A sound synthesizer (often abbreviated as "synthesizer" or "synth", also spelled "synthesiser") is an electronic musical instrument that generates electric signals converted to sound through loudspeakers or headphones. Synthesizers may either imitate other instruments or generate new timbres. They are often played with a keyboard, but they can be controlled via a variety of other input devices, including music sequencers, instrument controllers, fingerboards, guitar synthesizers, wind controllers, and electronic drums. Synthesizers without built-in controllers are often called sound modules, and are controlled via MIDI or CV/Gate.