The person running the mixer (what's the proper term?) had the level too low and changed it during the performance. It appears that he took four seconds to ramp it up.
The noise profile is different on the two ends, as shown in the graph below. The bulk of it reflects the volume change, but I have a constant noise source that doesn't vary.
After I use an envelope on the track, the volume and parts of the noise will match. But part of the noise will not match after the envelope is applied.
If I use one profile on the "before" part, and one on the "after" part, then I won't have covered those four seconds.
I'm thinking I'd like to first remove only the band of noise that does not change, across the whole track. Does anyone know how I would do that using Adobe Audition CC 2014?
(as an aside, the rough noise shape is visible by eye in any selection, even though other sound is mixed in. That allowed me to track his volume changes in the recording even though there was no intentional metadata. Interesting.)