Improved design of long FIR filters using the frequency masking technique

Frequency specifications imposing small transitions between pass-bands and stop bands lead to FIR filters having long impulse responses and highly correlated coefficients. Multirate techniques can reduce the resulting redundancy and the combination of a sharp undersampled filter with a couple of interpolating filters can lead to significant gains in arithmetic complexity. The alternative implementation proposed, and the corresponding filter design can bring an additional gain in the total operation count.