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Reference Levels

Have you ever wondered why television commercials are always so much louder than the program? I always have to turn the TV down when the commercial break comes on and then turn it back up again when the program resumes. This is an obvious sign that reference levels are not being adhered to. If they were, the average level of all the program material on the television would be about the same and you would not have to constantly turn the volume up and down to maintain a consistent level.

The Purpose of Reference Levels and Tones

A reference level, or nominal operating level, is a measurement of the average program level of an audio signal. Obviously signals will go above and below this level in the course of a normal program, but the nominal operating level is used as a reference so that signals will be interchangeable between the different pieces of equipment, including broadcast systems, theaters, DVD players, and TVs. In analog systems, this level is measured using a VU meter. A VU meter is not a fast-reacting meter like the peak meters found in many digital systems. Extremely short transient peaks will not register on a VU meter and, therefore, it is important to realize that the actual level is exceeding the VU reading for very short peaks. The interesting thing is that human hearing perceives volume more like a VU meter reads audio signals. Watching a peak meter does not necessarily give an accurate reading of how your ear perceives the volume of that signal. It is because of this fact that VU meters are used to calibrate nominal operating levels.


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