Abstract
This paper describes a system of automatic piano tuning. Fig. 1 show the block diagram of the system. The standard frequency generator (4) generates signals of the frequency equal to 100 multiples of the standard piano frequency. Deviation detector (5) counts the number of the signals in the gate time of 10 periods of the fundamental of the piano tone. When the number is 1000, it is considered that the frequency of the piano tone is exactly equal to the standard piano frequency. Deviation detector generates positive direct current when the number is smaller than 1000, and negative direct current when the number is larger than 1000. The servomotor (7) is controlled with the direct current, and the tuning pin is turned slowly until the frequency of the piano tone almost agrees to the standard piano frequency. Fig. 3 shows the principle of the deviation detector, and Fig. 4 is the photograph of the automatic tuning device for piano.
