A Pitch Raise is a kind of ‘pre-tuning’ that will bring the pitch of a piano up further than it needs to be, in order to allow it to fall back within the correct range for a subsequent fine tune.
If a piano is more than 5 cents off of desired pitch (the distance from one piano key to the next is “100 cents”), the string's metal “memory” will cause it to move back toward it's original pitch very soon. This will result in a piano sounding “out of tune” again.
To minimize the number of times one must tune the piano, a measured over pull pre-tuning will get it to fall back closer to the desired pitch. This is called a Pitch Raise.
If a piano is more than 20 cents off before this Pitch Raise-Tune, it will also need another tuning in about 6 months because the strings are stretching and finding their equilibrium again.
If a piano is more than 50 cents out, this second tuning will most likely need to be done sooner than 6 months. After that next tuning, the piano’s tune should be stable for its usual schedule of tuning.
The metal wires, referred to as "strings", will be adjusting to their new tension and will need to become flexible again at the new nodes of vibration at that pitch. This is one reason that keeping a piano in tune helps it sound sweeter.
A Pitch Raise can be done on a piano and then a fine tune in the same service call. I typically schedule a 2-hour time slot for a Pitch Raise/Tune.
On some very old pianos with brittle strings, an “over pull” will be more than it can handle without a string breaking. On these, we recommend a special series of tunings. We will discuss these as the need arises.