Contents
Introduction: What is a VU Meter?

VU stands for “Volume Unit,” and a VU meter is a widely used analog audio level meter for level monitoring and mixing tasks in audio systems. The American National Standards Institute (ANSI) has standardized the VU meter as a measurement tool.
Human Auditory Perception and VU Meters
The VU meter is designed to reflect audio level changes at a speed similar to human auditory perception. For this purpose, the needle of the VU meter displays the average value over 300 milliseconds as RMS (Root Mean Square). This value was determined through clinical experiments involving numerous listeners. Often, this leads to the misconception that humans can only perceive sounds that last longer than 300ms. However, the general human reaction time falls between 150 to 300ms, and the shortest sound length that can be perceived is approximately 2ms.
Operational Levels and Calibration
In the VU meter, 0VU corresponds to a line level of +4dBu. Therefore, 0VU signifies the operational level in typical audio systems, meaning it is the most ideal level for equipment, often termed the “nominal operating level.” VU meters are mainly used for the calibration of various devices. This involves matching the nominal levels and is useful for setting up gain staging and gain structure.
Link to Nominal level document
Practical Applications in Recording
During recording, the VU meter is also used, and recordings are usually made to align with 0VU.
Display Range and Risk of Clipping
Generally, the meter displays levels ranging from -20 dBVU to +3 dBVU, taking 0 dBVU as the reference point. Areas above 0 are usually indicated in red, termed as the “HOT” range. Entering this range increases the risk of clipping.