Real world ultrasonic signals and their application in teaching signal processing

In our never-ending quest to find ways to interest and motivate our students, we have recently found something new for our "bag of teaching tricks." Ultrasonic signals present a unique andragogical opportunity in any course where signal processing theory and techniques are taught. The authors have recorded (or obtained) a number of naturally occurring ultrasonic signals (e.g., bat echolocation sounds and dolphin whistles) as well as artificially generated ultrasonic signals (e.g., output from a dog whistle and signals from a device from ThinkGeek called an Annoy-a-tron). This paper discusses how these signals can be effectively used to teach, demonstrate, and reinforce the concepts of time dilation/compression, frequency translation, spectral analysis/estimation, and aliasing.