Decimation filter

A decimation filter for accepting first data at a first sampling frequency and outputting second data at a second sampling frequency, for removing folding noises from an output signal produced from said second data and having an output signal bandwidth, comprising:

• input data storing means for storing said first data standardized at said first sampling frequency are input;
• filter coefficient storing means in which a predetermined number of filter coefficients are stored in association with each of a series of the first data in the predetermined number;
• calculation means for generating said second data by calculation using the first data and the filter coefficients associated with the first data to output said second data at said second sampling frequency, wherein said second sampling frequency is equal to said first sampling frequency divided by an integer n;
• and
• said filter coefficients providing a filter output characteristic such that cutoff frequency bands, having a bandwidth at least equal to said output signal bandwidth and disposed on upper and lower sides of frequencies that are integer multiples of the second sampling frequency, have a minimum attenuation level greater than a minimum attenuation level of outer frequency bands on upper and lower sides of said cutoff frequency bands and extending therebetween.