What are the dependent, indepedent, and controlled variables in a Science experiment?

I need to know the variables in a very common experiment. If different volumes of water is vibrated, then different pitches of sound are produced. I've used a crystal glass, water, a pencil, and a tuner. I stuck the glass and listened to the pitch. I changed the volume of water and repeated the process for different pitch of sound. What are my dependent, independent, and controlled variables?