I realise that you're looking for a computer based solution, but here's something I've been using myself lately. I used to have a Behringer DEQ 2496 digital EQ in my rack for
FOH. The outputs went south on me but the
unit has a true FFT analyser built in, so I hung on to it after buying a Driverack. Behringer also sells a calibrated mic, but you can use and calibrated (
flat response)
condenser as long as you know the input sensitivity.
At any rate, it sits in a 1RU rack on top of the dog
house of my Soundcraft now, with the mic pointed at the room. As an additional feature, I have a pair of
monitor outs, one for cans and one for a
wedge. I use the
wedge out, through an
impedance matcher into the left input and then anything I solo comes up on the analyser with the push of a
button. Once I have the room set up I just
switch over which inputs it's looking at and whatever I solo is displayed. Handy for tweaking
monitor mixes on the fly from 150 feet away.
Anyway, they're going on eBay for around US$250 used. The calibrated mic should be about another US$30. It's a
bit pricier than a software solution, but if your situation doesn't include a laptop it's worth a look.