VU (Volume Unit) Meter
A VU meter responds in a fashion very similar to how human ears perceive loudness. A true VU meter uses a decibel scale, and is carefully ballistics-controlled (speed-controlled) to conform to specific ANSI-specifications. The reference for power is: +4 dBu sine wave = 0 VU. Originally designed for broadcast and recording, the slow response of VU's was optimized to match the ear's perception of loudness. VU meters give a good indication of average levels, but should not be relied on to display accurate peak and transient levels (Most modern gear with VU meters includes LED indicators as a supplementary peak display). Most inexpensive pieces of gear do not have true VU meters, rather they have decibel meters.