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).