The Guardian posted this article about an anti feedback device for use in concert sound. As if it was some kind of new technology.
Hate to rain on your parade, guys, but this is hardly new. In fact, anti-feedback technology has been around for years in various forms – just no pro with any sense uses it.
Here’s a basic concept for a digital anti feedback device that I’ve come up with in the past after looking at the responses of commercial devices/software; it might go something along these lines:
- Transform signal from time to frequency domain (through FFT or similar)
- Perform a second transform on frequency blocks (say, 100Hz-500Hz), fit and differentiate the curve
- Using this value you can then set a threshold so that if overall level of a given frequency is rising too quickly you can then go and compress that frequency block using the compression curve of your choice.
If you think this sounds familiar, this is more or less how an multiband compressor works. You can in fact construct an “anti-feedback” device from a multiband compressor, if you put in the right settings. If you wanted to get fancy, you could throw in reverse gate to knock out extreme conditions.
There is a big issue with such devices – they take the control away from the engineer. Sound engineers are control freaks; and for good reason. As soon as you start automating things, you lose control: this isn’t good for the performers or the audience. All of a sudden you’re not listening to the performance, you’re listening to a machine.
And, really, feedback is something you eek out of a rig at a very early stage – if you’ve not done this then your rig isn’t set up properly. Sure, the best sounding PAs are usually teetering on the edge of feedback – and the engineers are taking a risk to make it sound that good. If you are really that scared about feedback then you tune the rig more conservatively.
For environments where you are very concerned about making the PA transparent as you can (say in opera (sound engineers are about as welcome in opera as chemist at a homeopathy conference)) then the last thing you want to do is start letting machines mess with the output.
In a non pro environment I can see it having it’s uses. For example, in a home studio, it would be beneficial to have a conservative feedback detector to mute your soundcard/amplifier if it detects feedback (as well as notifying you about this). This could well save your speakers. But for live music? No.