There are many ways to achieve high sound pressure level. The equipment’s output level, speaker’s efficiency, speaker’s quantity, and the space of your room, all have impact on measured volume loudness. I can simply install multiple center channels each equipped with a 99db 1W-1meter high efficiency woofer, with 10db gain boost into each channel and measure it in my small bedroom; it will definitely louder than 85db. However, if I move this set-up into another larger bedroom and measure it again, the sound pressure level changes considerably.

Also, there are very few standard practices in studio mixing. People tend to move levels and headroom around to suit the tastes of the particular producer and these preferences often flow through the final product. This is particularly noticeable if you load a rock-n-roll CD and follow it with a classical CD in you’re the CD player. You will find yourself reaching for the gain control, as the differences in digital operating level often exceed 20 dB. Same thing apply to DVD remixing.