Coupling the Heart to Musical Machines

Biofeedback is being used more recently as a general control paradigm for human-computer interfaces (HCIs). While biofeedback especially from breath has seen increasing uptake as a controller for novel musical interfaces, new interfaces for musical expression (NIMEs), the community has not given as much attention to the heart. The heart is just as intimate a part of music as breath and it is argued that the heart determines our perception of time and so indirectly our perception of music. Inspired by this I demonstrate a photoplethysmogram (PPG)-based NIME controller using heart rate as a 1D control parameter to transform the qualities of sounds in real-time over a Bluetooth wireless HCI. I apply time scaling to "warp" audio buffers inbound to the sound card, and play these transformed audio buffers back to the listener wearing the PPG sensor, creating a hypothetical perceptual biofeedback loop: changes in sound change heart rate to change PPG measurements to change sound. I discuss how a sound-heart-PPG biofeedback loop possibly affords greater control and/or variety of movements with a 1D controller, how controlling the space and/or time scale of sound playback with biofeedback makes for possibilities in performance ambience, and I briefly discuss generative latent spaces as a possible way to extend a 1D PPG control space.