butterworthIIRFilter(order, type, freq, sampfreq)

import signals.filters.iir-1

Design Butterworth digital IIR filter.

orderThe order of the filter.
typeThe type of the filter ("lowpass", "highpass", "bandpass", "bandstop"). See description.
freqCorner frequency/frequencies. See description.
sampfreqIf given, the sample frequency of the signal. If not, an analog filter will be designed.
return valueTransfer function object.

Parameter type is a string value describing the filter type:

The meaning of parameter freq depends on the type of the filter. If it is a bandpass or bandstop filter, then it is an array of frequencies, otherwise it is a single frequency.

For more information, see http://en.wikipedia.org/wiki/Butterworth_filter.

import signals.filters.iir-1;
Design a digital Butterworth filter
filt=butterworthIIRFilter(4, "", 100Hz[100Hz,200Hz], 600Hz)
import signals.filters.iir-1;
Design an analog Butterworth filter
filt=butterworthIIRFilter(4, "", 100Hz[100Hz,200Hz])
import signals.filters.iir-1;
Plot filter characteristics