Pitch-raising up is a technique used to “overcorrect” pianos. For example, a piano that has fallen to A=435Hz needs to be tuned to A=440Hz to achieve the desired A=440Hz. Instead of simply tuning it to 440Hz, it needs to be overcorrected and tuned to 441.57Hz. After some restoring, it will approach 440Hz.

Pianos have 88 notes and over 220 strings. Pitch-raising up takes time; this is what’s commonly referred to as “coarse tuning” and “fine tuning.” Pitch-raising up is like coarse tuning, while the simultaneous tuning and testing are like fine tuning.

New York Piano Tuner ( Chen YN 调音主页)