All can be done separately for different channels.
Yes, that sounds almost like description of AudioLevel. See list of improvements below.
Examples of usage
Plugin has lots of options, but if you only want to make something pretty, then you will probably be happy with default values, so it's actually very easy to use.
Here are two skins: Spectrum analyzer and test skin, containing RMS, Peak, Waveform and Spectrogram Download:
Can be found in the archive with binaries.
Can be found on Github.
Comparison to AudioLevel
Plugin supports changing the majority of the options using !SetOption bang, but doesn't support because on each option change all values are reset!
Skin using this plugin should have low update interval. Best 16-17 ms. At most 100 ms. Otherwise some (or most) of sound values will be lost. It's a defense against too computations heavy options. I don't know yet how to make this more convenient.
Binaries and this Readme:
1.0 — initial release.
1.1 — list of changes.