Regular tuning is at the heart of maintaining your piano. Tunings need to occur to compensate for changes in temperature, humidity, and vibration of strings from playing.
A rule of thumb is that tunings should be done often enough to hold pitch at A440.
The minimum requirement is at least one tuning a year although depending upon your situation and the condition of your piano this could mean up two or more tunings per year, with minor repairs and adjustments being carried out at the time of tuning and on the principal that a minor repair now negates bigger problems later on.
While manufacturers' recommendations vary on the number of yearly tunings they generally agree that a piano should be tuned at least two times a year.
What is a pitch raise? What is A440?
As time and other factors act on a piano the tension on the strings tends to drop until the pitch is very low. If a tuner brings the strings to the correct frequency in one pass, he or she will find that no matter how carefully they try to do it, the increasing tension created by the tuning process will change the strings they first tuned, often significantly.
THERFORE: If a piano is too far out of tune, it will not stay in tune after one “tune.” It will require a preliminary “rough” tuning first, known as a pitch raise. The internationally established correct frequency for the note “A” above middle “C”, is A440 and is the starting pitch from which the rest of the piano is tuned, theoretically, a piano can be in tune with itself even if "A" is far from the "correct" frequency.
It is important to understand.
Tuning defines the relationship of one note to another, whereas “pitch“ describes the specific frequency at which the piano is tuned.
When we tune a piano, we start by making sure that this "A" is exactly at that frequency, and then the rest of the piano can be tuned by establishing the correct relationships that result from that starting pitch.
Therefore it is possible to get a piano which is so far from correct pitch that it won’t stay in tune in one "go or pass." It has been found that one or two quick tunings to get all the notes “close" to their proper relationships between each other followed by a careful tuning can achieve the required result. This process of performing one or two "rough" tunings before the "real" tuning is called a pitch raise. It obviously takes more time, and most tuners charge extra for this.
Pianos that have not been tuned in two years or more usually require this extra work, but new instruments where the strings are still stretching can require this process as well. Sometimes age and the pianos condition have deteriorated so far as to make retuning the piano to concert pitch impossible. This is a discussion that needs to be held between the tuner and the customer as a experienced tuner can fairly quickly determine if a piano can be “A” tuned or “B” tuned to any sort of standard that would be acceptable to both the customer and the tuner.