Feldton
Historical name for E-flat major as the basic key of military brass (trumpets, horns).
What it means
Feldton (German for “field key”) is an older name for the key of E-flat major, which was regarded as the basic tuning of military brass. The name goes back to Feldmusik, the outdoor music of military and hunting bands, for which trumpets and horns were preferably built and tuned in this pitch.
Musical use
The term belongs to the history of brass instruments and wind band music: where signal and march music was to sound outdoors, a tuning was chosen for the brass in which the natural harmonics yielded comfortable, carrying notes. This practice explains why E-flat major occurs especially often in military marches and wind music of the Classical and Romantic periods.
The Feldton should be distinguished from E-flat major in the general musical sense, which as a key also serves strings and keyboard instruments; “Feldton” denotes only the historical role tied to wind practice. The term is uncommon today and turns up mainly in older textbooks.
Performance practice
If you play in a wind band that cultivates many pieces in E-flat major or related flat keys, use this historical link as an aid to intonation: the harmonics of instruments pitched in E-flat and B-flat lie especially favorably there. Nevertheless, check tuning together in the ensemble regularly.