The Clavier-Übung III, sometimes referred to as the German Organ Mass, is a collection of compositions for organ by Johann Sebastian Bach, started in 1735–36 and published in 1739.
It is considered Bach's most significant and extensive work for organ, containing some of his musically most complex and technically most demanding compositions for that instrument.
In its use of modal forms, motet-style and canons, it looks back to the religious music of masters of the stile antico, such as Frescobaldi, Palestrina, Lotti and Caldara. At the same time, Bach was forward-looking, incorporating and distilling modern baroque musical forms, such as the French-style chorale.
The work has the form of an Organ Mass: between its opening and closing movements—the prelude and "St Anne" fugue in E-flat, BWV 552—are 21 chorale preludes, BWV 669–689, setting parts of the Lutheran mass and catechisms, followed by four duets, BWV 802–805. The chorale preludes range from compositions for single keyboard to a six-part fugal prelude with two parts in the pedal.
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The Praeludium's main theme is played on a Hauptwerk 8' Plenum coupled to the RP 8' Plenum for clarity.
The UW has 8, 4, 2, and 1' stops.
The echo themes are played on the RW with echo's on the UW.
The other manual interludes played on the RP.
The pedal in on Prestant 16' Plenum basis with Fagot 16' added // No coupler.
In the big HW / Ped theme I subtracted the Fagot.
Last main theme with coup[ler HW/Ped and Posaune 16