| 摘要 |
PROBLEM TO BE SOLVED: To provide a cutoff frequency variable digital filter capable of modifying simply filter characteristics in correspondence to a change of a specified cutoff frequency when digital-recorded speech information is reproduced at a variable speed. SOLUTION: A cutoff frequency variable digital filter is constituted by a dead zone avoid limiter 41, a geometric convergence interpolation calculation unit 42, a filter coefficient generator 43, an infinite length impulse response lowpass digital filter (IIR digital filter) 44, a delay element 45, and an angular frequency transfer function memory 46 of the infinite length impulse response (IIR) filter. The dead zone avoidance limiter 41 compares value 2F-limit which changes the result if rounding off after multiplication with cutoff frequency coefficient 2F-n(n-1) of a last sample but one, and when the cutoff frequency coefficient 2F-n(n-1) is smaller than 2F-limit, the cutoff frequency coefficient 2F-n(n-1) is replaced by the value of 2F-limit. Thus, in a geometric convergence interpolation calculation of the cutoff frequency coefficient, it is possible to avoid nonconverge of the cutoff frequency coefficient. |
