Sorry, I meant to say linear amplitude
.
Both are amplitudes of course, but decibels is a log ratio, whereas linear amplitude is just linear amplitude.
Anyways, yeah, you can use that thing for multichannel visualization. Just route multiple channels to it. There's a small tutorial on this page (although I should probably update it at some point):
https://github.com/JoepVanlier/JSFX
There's also a lua script in the repo, which is called LoadSpectrum. This automatically links every track that sends to master to the spectrum analyzer. If you're strapped for CPU cycles, I wouldn't do this though. Just route the ones you want to the analyzer.