Band Pass Equiripple FIR Filter.

Cuthbert Nyack
In this applet a band pass equiripple filter for small number of extrema can be derived. In this case Fp1(56), Fp2(57) are the lower and upper cut off frequencies of the filter. Ft(58) is the width of the transition region, Te(59) is the total number of extrema, Pe(61) is the number of the extrema in the pass band, S1e(60) is the number of extrema in the lower stop band between 0 and Fp1(56) - Ft(58) and the number of extrema in the upper stop band is Te(59) - Pe(61) - S1e(60). In this applet changes should be made slowly.



The image below shows the filter obtained with the applet's starting parameters, pass band from 0.2 to 0.3, stop bands 0 to 0.12 and 0.38 to 0.5. The width of the transition region is 0.08. There are 8 extrema in each stop band and 7 in the pass band. The stop band attenuation is 71dB.
Below the width of the transition is reduced from 0.08 to 0.04. There are 16 extrema in each stop band and 11 in the pass band. The stop band attenuation is 71dB.
The filter below has 103 taps, a transition bandwidth of 0.04 and a stop band attenuation of 82dB.

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COPYRIGHT 2008 Cuthbert Nyack.