[2.6.1] Tuning the Piano to the Tuning Fork
One of the most difficult steps in the tuning process is tuning the piano to the tuning fork. This difficulty arises from two causes. (1) the tuning fork has a different (usually shorter) sustain than the piano so that the fork dies off before you can make an accurate comparison. (2) the fork puts out a pure sine wave, without the loud harmonics of the piano strings. Therefore, you cannot use beats with higher harmonics to increase the accuracy of the tuning as you can with two piano strings. One advantage of electronic tuners is that they can be programmed to provide square wave reference tones that contain large numbers of high harmonics. These high harmonics (they are needed to create those sharp corners of square waves) are useful for increasing the tuning accuracy. We must therefore solve these two problems in order to tune the piano accurately to the tuning fork.
Both difficulties can be solved if we can use the piano as the tuning fork and make this transfer from fork to piano using some high piano harmonic. To accomplish such a transfer, find any note within the muted notes that makes loud beats with the fork. If you can't find any, use the note a half tone down or up; for example, for tuning fork A, use Ab or A# on the piano. If these beat frequencies are a bit too high, try these same notes an octave lower. Now tune the A on the piano so it makes the same frequency beats with these reference notes (Ab, A#, or any other note you had picked). The best way to hear the tuning fork is to press it against your ear lobe, as described above, section 3, or to press it against any large, hard, flat surface.