The AFS Advanced Feedback Suppression processor was designed to provide state-of-the art feedback elimination processing, while maintaining a simple and intuitive control interface. From the powerful DSP module to the no-nonsense user interface, the AFS provides all the processing and control necessary for both installation and live use. The AFS is an absolute must for any live sound application. Ten and twelve filter feedback elimination processors have become the de facto standard, but the engineering staff at dbx have never been quite content residing in the neighborhood of the status quo. To achieve these staggering numbers dbx utilized their patent-pending AFS technology that had previously only been available in the upper echelon line of products and made it available in this stand-alone processor, which takes all of the guesswork out of feedback removal.
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I remember when automatic feedback suppressors first appeared and were hailed by some, including me as a wonder of their age. Imagine having an invisible, unpaid extra pair of ears and hands constantly monitoring the PA for feedback problems and instantly applying selective EQ corrections as necessary, all without interrupting the performance or affecting the overall sound quality It all sounded too good to be true at the time, but it actually worked pretty well in many applications, and the detection algorithms have now evolved and become increasingly sophisticated.
As a user of the previous model myself I was interested to have a look at its replacement in the product line. I like to have a feedback processor available for every job I do, in the same way as I like to have extra sets of batteries and every kind of mains power adaptor — I may not use them every time, or even all that often, but every so often a situation will arise where that extra capability can make all the difference between a horrendous, stress—filled experience and a successful result.
Much has been, and will continue to be, written about the reasons for and against using feedback processors, but I have always regarded them simply as automatic outboard EQ designed with a particular task — the control of feedback — in mind.
With the AFS2 the team at Dbx have essentially taken the existing functionality of the AFS processor and developed new detection and control algorithms, along with an enhanced degree of user control and the ability to save and recall settings. In brief, the AFS2 has the ability to detect when feedback begins to occur at any particular frequency, and will insert a sharp notch filter into the signal path at that frequency. You could think about the two types of filters as addressing different aspects of a live show, in that fixed filters are addressing major issues relating to the venue and stage layout, and live filters will cope with anything that happens post—soundcheck, such as increasing monitor levels, or physical changes like singers moving around close to monitors, or even taking the mic out front so that the audience can assist with the choruses!
The huge advantages that the AFS2 offers over manually applied EQ — including traditional graphic equalisers — is that the centre frequencies of the filters are calculated to be at exactly the required frequency. Consider what a traditional third—octave filter actually covers in terms of a musical scale! The AFS2 does allow different filter types to be set for different filters — if you change the setting, it will only apply to new filters without changing any already set.
First off, the AFS2 is a well—built unit, with a neat and sturdy steel single-rack case, and the front and back layout is practical, simple and neat.
There are cooling vents on top above the power-supply area and at both sides, but no fan. Feedback processors suppressors, eliminators, destroyers — whatever the makers prefer to call them are functionally fairly straightforward and have but one goal in life, which is to detect and control unwanted audio feedback.
The AFS2 has two inputs and two outputs, which can be used independently or in linked stereo mode. A new feature of the AFS2, compared to its predecessor the AFS, is the provision of a USB socket for applying firmware updates — generally a comforting sign that the model will be staying in the current product range for a good long time, as new features and upgrades can be applied without replacing the hardware.
The front panel is neat, simple and effective, the traditional rows of filter LEDs and dedicated button array complemented with a small LED display screen and rotary selector, similar in size and style to those found on the 1U DriveRack models. The two horizontal rows of red filter indication LEDs are large and bright, and easily visible from several meters away.
The setup wizard first asks if the unit is to be operated in linked mode, where the same settings and filters are applied to both channels, or as two completely independent processors for example when used on bus or channel inserts , in which case you have to go through the wizard twice. Once that little formality is out of the way you can get on with the actual setup, which guides you through every step and is very easy to follow.
I like this feature as I know of several potential users of this unit who would appreciate this level of hand—holding. The wizard then reminds you to bypass any active noise gates, and fully lower the main mixer outputs. The next step is to choose how many fixed and how many live filters will be used, and to make things simple the wizard asks if it should set the default number of 12 fixed filters.
When the fixed filters have been set and confirmed as all done, the AFS2 switches on the live filters, which will swing into action when feedback is detected from that point on. The live filters behave in a different way to the fixed set, and are designed to differentiate between sustained musical notes and unwanted feedback.
I connected the AFS2 into our rehearsal studio PA and went through the setup wizard with four open mics to see both how effective the feedback reduction was, and what effect it had on the overall sound. I used the default setting of 12 fixed filters and, as expected, I could set a significantly higher level in the room with the AFS2 than without it.
I tried connecting the unit as an insert and in line between mixer and powered speakers, and I found no noticeable difference in performance between the two setups; the AFS2 seemed to be tolerant of varying input levels, although the manual sensibly recommends using inserts as these will deliver a suitable and fader—independent drive — so long as you have a couple of input-meter segments lit up it should work happily.
The increase in available volume was impressive, and even with all 12 fixed filters set the resultant sound was fine. The other thing I noticed about using the AFS2 was that even at volumes well below the feedback threshold, using it made the PA sound better, as all the worst excesses of the room response had been filtered and the result was a cleaner, clearer output.
Our rehearsal hall for my 21—piece band is a bit of a nightmare for live sound, especially with no audience in place, so I tried the AFS2 on our vocal mics and was very impressed with the results. I used one channel of the AFS2 on mono mains and the other on a single floor monitor just in front of the two singers, and not only was it possible to achieve much louder levels, but by pushing the volume during setup to force the system to ring out the worst frequencies, the whole sound became more pleasant, cleaner and less fatiguing.
A neat feature is the ability to look at the main parameters of all the filters in place — a single press of the data wheel displays a representation of where they all are across the whole frequency range, and their individual information is displayed as each is selected with the wheel, so you can see exactly what the AFS2 is doing for you! Various stand-alone products with similar overall functionality are produced by manufacturers including Sabine, Shure, Peavey and Behringer.
The AFS2 is easy to use, especially with the setup wizard, and buys you considerably more level before feedback sets in, without drastically altering your sound.
Alternatives Various stand-alone products with similar overall functionality are produced by manufacturers including Sabine, Shure, Peavey and Behringer. Pros Good setup wizard for inexperienced and occasional users — no manual necessary.
Good live filter discrimination between music and feedback signal components. Very narrow filter widths available. Fast and reliable in operation. Flexible operating modes. Great filter parameter display screen. Summary The AFS2 is easy to use, especially with the setup wizard, and buys you considerably more level before feedback sets in, without drastically altering your sound.
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DBX AFS 224
dbx AFS 224