Chorton
The historical organ pitch standard, usually higher than chamber pitch.
What it means
Chorton (German for “choir pitch”) refers to the pitch standard used by German church organs, mainly in the 17th and 18th centuries. It varied by region but was usually a whole tone to a minor third higher than the chamber pitch (Kammerton) used for secular instrumental music. Before pitch was standardized in the 19th and 20th centuries, singers and instrumentalists had to adapt to different pitches depending on place and occasion.
Musical use
In practice, the mismatch between Chorton and Kammerton meant that vocal and instrumental parts in cantatas were often notated in different keys so that organ, singers, and instruments could sound together correctly. In Bach's cantatas, for example, wind and string parts frequently appear in a different key than the organ part, because the organ played at the higher Chorton.
Chorton should be distinguished from Kammerton, used for secular ensemble music, and from Cornetton, another historical pitch standard. Accurately reconstructing these pitches matters to today's historically informed performers.
Performance practice
If you play Baroque church music on period instruments or at historical pitch, find out beforehand which pitch standard applies to the place and source you are working from; simply transposing by ear can easily lead wind and string players to wrong fingerings.