Tuning requires each of the piano’s approximately 200 strings to be adjusted to the proper tension to achieve a pleasant musical sound. Pianos are usually tuned so that the A above middle C, is at a pitch of 440 Hz. This results in the piano being in tune with other musical instruments and recordings.
Pitch Correction and Tuning:
If the piano has not been tuned for several years or has been subjected to extreme humidity changes, it may require a pitch correction in addition to a tuning. The longer a piano has been neglected, the more it is out of tune. Typically, the pitch of a neglected piano is much lower than it should be. The goal of pitch correction is to get the entire piano within about 5% of the desired final pitch. Tuning can then be performed by making only very small adjustments in string tension. Without the pitch correction, tuning would require very large changes in string tension. This would result in flexing of the piano frame. As each string is adjusted, the frame flexes, and all previously tuned strings become slightly out of tune. The end result is a piano that is still not in tune.
Pitch correction must be performed so that change in string tension does not result in one section of the piano being at a grossly different tension than another section of the piano. If not done properly, the piano could possibly be damaged during the procedure. Because tuning and pitch correction takes longer than tuning alone, the cost is higher. It cannot be determined if a pitch correction is needed until the time of service.