dezibels

Deizibels (dezibels) refers to the decibel, a logarithmic unit used to express ratios between two quantities, most often power or amplitude. It is a relative unit, meaning a value in dB indicates how much one quantity differs from a chosen reference. The term comes from the bel, a unit proposed by Bell, with one decibel equal to one tenth of a bel. In English, the standard spelling is decibel, while dezibel is used in some languages and contexts.

Formulas and interpretation

For power ratios, the decibel is defined as dB = 10 log10(P2/P1). For voltage or current ratios with the same impedance, dB = 20 log10(V2/V1). Because the scale is logarithmic, a small change in dB can represent a large or small physical change depending on whether one is discussing power or amplitude. As a rule of thumb, a 10 dB increase typically corresponds to about a tenfold increase in power, while a 20 dB increase corresponds to a tenfold increase in amplitude (with constant impedance).

References and common scales

In acoustics, sound levels are often expressed as dB SPL, where the reference is 20 micropascals in air. 0 dB SPL is roughly the threshold of human hearing; everyday levels range from 30–60 dB in quiet to 100–120 dB in loud environments. In electronics, related scales such as dBm (power relative to 1 milliwatt), dBV (voltage relative to 1 volt), and dBu (a voltage reference used in audio) are widely used.

Measurement considerations

Decibels are used across electronics, telecommunications, and acoustics due to their ability to represent large dynamic ranges compactly. Weighting curves (for example, A-weighting) are often applied to account for human hearing sensitivity when measuring sound levels.