Re: using the function fir1 and filter

[Joe Koski]

Bryan,

That also confused me the first time I looked at fir1. First, look at http://octave.sourceforge.net/index/index.html for some help, if you haven’t already. 

The variable w is in terms of fractions of  the Nyquist or folding frequency, 1/(2t), where t is the time spacing between the points. For a stop filter it appears that you set w to the edges of the stop band, e. g. [0.3,0.4]. I’ve only used fir1 for low pass, but it should work as a band stop filter or high pass as well.

Keep in mind that IIR filters have better performance (sharper “skirts” etc.), but also can do bad things to the data if you don’t know what you’re doing. 

Joe

on 9/21/04 9:11 PM, Neil Bryan B. Cazar at address@hidden wrote:

how do i specify the center frequency of the bandstop filter using the fir1 funcition? it would only let you specify the range from 0 to 1. how is this related to the frequency? and is the order of the filter related to the number of dB going to be reduced?

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