A rotational recording apparatus that comprises a shock sensor and that adaptively
processes the output of the shock sensor to obtain a feed forward signal, so as
to implement a stable operation within a practical range. In a rotational recording
apparatus wherein a VCM system having a transfer function (G) and a controller
having a transfer function (H) perform feedback, the band of a signal(s) of a shock
sensor (S) is limited by a bandpass filter (F), and a resultant signal (f) is employed
to obtain the output of an adaptive filter (FIR). A signal (p) that a phase shift
filter (P) outputs by shifting the phase of the signal f is employed as a signal
to be transmitted to a parameter adaptation algorithm (PAA). Within the limited
band, the phase of the phase shift filter P matches the phase of G/(1+GH) within
a range of 90 degrees.