Das Wohltemperierte Clavier I, Fuga X

Description

Just two lines make up this E minor fugue, No. 10 of Book I and the only two-voice fugue in either book of The Well-Tempered Clavier. While the other fugues use three to five voices, this one builds a whole fugue from a pair. Book I itself, with its autograph title page of 1722, is a cycle of preludes and fugues through all the major and minor keys.

It is a two-voice fugue in E minor and 3/4. The subject is a line of fine notes that never pauses, and the two voices chase each other at speed. There is a passage where both hands play the same line in octaves, a known rarity in contrapuntal writing. At 63 seconds it is the shortest of the fugues here, yet with 811 notes its density is very high; the range runs from E2 to C6 and fits on a 61-key keyboard.

It is rated advanced. With only two voices, every uneven note and every rhythmic slip is heard directly. The main challenge is to match the quality of sound between the hands in fast motion. Lower the playback speed a long way, check in the score view which hand has the subject, and compare the two lines with the hand colours. Repeat the octave passage with an A-B loop and raise the speed bit by bit until the hands line up exactly.

Bach's collection of preludes and fugues for keyboard, covering all 24 keys and regarded as the summit of contrapuntal writing.