As a music theorist, Theisen specializes in the analysis and pedagogy of 20th-century and contemporary classical music. He has presented research at academic conferences on the music of Elliott Carter, Gyorgy Ligeti, Pierre Boulez, and Frank Martin. He is currently writing a book on the late music of Tristan Keuris.

Read: PhD dissertation (Music Theory, Florida State Univ., 2010) A Multifaceted Approach to Analyzing Form in Elliott Carter's Boston Concerto

Read: review of Brian Alegant's book The Twelve-Tone Music of Luigi Dallapiccola in Music Theory Online 19.1

Read: a brief analytical essay on Elliott Carter's song "Una Colomba"

Read: What's the Big Deal about All-Interval Tetrachords and the All-Triad Hexachord?

Read: Text, Harmony, and Transformation in Frank Martin's Sechs Monologe aus Jedermann

Theisen has served as engraver of the 8th, 9th, and (forthcoming) 10th Editions of the best-selling textbook Music for Sight Singing by Nancy Rogers and Robert Ottman. 

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