What is a Pitch Raise?
According to the Piano Technicians Guild, (PTG.org)
The piano’s main acoustical structure, the soundboard, is made of wood, which reacts constantly to climate changes. High humidity causes the soundboard to swell, stretching the piano strings to a higher pitch, while lower humidity can flatten the soundboard, lowering tension on the strings and causing the pitch to drop. This could mean that you need to try the process of pitch raising to restore your piano to the proper tone of A440.
A pitch raise, a pitch correction, a pre-tuning, or a double/triple tuning is simply a process designed not for accuracy but rather to reset the piano back to an overall pitch of A440.
We as Technicians must raise the tension of over 200 strings, which puts a lot of strain on the piano’s structure and increases pressure on the soundboard, bridges, and plate. Each of these strings holds approximately 150-200 lbs. of tension, a combined total of approx. 20 tons.
It’s impossible to make such a big jump in pitch and have a “stable tuning” in one pass. So, what we have to do is first raise all the strings to their proper average tension levels. i.e. A440. After a pitch raise a “Normal or Regular” tunings allow us to stabilize and phase all the strings and tuning pins to be accurately tuned. Generally, a piano that is tuned and serviced regularly does not need to receive this procedure, however:
Vast changes in temperature, or humidity causes loose tuning pins. Also, heavy playing and the placement of your piano in a room can cause pitch to change, in drastic measure.
Each year that passes by… your piano’s pitch drops further and further away from its proper tension levels. Tuners must work very carefully to stretch the piano’s wires to calculated points of tension. immediately (as intended), to its intended point of bearing – before the actual tuning takes place. Also note: a new piano at the factory receives new strings, several tunings, and several months pass before the piano is released to the public for sale.