In music, an electronic tuner is a device that detects and displays the pitch of musical notes played on a musical instrument. "Pitch" is the perceived fundamental frequency of a musical note, which is typically measured in Hertz. Simple tuners indicate—typically with an analog needle or dial, LEDs, or an LCD screen—whether a pitch is lower, higher, or equal to the desired pitch. Since the early 2010s, software applications can turn a smartphone, tablet, or personal computer into a tuner. More complex and expensive tuners indicate pitch more precisely. Tuners vary in size from units that fit in a pocket to 19" rack-mount units. Instrument technicians and piano tuners typically use more expensive, accurate tuners.
Pocket-sized Korg chromatic LCD tuner, with simulated analog indicator needle
Guitar tuner showing that the "E" string is too sharp and needs to be tuned down
Some rock and pop guitarists and bassists use "stompbox" format electronic tuners that route the electric signal for the instrument through the unit via a 1⁄4-inch patch cable. These pedal-style tuners usually have an output so that the signal can be plugged into an amplifier.
A common LCD clip-on guitar tuner, clipped onto the back of a Fender Telecaster headstock so that the guitarist can tune easily while wearing the guitar. A clip-on tuner attaches to the instrument and senses the vibrations from the instrument, even in a noisy environment.
Piano tuning is the act of adjusting the tension of the strings of an acoustic piano so that the musical intervals between strings are in tune. The meaning of the term 'in tune', in the context of piano tuning, is not simply a particular fixed set of pitches. Fine piano tuning requires an assessment of the vibration interaction among notes, which is different for every piano, thus in practice requiring slightly different pitches from any theoretical standard. Pianos are usually tuned to a modified version of the system called equal temperament.
A man tuning an upright piano
A piano tuner's most basic tools include the tuning lever (or "hammer") and mutes
An A440 tuning fork
Some common piano tuning tools: From top to bottom: a tuning lever, a felt mute, a rubber mute, a felt temperament strip (left), and a Papps mute.