decibel [dB]

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(n.) 1. In acoustics, a unit used to measure the amplitude of sound. 2. In audio engineering, a unit that expresses the difference in intensity between two signals. The dB system provides information about the ratio of two powers. If the ratio between the power of two signals is two to one, there is a difference of 3 decibels between them. In 1939, the electronics industry adopted a standard value for 0 dB—a 1-milliwatt reference signal at 1000 Hz in a 600-ohm line. This .001-watt reference, known as dBm, represents a level of 0.7746 volts.