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 to indicate approximately whether the pitch of the note is lower, higher, or 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, clip on an instrument, sit on a table-top, all the way up to rack-mounted units. The more complex and expensive tuners are generally used by instrument technicians, piano tuners and luthiers.
The simplest tuners can only detect the tuning for a single pitch, 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 and the sounding of a desired pitch through an amplifier and speaker.
Considered one of the most accurate tuning devices, strobe tuners work in a different way to regular electronic tuners; they are basically stroboscopes. These can be used to tune an instrument 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.
Most tuners contain a microphone and/or an input jack (for electric instruments such as electric guitar), circuitry for detecting the pitch, and some type of display (an analog needle, an LCD simulated image of a needle, LED lights, etc). Some tuners, such as pedal tuners, have an output so the tuner can be connected in-line from an electric instrument to an amplifier or mixing console. While small tuners are usually battery powered, some tuners also have a jack for an optional AC power supply.