Audio Systems: wireless mic feedback, dsp filters, wireless mic

Question
From time to time, I see a singer with a wireless mic walk off stage out into the audience or walk down what's called the "cat walk"  in front of the main house speakers with no feedback!!!  How is this done?

Answer
Hi Richard and thanks for the fine question.

It is called an Automatic Digital Feedback Eliminator (ADFE) and they are not cheap ($1900.00 and up) but they allow a singer or a spokesperson to do their thing with only the house PA. This way, the speaker or singer can hear exactly what the audience is hearing since the PA speakers can be placed behind them (and even behind the band). There is often no need for monitor amplifiers, a monitor sound technician, monitor mixing boards or speakers in this situation. That said, the ADFE can be 'affordable'.

Following the A-D conversion at each input, the signal often passes through multiple DSP filters, the ADFE (automatic digital feedback eliminator), a compressor and a digital delay.

Example:
http://www.pro-sound.com/W/SLECDM812.html

Of course, they could just be lip-syncing. ^^

Cheers,
JM