A guitar tuner application on a mobile phone ensures the guitar strings are tuned precisely to the standard audio frequencies for musical notes. Most tuning applications can be used with different types of stringed instruments, helping to rapidly achieve a common tuning among the instruments.
A guitar tuning application allows each string to be independently tuned with precision, avoiding the use of tuning patterns and by-ear matching of string tones. Tuning applications usually default to the use of the standard A4 tuning pitch reference, which is the A note above middle C on a piano. The standard A4 note is 440 Hertz, and other string notes are tuned with precise frequency spacing from the A4 frequency reference. Most tuning applications allow the selection of different pitch references than A4, and alternative tunings may be selected from pre-programmed options, such as drop D or open G tuning.
Many string tuning applications also provide additional functions that benefit the musician. A metronome timing sound is a common feature, often including complex patterns. Chord patterns may be visually displayed on a fret board image, or chords may be identified by entering fretted string positions.
A disadvantage of phone application-based tuners is that when the phone microphone is used rather than an externally connected interface, noise in the environment may disrupt tuning.