The ultrasonic applied to sound refers to anything above the frequencies of audible sound, and nominally includes anything over 20,000Hz. Frequencies used for medical diagnostic ultrasound scans extend to 10MHz and beyond. Sounds in the range 20-100kHz are commonly used for communication and navigation by bats, dolphins, and some other species. Much higher frequencies, in the range 1-20MHz, are used for medical ultrasound. Such sounds are produced by ultrasonic transducers. A wide variety of medical diagnostic applications use both the echo time and the Doppler shift of the reflected sounds to measure the distance to internal organs and structures and the speed of movement of those structures.