[Boatanchors] OT: Question about audio

[W2HX]

Hello all,

I am in the process of building a new shack. I am hoping to do more AM than I used to, with more space for some nice sounding transmitters.  I thought it would be sensible to have some VU meters in the shack that I can route the audio to before heading to the exciters/transmitters.  The idea is to make sure I am optimizing the audio levels going into the exciters.  I plan to run my microphones through a pre-amp (Behringer Shark DSP110) to boost the level to line level (probably targeting +4 dBu balanced).  The transmitters I have will all accept "line level" audio at various selectable expected input levels.

The question is about VU meters. I have been looking on ebay and I've seen some things I don't understand.    I have seen some VU meters that have two types of meters on the same panel. One looks like the standard VU meter showing -20 to 0 and then +1 +2 +3 in a red section.  The other meter on the panel has the word "TONE" and "dB+Range" on it and the scale is -12 to +12.  

Just some examples on ebay of these kinds of meters.
331098964167
231107605604
281193957524

What is the meaning of these two types of meters? What do they mean "TONE"? 

Question #2.  I have read about a term called "Ballistic" and the options seem to be PPM or VU .  Is PPM something to do with peak vs. average? I know typically in ssb I would set my wattmeter to peak and in AM or CW I would set it to average. In an audio system, when would someone want to look at peak vs average? (and is that what ppm/vu means?)

Thanks very much for any input on this subject.
73 Eugene W2HX