EBU R128, ITU-R BS.1770-2, ITU-R BS.1770-1, ATSC A85
These are important standards set to keep our sound levels consistent with other studios producing sound for film and broadcast. Far too often we take our frustration out on our remotes when a blaring commercial comes on or program material is too quiet. Its not so much the music but the dialog.
Consider the problems a broadcast station has when it gets recordings from a plethora of sources. Without a standard, the operator picks what he or she hears and sets your volume. Most technicians and engineers may not know to set the dialogue level for their analog services to 17 dB Leq (A) below 100 percent modulation for the typical set top boxes. While it is the subjective interpretation by the operator, there are devices we use to measure this phenomenon that give us a way to be consistent in what is truly perceived levels.
The same goes for the theater. There are standards set that every studio needs to conform to when mixing sound for picture. If you want a good sounding audio track, seek out a studio that has the ability to conform to these standards.
Sometimes a simple adjustment to the mix will correct a poorly mixed film. It is too often that no consideration is given to the sound until it is not there. Don't loose your target audience with a bad mix.
Later I will go into theater standards. ITU and NAB will refer to LKFS values. These are loudness managements needing special metering. This applies more to broadcast (ITU1770-2) or theatrical trailers (TASA).