This paper presents an experimental study in post-digital luthiery using origami geometries. We explore how our method of fold sensing creates a new class of digital musical instruments through a case study of music and visual composition and performance. We consider how single-fold and multi-fold gestures afford an exploration of sound as a space, where each fold-sensed crease creates a new variable dimension in the musical parameter space, and multi-fold gestures allow multiple parameters to be controlled through origami gestures. We discuss our fabrication method, including material selection, sensor construction, and the selection of origami patterns. The raw sensor data from the instrument are interpreted with our fold-sensing method that can infer four distinct but related types of gestural interaction, including touch, pressure, single-fold sensing, and multi-fold sensing. The data stream conforms to digital music standards, Musical Instrument Digital Interface (MIDI) and Open Sound Control (OSC). We introduce our open-source software toolkit, designed for fostering artistic experimentation, that implements and supports the musical standards. Our case study includes three distinct artistic strategies for interpreting the data stream and discusses the types of gestures employed by each artist in composition and live performance. We conclude that origami gestures show distinctly new types of expressions for both music and visual digital artists.