What happens when you tune a piano? There are four steps in tuning.
1. Pitch 2. Temperment 3. Octaves 4. Unisons
1. Pitch: The tuner must have with him a source of pitch, such as a tuning fork or electronic device that can supply verification of the correct pitch. I use an old fashioned tuning fork that vibrates at 440 vibrations per second, producing the A above middle C. I match one piano string from that A to the fork. This is an international pitch standard that all pianos are designed for.
2. Temperment: Starting with the A-440 string, I create the precise harmonic relationships necessary within all twelve pitches of the scale. A good temperment will give you perfectly even, rich harmonies in every possible major and minor chord combination and in every possible key. It is called temperment because it requires all the intervals between these notes to be 'bent' or tempered ever so slightly, so that all combinations come out evenly.
3. Octaves: When the temperment is perfected, then I extend that harmonic foundation all the up and all the way down the piano by matching all the A's, all the A sharps, all the B's, etc., using octaves. To be honest, octaves are also 'tempered' or bent ever so slightly, too, in order to get the richest possible harmonies. This octave bending, often called 'stretching', can vary from one piano to the next, depending on the piano's design.
4. Unisons: The term unison means all the strings played by a single hammer. In the lowest bass there is only one string per each hammer. A little higher up each hammer strikes two strings. And one or two octaves higher, each hammer is striking three strings. When a hammer strikes two, or three strings, those strings must be so closely pitched so that they sound like one string singing, perfectly matched.
But tuning is more than just setting these pitches, it also means that you handle all the parts of the singing mechanism so that they stay in tune as long as possible. There are many minute stresses within the piano string and tuning pins that must be considered.
