loudness/frequency analyzer tool

[Jeff Fortin Tam]

I would like to be able to have an analysis dialog that, for the current selection, displays the frequencies and their loudness on a curve. The primary use case for this would be
1) figure out on which frequencies there is constant noise
2) someone like me who records sound samples and wants to compare their loudness; in my case, for example, I recorded samples in the backyard of different houses, and I would like to be able to compare the amount of ambient noise coming from a nearby highway.

Bonus points for being able to actually put a curve in there and lower/raise certain frequencies, but I guess that would be a separate plugin/tool.