[Five]

dynamics processing can affect the RMS (which is the percieved volume)

human ears naturally compress sound so that at the concert when your ears are getting hammered with high SPLs they sort of "turn down" the volume and take some time to return to normal.

if it is analog it could be tape compression and a more narrow dynamic range

well there's a few theories for you. you can't really record a show with a 150dB range and expect it to translate perfectly as tho you were there.