Desibeli

Desibeli, or decibel, is a logarithmic unit used to express the ratio between two quantities, most commonly sound pressure, acoustic power, or electrical power, as well as amplitudes such as voltage or current. It is widely used in acoustics, audio engineering, and telecommunications because it can express very large ranges of values in a compact form. The decibel is one-tenth of a bel, named after Bell Laboratories and Alexander Graham Bell.

Mathematically, the decibel is defined as dB = 10 log10(P2/P1) for power-like quantities, and dB = 20 log10(V2/V1) (or A2/A1) for field quantities when the same impedance is assumed. The unit is actually a ratio and carries no absolute dimension unless paired with a reference value.

Common reference values include: sound pressure level, with reference P0 = 20 μPa in air; electrical power level, with reference P0 = 1 mW (dBm); and voltage levels, with reference V0 = 1 V (dBV). In digital systems, dB is also used as dBFS (full scale). The dB scale is logarithmic, meaning a small increase corresponds to a multiplicative change in the quantity.

Uses and interpretation: decibels enable comparison of levels across wide dynamic ranges and are central in measuring loudness, transmission loss, signal strength, and device performance. They indicate relative differences rather than absolute quantities.

Notes: Desibeli is the term used in several languages for decibel; accuracy depends on the referenced quantity. Always specify the reference when reporting dB values.