Quartercomma

Quartercomma, often written as quarter-comma meantone, is a family of musical tuning systems in which the perfect fifth is tuned narrower than a just 3:2 fifth by one quarter of the syntonic comma. The syntonic comma, about 21.5 cents, is the small discrepancy between certain closely related just intervals. By dividing this comma into four equal parts and subtracting one part from each fifth, the fifths become roughly 696 to 697 cents instead of the pure 702 cents. This adjustment brings the major third, around 386.3 cents (the 5:4 interval), much closer to just intonation, at the expense of other intervals and a lack of uniformity across the scale.

Historically, quarter-comma meantone emerged from Renaissance theory as a compromise that improves the consonance of thirds on keyboard instruments. It gained prominence in the 16th to 18th centuries as a practical tuning for ensembles and music that favored a limited set of keys. Because the fifths are not evenly tempered, the tuning yields keys with varying degrees of intonation quality, and some keys or spellings can sound notably out of tune, limiting modulatory flexibility compared with later well temperaments or equal temperament.

In modern practice, quarter-comma meantone is primarily of historical and scholarly interest. It is studied in the context of early music performance, historical instrument construction, and some microtonal or software-based recreations of period tunings. Related topics include the syntonic comma, just intonation, and other meantone and well-temperament systems.