Stuart Hyatt returns with another sonic marvel in the Field Works series, taking the listener into truly uncharted acoustic territory. *Ultrasonic* is perhaps the first album ever to use bat echolocations as compositional material. For Stuart Hyatt, the world is a recording studio where people, places, and things become the instruments. Working under the name Field Works, Hyatt has assembled a remarkable group of artists to create new music from his samples and soundscapes. For this volume, Hyatt has brought together an extraordinary group of contributors: Eluvium, Christina Vantzou, Sarah Davachi, Ben Lukas Boysen, Machinefabriek, Mary Lattimore, Felicia Atkinson, Noveller, Chihei Hatakeyama, John Also Bennett, Kelly Moran, Taylor Deupree, Jefre Cantu-Ledesma, Julien Marchal, and Player Piano. *Ultrasonic* is part of a larger project on the endangered Indiana bat. Generously funded by the IUPUI Arts & Humanities Institute and the National Geographic Society, each album contains an official printed booklet of The Endangered Species Act of 1973.