Editing Piano (section)

=== Tuning ===
{{Further|Piano key frequencies}}[[File:Piano tuner.jpg|thumb|left|A [[piano tuning|piano tuner]]]]Pianos are heavy and powerful, yet delicate instruments. Over the years, professional piano movers have developed special techniques for transporting both grands and uprights, which prevent damage to the case and to the piano's mechanical elements. Pianos need regular tuning to keep them on correct pitch. The hammers of pianos are voiced to compensate for gradual hardening of the felt, and other parts also need periodic regulation. Pianos need regular maintenance to ensure the felt hammers and key mechanisms are functioning properly. Aged and worn pianos can be rebuilt or reconditioned by piano rebuilders. Strings eventually must be replaced. Often, by replacing a great number of their parts and adjusting them, old instruments can perform as well as new pianos.

[[Piano tuning]] involves adjusting the tensions of the piano's strings with a specialized wrench, thereby aligning the intervals among their tones so that the instrument is [[Musical tuning|in tune]]. While guitar and violin players tune their own instruments, pianists usually hire a piano tuner, a specialized technician, to tune their pianos. The piano tuner uses special tools. The meaning of the term ''in tune'' in the context of piano tuning is not simply a particular fixed set of [[Pitch (music)|pitches]]. Fine piano tuning carefully assesses the interaction among all notes of the chromatic scale, different for every piano, and thus requires slightly different pitches from any theoretical standard. Pianos are usually tuned to a modified version of the system called [[equal temperament]]. In all systems of tuning, each pitch is derived from its relationship to a chosen fixed pitch, usually the internationally recognized standard concert pitch of A<sub>4</sub> (the A above [[middle C]]). The term [[A440 (pitch standard)|A440]] refers to a widely accepted frequency of this pitch: 440&nbsp;Hz.

The relationship between two pitches, called an [[Interval (music)|interval]], is the ratio of their absolute frequencies. Two different intervals are perceived as the same when the pairs of pitches involved share the same frequency ratio. The easiest intervals to identify, and the easiest intervals to tune, are those that are [[Just intonation|just]], meaning they have a simple whole-number ratio. The term ''[[Musical temperament|temperament]]'' refers to a tuning system that tempers the [[Just intonation|just intervals]] (usually the perfect fifth, which has the ratio 3:2) to satisfy another mathematical property; in equal temperament, a fifth is tempered by narrowing it slightly, achieved by flattening its upper pitch slightly, or raising its lower pitch slightly. A temperament system is also known as a set of "bearings". Tempering an interval causes it to [[Beat (acoustics)|beat]], which is a fluctuation in perceived sound intensity due to interference between close (but unequal) pitches. The rate of beating is equal to the frequency differences of any harmonics that are present for both pitches and that coincide or nearly coincide. Piano tuners have to use their ear to "[[Stretched tuning|stretch]]" the tuning of a piano to make it sound in tune. This involves tuning the highest-pitched strings slightly higher and the lowest-pitched strings slightly lower than what a mathematical frequency table (in which octaves are derived by doubling the frequency) would suggest.