overall program gain is increased 6 or more dB and provides much clearer and
more natural sounding speech and music. And since
it is fully automatic, no operator is required once it
has been set up.
The digital filters inside the AFW-1 are switchable between 1/5th octave and 1/10th octave. 1/5th
is recommended for speech applications, such as
conferences, speeches, etc, and 1/10th is recommended for music applications.
Important Note:
Before changing this switch, you must first power down the system. Then switch the filter to the
setting required. Power up the system again, and
during its turn on self test the AFW-1 will change
the filter setting.
The system should be RESET after doing this, by
following the Setup procedure detailed in the Owner's Manual.
About the Filters
The Anti Feedback section has two types of filters fixed and dynamic.
The fixed filters retain their frequency centre
points in memory until the unit is reset by the user.
These filters are set in the AFW-1 initialization procedure by the strongest resonating frequencies to
provide the system’s gain before feedback.
Dynamic filters control intermittent feedback that
comes and goes throughout the performance, such
as feedback from moving wireless microphones,
getting too close to speakers, monitors, that sort of
thing. They are automatically reassigned to new frequencies as feedback occurs on a first in - first out
protocol.
The Anti Feedback section circuitry has a total of
9 filters; 6 fixed and 3 dynamic filters. This has proven to be the best combination for most applications.
Where To Install The AFW-1 In The Signal
Path.
The AFW-1 can be placed anywhere in the system
that a line level signal is available. However, for most
purposes the best results are obtained if it is placed
last in the signal chain before the power amplifiers.
If you are using a 2 or 3 way or more system, with
an active crossover before the amps; or any kind of
speaker processor, then naturally the AFW-1 will go
before the crossover or processor.
The AFW-1 has Balanced Inputs and Outputs on
both XLR and jack connectors. On the XLRs, Pin 2 is
Hot (+). The jacks are Balanced TRS (Tip Ring Sleeve)
type, and are wired so the Tip is Hot (+), the Ring is
Cold (–) and the Sleeve is Ground. This means that
you can use whichever connector your system is set
up for, and you can also use the AFW-1 Unbalanced
if necessary. The latter is useful should you want to
use the AFW-1 as an Insert into a console channel.
The Limiter Section
The Peak Limiter in the AFW-1 has been included to
let you set an absolute ceiling on the output level.
Its attack and release times are program dependent and have been optimized to appear as transparent to the ear as possible.
However, remember that it is a Limiter, and
should be set at a level that coincides with the onset
of clipping in the system, where ideally it is not going to be active for the bulk of the time.
Setting up the system
As we mentioned before, the AFW-1 is a few radical
departure from normal equalizers. Its feedback suppressing filters are a lot more accurate in targeting
feedback than a typical 30 band EQ, and consequently the setup positioning is also different.
When’ringing out’ the
system, it’s best if you position the mics where they
would normally be during
the performance.
Because the AFW-1 filters target feedback frequencies exactly, there is no
need to point the mic towards the speakers as you
probably do with a normal
EQ.
The degree of ‘fail safety’ that you might need
with a normal EQ is much
less with the AFW-1. As a result of this the sound is
more natural, with less holes in it.
It’s also louder, since you haven’t pulled out as
much from the signal.
There is an extensive discussion of system setup
information contained in the AFW-1 Owner’s Manual. We strongly suggest that you read and absorb it
as it will make using the AFW-1 much easier.
We’ve also printed a shortened version of the setup procedure on the lid of the AFW-1, so if the manual isn’t handy, help is not far away!
FBX Feedback Exterminator is a Registered Trademark of Sabine, Inc, and
is the brand name of its line of automatic feedback controllers. Covered by US
Patent No. 5,245,665, Australian Patent No. 653,736, and Canadian patent No.
2,066,624-2. Other patents pending. ARX ® is a Registered Trademark of ARX
Systems Pty Ltd. All other trademarks are the property of ARX Systems.
ARX Systems Pty Ltd, Australia; Phone: +61-3 9555 7859 Fax: +61-3 9555 6747
Europe: ARX International; Phone: +44 (0)181 742 0350 Fax: +44 (0)181 742 0355
U.S.A: ARX North America; Phone:1-800-ARX-SYST (279-7978) Fax: 818 225 1309
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