temperament

In music, a system of tuning (‘tempering’) whereby the intervals of the scale are made slightly larger or smaller than the ‘natural’ scale of acoustical theory, to allow for key changes in a piece of music. According to acoustical theory, notes such as D♯ and E♭ are slightly different in pitch. In equal temperament, the octave is divided into 12 equal semitones, so that pairs of notes like D♯ and E♭ are adjusted to the same pitch so that the ear ignores the difference and regards it as one or the other depending on context. This is the standard modern tuning for the piano. Due to the difference being spread across all 12 notes in the octave, one can play in any key with an equal amount of compromise in the tuning. This is especially useful when playing music that modulates from one key to another.

Johann Sebastian Bach composed The Well-Tempered Clavier, a sequence of 48 preludes and fugues in every key of the chromatic scale (to be played without any retuning between each one), to demonstrate the versatility of tempered tuning.

Many choirs that sing early music without instrumental accompaniment use ‘just intonation’, a non-tempered scale where ‘real’ thirds (D-F♯ not D-F♯/G♭) are used, which, once heard, makes equal temperament sound less clean when heard immediately after. This is possible because Renaissance music does not modulate very suddenly or widely and because adjustments can be made during performance where necessary, due to the flexibility of the voice.