A sound synthesizer (often abbreviated as "synthesizer" or "synth") is an electronic instrument capable of producing a wide range of sounds. Synthesizers may either imitate other instruments ("imitative synthesis") or generate new timbres. They can be played (controlled) via a variety of different input devices (including keyboards, music sequencers and instrument controllers). Synthesizers generate electric signals (waveforms), and can finally be converted to sound through the loudspeakers or headphones.

Synthesizers use a number of different technologies or programmed algorithms to generate signal, each with their own strengths and weaknesses. Among the most popular waveform synthesis techniques are subtractive synthesis, additive synthesis, wavetable synthesis, frequency modulation synthesis, phase distortion synthesis, physical modeling synthesis and sample-based synthesis. Also other sound synthesis methods including subharmonic synthesis used on mixture trautonium, granular synthesis resulting Soundscape or Cloud, are rarely used. (See #Types of synthesis)