You've mentioned it a few times and today I downloaded the free version and plunked into my master buss. Exactly what I was looking for. I was about to buy something, one program was $200!! . I spent the afternoon tweaking 30 songs ( backing tracks) and added Span after the Brickwall limiter (set at -0.4db)  to my master buss. It allowed me to re mix the song on the fly while observing what was happening ,, ya, I mostly use my ears, but it sure sped things up and resulted in the 30 songs all being very close in RMS level and tonally balanced. Thanks Dave for another great freebie. 
 
http://www.voxengo.com/product/span/
 
 

Speaking of SPAN, did you know it could be used as a multi-track analyzer within Sonar or any other DAW?

Read my post, I put it on the Master buss, 
In the past I was using the LP multi band which would show me hot frequencies etc. This shows me that plus, it shows my Average RMS level ( real important ) and shows the brickwall limiter is doing it's job. 
 
If a song is not loud  enough I can deal with it track by track or, just push the mater buss input level until I'm where I need to be. I strive for -13 to -14  Average RMS depending on the material. 

Cactus. I knew what you meant, i just kind of went on tangent since we SPAN was topic. Just was pointing out another useful feature for the budget conscious. I have been using it in one of the studios I work in to overlay kick and bass at same time in SPAN. Didn't mean to hijack :)