Abstract: A method and an apparatus for adjusting the vibration frequency of vibrating objects such as piano strings, by stepwise adjustment of the vibration frequency of a vibrating object. The amount of the required adjusting operation in each of the adjustment steps is calculated by the equation:.DELTA..theta..sub.i = K.sub.i (f.sub.s - f.sub.pi-1)wherein:i represents an integer such as 1, 2, 3, ...;.DELTA..theta..sub.i represents the amount of adjustment in the i-th adjusting step;f.sub.pi -1 represents the vibration frequency after the (i-1)th adjusting step;K.sub.i represents the constant employed in the calculation of the i-th adjusting step;The constant (K.sub.1) for the initial (i=1) adjusting step is predetermined; andThe constant K.sub.i (i=2, 3, ...) for the second and subsequent adjusting steps is calculated by the equation: ##EQU1## WHEREIN: .DELTA..theta..sub.I-1 REPRESENTS THE AMOUNT OF ADJUSTMENT IN THE (I-1)TH ADJUSTING STEP;f.sub.

Abstract: A system for measuring the vibration frequency of a vibrating object useful for the adjustment of the vibration frequency of a piano string or like vibrating objects. In this system, the vibration of the vibrating object is converted to an electric signal, based on which signal is sought the difference between the vibration frequencies of any two adjacent harmonics of the vibrating object, i.e. the fundamental vibration frequency of the vibrating object is sought. The electric signal is led to a counter via a voltage-controlled variable band-pass filter. The middle frequency of the pass-band of this filter is controlled by a sweeper and varies continuously. For each agreement of this middle frequency of the pass-band with any one of the harmonics, the output of the filter presents a peak. The frequency corresponding to each peak is detected by a counter. The fundamental frequency is calculated from the difference between the frequencies corresponding to any adjacent peaks of the outputs of the filter.