Since none of the native Linux spectrum analyzers quite do it for me, I thought I might mention this free Windows VST analyzer. I've used this one for some time now and really like the easy to see what's going on aspect with it. Top line is peaks, bottom line is averages, and bars are realtime. The 1.09 beta runs fine on wine-staging here.
https://sevenphases.wordpress.com/spectrum-analyzer/