Digital filters

I am trying to build a band pass filter from .1 to 40 Hz, IIR or FIR, and then analyze it in matlab. Does anyone know reasonable parameters for this kind of filter (Fs=256). I am having trouble building one that has nice properties.

Thanks Kim

[Jan]

What is "nice" enough for your purpose?

[Kim]

Thank you for your answer. I have been away. And have found the answer.

Answer 1

[Rick Rosson]

Hi Kim,

Do you have access to the Signal Processing Toolbox in MATLAB? If so, you can use the fdatool to design the filter very easily.

For more information:

doc fdatool

HTH.

Rick

[Kim]

Thank you for taking time to answer this. I was away for a bit so didn't get it.

Answer 2

[Gaurav Gupta]

Use fir1 for designing filter and freqz for viewing its frequency response

[Kim]

Thank you for your answer.

Answer 3

[Daniel Shub]

Introductory DSP textbooks tend to provide formula for calculating parameters for some simple IIR filters (e.g., Butterworth). The signal processing toolbox in MATLAB provides the butter command. A first order Butterworth filter can be obtained with:

[b, a] = butter(1, [.1, 40]./128)

The parameters are: b =

    0.3477         0   -0.3477

a =

    1.0000   -1.3030    0.3047

[Walter Roberson]

Question: Is the "128" there the Nyquist frequency, Fs/2 ?

[Daniel Shub]

Yes, Kim said Fs=256.

[Kim]

Thank you for this answer. I ended up using a butterworth designed in fdatool but then moved it to an mfile.