The theremin works without the slightest touch. It's got two antennae -- one horizontal and one vertical -- each of which has an electromagnetic field surrounding it. When you move your hand in front of the instrument, you create interference. If you've ever tried to improve a fuzzy picture on an analog television with rabbit-ear antennae, you've created a similar effect to the principle behind the theremin [source: Levenson]. Our hands and bodies contain a natural capacitance (stored electric charge) that affects electromagnetic fields.
When your hands alter the theremin's surrounding electromagnetic fields, the interference causes an audible sound. The electromagnetic field around the horizontal antenna controls the volume of that sound, and the vertical one controls the pitch.
For the purposes of our hypothetical example, pretend you're a right-handed thereminist, with the horizontal antenna on your left and the vertical on your right. (Left-handed thereminists can have a special version made with the setup reversed, or they can simply turn the instrument around and approach it from the opposite side.) Using your right hand, you can change pitch by moving it at shoulder-height back and forth between your body and the antenna. The closer your hand gets to the antenna, the higher the pitch. Pulling your hand away lowers the pitch -- the lowest pitch occurs about 2 feet (0.6 meters) away from the antenna.
Of course, while you're playing the theremin, you've got to control the volume in conjunction with the pitch. To do this, move your hand up and down (not back and forth, like you do to control the pitch) over the horizontal antenna. The lowest volume starts as you hold your hand about an inch (2.5 centimeters) above the horizontal antenna. As you lift your hand up, the volume gets louder. As your hand rises about a foot (0.3 meters) from the antenna, you'll achieve the loudest volume.
We should note that these spans are approximate because volume and pitch depend on the individual instrument. This also means that the distance between the individual notes can vary. In some machines, you'll experience a delayed response between your hand movement over the horizontal antenna and the change in volume. Each player becomes familiar with his or her own instrument to know exactly how wide these spans are.
Obviously, playing a song with this quirky instrument takes coordination and practice. Next, we'll get some tips from the experts.