by Jon Chappell

The concept is inspired: An inline device that automatically senses feedback and squelches the offending frequencies without coloring the sound. No more stuffing the holes of your acoustics and semi-hollows with foam, no more nervous soundman riding your gain. How would such a device operate and would it really work?

Sabine has proven that through the use of filters (narrow-band frequency attenuators) they can provide effective feedback elimination with virtually no loss of signal power or signal coloration. And best of all, they've made it affordable and easy to use. If you play in many and varied live situations, and use instruments that are prone to feedback, the FBX-SOLO just might save your (professional) life.

The FBX-SOLO SL-610 Feedback Eliminator automatically senses the feedback's pitch (frequency) and unleashes one of its six micro-filters to attenuate - or cut back - the offending frequency. It does this in typically less than one second (.4 seconds @ 1 kHz) . The filters are quite narrow - 10 times narrower than the sliders on a 31-band equalizer (the device usually used for corrective EQ). This ensures that only the offending frequency is cut (there's too much of it, or it wouldn't be feeding back), leaving the surrounding frequencies untouched. What's more, some of these filters are dynamic, not fixed, which means they can track feedback as conditions change.

The FBX has both fixed and dynamic filters. Fixed filters are determined at setup time automatically and remain there until a reset is performed. The dynamic filters chase intermittent feedback after the initial filters have been set. Setting up the fixed filters beforehand allows you to have a much louder signal before feedback occurs. The dynamic filters are there for the unpredictable results that can't be anticipated in a soundcheck. Sabine gives you any combination of six filter algorithms. If you want maximum gain before feedback, use the first setting. If you're going to be walking in front of the speakers and generally creating a variety of feedback situations, use the second setting. You can use the FBX-SOLO with either a mixer or an amp.

Setting up the FBX-SOLO for a particular environment resembles the procedure I used to go through when "tuning a room": turning up the gain until a feedback point occurs, measuring that frequency with a frequency analyzer and then pulling back the slider on the 31-band graphic whose frequency was closest to the one on the analyzer. The FBX operates in a similar way, but with two improvements: (1) It reads the feedback frequency and adjusts for it automatically, greatly speeding up the analysis process; (2) its "slider" is narrower (trashing less of the surrounding, unoffending frequencies) and not fixed - it goes right to the exact frequency, not just near it. Once you're used to this procedure, it takes only one or two minutes to get the FBX up and running. When you shut the power off, the FBX remembers your last settings.

I devised an ingenious (if I do say so myself) test where I split my acoustic guitar's signal into two paths and sent them to separate mixer channels. One channel had the FBX-SOLO in-line. Then with my MIDI sequencer I sent randomly timed program changes to my multi-effects processor. The processor was set up with identical programs except for the EQ. The different EQ settings were employed to simulate what might happen to an acoustic environment as it changed - filled up with people, got muggier, endured a bass player who got increasingly louder as the night went on, etc. Then while the sequencer played - sending program changes willy nilly - I played my acoustic while A/B'ing the individual mixer channels at will. I'm happy to say that as I was able to coax feedback out of the non-FBX channel, switching to the FBX-enabled channel eliminated the feedback virtually instantly. Similarly, playing the entire passage on the FBX channel produced no feedback at all, and did not color the sound.

The FBX-SOLO works well for guitars. It's faster and more accurate than a soundman, and does its work transparently. And it won't spill a beer onto your mixer as it lurches over to pull your fader down.

Contact:

SABINE
13301 Highway 441
Alachua, FL 32615-8544
Phone:
(386) 418-2000
fax (386) 418-2001