An electronic tuner is a device used by musicians to detect and display the pitch of notes played on musical instruments. The simplest tuners use LED lights or a needle to indicate approximately whether the pitch of the note played is lower, higher, or approximately equal to the desired pitch. More complex and expensive tuners indicate more precisely the difference between offered note and desired pitch.
Tuners vary in size from units that can fit in a pocket to table-top models or 19" rack-mount units. The more complex and expensive units are used by instrument technicians, piano tuners and luthiers.
The simplest tuners only detect and display the tuning for a single pitch (often "A" or "E") or for a small number of pitches, such as the six pitches used in the standard tuning of a guitar (E,A,D,G,B,E). More complex tuners offer chromatic tuning, which allows all the 12 notes of the scale to be tuned. Some electronic tuners offer additional features, such as adjustable pitch calibration, different tempered scale options, the sounding of a desired pitch through an amplifier and speaker, and adjustable "read-time" settings which affect how long the tuner takes to measure the pitch of the note.
The most accurate tuning devices are strobe tuners, which work in a different way to regular electronic tuners; they are basically stroboscopes. These can be used to tune any instrument, including the initial "beating" of steelpan drums, bagpipes, accordions, calliopes, bells, the pins in Music Boxes or any audio device much more accurately than regular LED, LCD or needle display tuners. However, strobe units are generally much more expensive, and the mechanical elements of a mechanical (rather than electronic-display) strobe require periodic servicing. Therefore, these tuners are mainly used by specialists and professional instrument technicians.