What are Loudness Units/LU/EBU R128/K-system/LKFS/db RMS/etc?
All of the above mentioned are standards for measuring and calibrating loudness. Loudness in an audio signal is different than volume – volume may be the actual scale of signal power, but loudness is how loud an audio signal is perceived, which is a combination of volume, dynamic range, and such measurements over time. Because modern signal processing technology has made it possible to completely blast the loudness of a signal, certain international broadcast standards like EBU R128 and ATSC have been enacted to prevent huge variations in loudness between certain types of broadcast signals (primarily so commercials don’t shatter your eardrums when you’re watching a quiet TV program with the volume up). The K-system is a system developed by legendary mastering engineer Bob Katz (who quite literally wrote the book on mastering) that requires an engineer to first calibrate their playback system to a standardized baseline (c-weighted 85db per channel for a calibrated pink noise signal).
For more info, see http://www.tcelectronic.com/loudness/loudness-explained/