Tibetan singing bowls are similar to humming crystal glasses. A mallet is used to vibrate the metal bowl by sliding along the edge in a circular motion. This creates a standing wave. The bowl acts as a resonating chamber, each edges' wave reflects off of the opposite side; which gives it it's unique sound. If the person controlling the vibrations does it gently enough and at the correct speed, the frequency remains constant while the amplitude will most likely increase. An increase in the speed of these pulses can create an increase in frequency and vise-versa. A difference in the medium, such as having a different size or kind of metal, can also affect the pitch of its hum. This is how Tibetan singing bowls work.