Theater auf der Wieden
By 1787 he had joined the theatrical company of Emanuel Schikaneder, for which he sang the demanding role of Osmin in Mozart's opera "The Abduction from the Seraglio" and other roles. In 1789 the troupe settled at the Theater auf der Wieden in Vienna. Gerl participated in a system of joint composition used by Schikaneder's troupe, in which "Singspiele" were produced rapidly by having several composers collaborate. As such, Gerl may have been the composer of the aria "Ein Weib ist das herrlichste Ding", for which Mozart wrote a set of variations for piano, K. 613 (the composer may instead have been another singer-composer in the troupe, Benedikt Schack).