A first series of filter coefficients stored in a memory itself
corresponds to a given filter characteristic such as a given high cutoff
frequency. A second series of filter coefficients is generated by
performing an interpolation process on the first series of filter
coefficients. At that time, the contents, such as interpolation
coefficients, of the interpolation process are varied in correspondence
to a desired filter characteristic to be achieved, so that the
interpolation process generates a second series of filter coefficients
according to an impulse response characteristic that is obtained as a
consequence of expanding or compressing, in a time-axis direction, an
impulse response characteristic represented by the given first series of
the filter coefficients. Thus, by the interpolation process, there is
produced such a second series of filter coefficients that achieves a
different filter characteristic (e.g., different high cutoff frequency).
Where the sampling frequency of a time series of digital signals is to be
changed from a given first frequency to a second frequency, an aliasing
noise frequency may vary depending on a value of the first or second
sampling frequency, in which case it is necessary to vary the cutoff
frequency of a filter for eliminating the aliasing noise. However, by
performing the interpolation process in the above-noted manner, the
filter characteristic for eliminating the aliasing noise can be varied as
desired.