What is a musical instrument?
My 304-page long answer can be found in my new book Sound Actions: Conceptualizing Musical Instruments that has just been published by the MIT Press:
How do new technologies change how we perform and perceive music? What happens when composers build instruments, performers write code, perceivers become producers, and instruments play themselves? The answers to these pivotal questions entail a meeting point between interactive music technology and embodied music cognition, what author Alexander Refsum Jensenius calls “embodied music technology.” Moving between objective description and subjective narrative of his own musical experiences, Jensenius explores why music makes people move, how the human body can be used in musical interaction, and how new technologies allow for active musical experiences. The development of new music technologies, he demonstrates, has fundamentally changed how music is performed and perceived.