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I. General description - Frequency graphs |
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fc
, the center frequency, BWp
, the pass-band bandwidth and BWs
, the stop-band bandwidth, determine one of the five possible responses. For the Analog and IIR filters, the cut-off frequency (@Ap
or @Asc
) is given by BWp
, while for the FIRs, ωc
is given by the middle point of the transition width (e.g. (BWp+BWs)/2
for LP).
With these in mind this is how the values of the three frequencies should be: for LP/HP fc=0
, for BP/BS fc>0
, while the ratio between BWp
and BWs
determines whether it's a LP/HP, or a BP/BS. AP is a special case and only the all-pole Analog Active filters (Bessel, Butterworth and Chebyshev) and FIR_FS can achieve it. For that, fc=0
and BWp=BWs>0
.
Satisfying the conditions is not enough, some care should be taken. E.g. if fc=1
, BWp=1k
and BWs=2k
it's a BP case, but the results will probably be unsatisfactory.
©Vlad, 2008 - 2015