Units of level

The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a power ratio of 101/10 (approximately ) or root-power ratio of 101/20 (approximately ).

In music, an octave (: eighth) or perfect octave (sometimes called the diapason) is an interval between two notes, one having twice the frequency of vibration of the other. For instance, the interval between C4 and C5 (in scientific pitch notation) is an octave. { \override Score.TimeSignature 'stencil = ##f \relative c' { \time 4/4 \set Score.tempoHideNote = ##t \tempo 1 = 20 1 } }

In Western music theory, a semitone (also called a half step or half tone) is one of two parts into which a whole tone is divided. Semitones appear as the smallest steps in chromatic scales (which divide the octave into twelve semitones), arising on keyboards between the pitches of two adjacent keys. For example, C is adjacent to D; the interval between them is a semitone. Semitones are among the most dissonant intervals when sounded harmonically.

thumb|John Napier after whom the unit is named

musical interval unit

logarithmic unit expressing the ratio of a physical quantity

musical interval

unit of logarithmic frequency interval, corresponding to a ratio of 10 between the frequencies

unit of information; log₂(10) bits

unit of evolutionary change

thumb|1/100 heptaméride (jot), 1/10 heptaméride (decameride), 1 heptamérides, 10 heptamérides, 100 heptamérides, 1,000 heptamérides (decade).