Schmelzer is specialised in vocal repertoire and performance practices which he studied primarily over the course of long research stays in Italy, Spain, Portugal and Morocco. He studied several medieval vocal traditions in depth, their continuation and survival in later times, ornamentation styles, and the logic of operative knowledge. Combined with insights from anthropology, history, human geography and ethnomusicology, this has resulted in various publications and concert programmes.
Schmelzer gives lectures and has published several essays and articles. He is currently writing a book about vocal practices, derived from 10 years of expertise with graindelavoix. In 2011, Schmelzer became the first ‘Creative Fellow in Musicology’, a collaboration between the Utrecht Early Music Festival and the Centre for Humanities at Utrecht University.