Although his lowly circumstances precluded a university education, the prince - and his successors - encouraged his musical training and sent him to different German cities.
In 1792, he was appointed Kapellmeister (effectively director of music) by von Schwarzburg-Rudolstadt; this post was formerly held by his tutor, Scheinpflug.
Although these are not included in contemporary lists of works, Koch uses the exposition of the first movement of one of these symphonies without author specification as a sheet music example (from his book Versuch einer Anleitung zur Komposition [Attempt at a Guide to Composition], third and last part, p. 386), which could be taken as an indication of his authorship.
However, he became best known for his published works on musical theory and his Musiklexikon [Music Dictionary] (1802), which was the most influential since that of Johann Gottfried Walther (1732) and prior to the encyclopedias of Gustav Schilling (1835–38) and Hermann Mendel & August Reissmann (1870–83); it summarised the body of knowledge of the Baroque period and early Classical period.
Versuch einer Anleitung zur Komposition was the first book to deal with the systematic and detailed structure of harmony, melody and musical syntax, making it the most important forerunner of Hugo Riemann's alternative theories.