A brief explanation for the logic behind the metering variance between analog and digital devices should help to clear up some of the confusion this subject generally engenders. Digital devices do not have a standard "0 VU " level setting that would directly correspond to a nominal input or output level. The metering of digital devices are deliberately calibrated for a "zero" level to be several decibels (typically - 18dB) below peak level or digital clipping. The reason for this amount of level before clipping (headroom) becomes readily apparent the
first time one encounters the audible result of over-saturating a digital recording device. The end product of this digital clipping is as unpleasant to hear as it is unacceptable. Therefore, headroom in the digital environment is provided below " zero".

Analog recording is a different experience, entirely. Not only is a small amount of over-saturation acceptable, it is often desirable. Tape compression that occurs by recording drums at elevated levels, for example, makes these percussion instruments really come alive. The nature of the behavior of analog recorders allows analog devices to provide headroom above "zero". Thus, a "zero" reading on an analog device still provides headroom
before an unacceptable level of signal distortion occurs. This is explains the very radical difference in the meter calibration of analog devices which provide headroom above "zero".