A synthesizer is an electronic musical instrument. A synthesizer has no sound "of its own" - it needs to have speakers or be attached to an amplifier to make audible sounds. Synthesizers are usually equipped with a piano style keyboard. Every key of the keyboard is actually a switch by which the user can switch sound circuits on and off. Keyboards are the most popular input devices, but the user can also choose to use mouthpieces, strings, drum pads or a computer to control the synthesizer. Synthesizers are extremely versatile musical instruments. They can be made to imitate any other instrument - from string-instruments to drums. But the true power of the synthesizer lies in its possibility to create completely new, yet unheard sounds.