A quick primer on “inharmonicity”.
On the surface piano tuning may seem like a fairly straight forward, yet tedious and time consuming process – start at the A following middle C, tune it to a pitch of 440 Hz, and go from there in either direction at perfect 2:1 octave intervals (equal-temperament tuning) until you’re done. With an electronic tuner, this shouldn’t be that hard, right?
The truth is that it’s not at all that simple. While one may think that a string tuned to a specific note at the proper frequency/pitch is perfectly in tune, other factors are at play, not the least of which is the human ear and perception, which can throw things off balance. What we generally consider to be a distinct pitch actually contains a series of subtle nuances called overtones. These overtones can cause an otherwise technically perfectly tuned piano to be perceived as being sharp in pitch, due to the inconsistencies in tone produced along the length of a piano’s string. The phenomenon is known as inharmonicity, and is generally more prevalent in the bass and high treble registers. Other factors, such as a string’s composition and thickness, as well as the presence of dirt and rust can also result in slight rises in frequency.
This is where a piano tuner’s experience and training truly come into play. To account for and eliminate inharmonicity, a tuner will “stretch” tune a piano in increments slightly further apart than the standard 2:1 ratio so that the piano will audibly be perceived as in-tune by the listener. This is a skill and practice that takes years to hone and perfect. So remember, while that discount piano tuner you found online might seem like a good deal at first, chances are he or she are not ready (or qualified) to put in the work truly necessary to do the job right. Be sure to always hire a qualified and experienced piano tuner and technician. Your ears (and in the long run – your wallet) will thank you for it.