Volume unit

(engineering acoustics) A unit for expressing the audio-frequency power level of a complex electric wave, such as that corresponding to speech or music; the power level in volume units is equal to the number of decibels above a reference level of 1 milliwatt as measured with a standard volume indicator. Abbreviated VU.

A unit used to measure the strength of electrical waves produced by microphones. In sound recording, broadcasting, and public address systems, microphones convert acoustical signals into electrical waves that are nonperiodic and cannot be simply described in terms of voltage, current, power, or frequency. To provide a practical means of assigning a numerical value to the strength of such waves, the concept of “volume” is used. The volume of an audio program wave is the magnitude of the wave as measured with a standard volume indicator. This is a meter calibrated to read in volume units (vu, pronounced vee-you).

telecommunications. Symbol vu. USA 1938 A measure of the magnitude of complex signals, such as analogue representations of speech and music, which, even for pure notes, have a multitude of different frequencies, each with its own amplitude at any moment. It is quantitatively defined as the number of decibels relative to a standard signal that is normally taken as a sinusoidal wave developing 1 milliwatt of power against an impedance of 600 ohms.
[Chinn H. A., Gannett D. K., Morris R. M. Proc. Inst. Radio Engrs Vol. 28, 1 (1940) Acoustical Terminology Vol. 1, 405 American Standards Assoc. Z 24.1 (1951)]