Pitch Correction
WHAT IS A PITCH CORRECTION?
A pitch correction, sometimes called a pitch raise or rough tuning, is a process of adding back lost tension to the entire piano. Your piano has over 200 strings, and each of those strings holds about 150-200 pounds of tension. That adds up to around 20 TONS of tension applying pressure to the soundboard, bridges, and plate. Over time, whether the piano is played or not, tension is lost if the piano is not tuned regularly or if it endures significant uncontrolled humidity swings; and it must be added back before the piano can hold a fine tuning.
Piano strings can begin to stretch immediately and drop in pitch after this tension is added back. The pitch raise procedure is designed to add enough tension back to the strings so that when they begin to stretch, they end up near to their intended pitch. Because we are dealing with such a significant amount of tension, the soundboard, the frame, and even the cast iron plate flexes somewhat during this process. This flexing, though invisible to the human eye, has such an effect that if we were to try to fine tune the piano at standard pitch when it's not properly tensioned, it would be back out of tune by the time we finish the job. Once the instrument is stabilized near proper tension, a fine tuning can be completed.
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WHEN IS A PITCH CORRECTION NECESSARY?
A piano loses approximately 4-5% of its tension annually whether it is played or not. (100% is equal to a half step or any two adjacent notes on the piano). This is primarily due to seasonal changes in humidity. If a piano is between 5-25% flat, a quick pitch raise/correction necessary and can be done immediately prior to the fine tuning (during the same appointment). If a piano is more than 25% off from standard pitch, it may require a second tuning appointment approximately 1 month later before it will hold a stable fine tuning.
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HOW CAN I AVOID THIS IN THE FUTURE?
Various factors can contribute to the need for a pitch correction, but there are two things you can do specifically to help avoid future pitch corrections - 1) humidity control, and 2) a standard fine tuning every 6 months. Whether you play your piano much or only a little, standard tunings every 6 months ensure that proper tension is maintained. Regularly scheduled tunings increase the life of the instrument and can help to avoid the pitch correction process entirely. As for humidity control, the best way to accomplish stable humidity for a piano is install the Dampp-Chaser "Piano Life Saver" humidity control system. More info about that system can be found at https://stryketuning.com/piano-life-saver