This program performs directional wave separation in a Discrete-Time Acoustic Pulse Reflectometry (APR) system, based on Louis et al.'s method (1993). The algorithm requires recordings from two microphones (pm1c and pm2c) positioned at axial intervals within the source tube. The microphone spacing (shift) represents the time samples needed for sound waves to travel between the two microphones. The outputs, pm2plus and pm2minus, represent forward and backward propagating waves at microphone 2 within the source tube.
Key Reference: Louis, B.; Glass, G.; Kresen, B.; Fredberg, J. \"Airway Area by Acoustic Reflection: The Dual Microphone Technique,\" Journal of Biomechanical Engineering, 1993, 115, 278.