How to design filter using FIR bandpass filter with cutoff frequency 17Hz and 30Hz and IIR lowpass filter with cutoff frequency 25Hz?

design filter by using matlab

Answer 1

[Star Strider]

See my Answer to: how to design IIR highpass filter with cutoff frequency of 20Hz and FIR bandpass filter with cutoff frequency of 10Hz and 15Hz?

It’s essentially the same problem. Change the filter frequencies and sampling frequency as required for your homework assignment.

[SYAZWANI IBRAHIM]

sorry..can you explain more?? because I dont really get where/how did you get Fs, Fn, Wp, Ws and etc..??

[Star Strider]

No apology necessary! This is MATLAB Answers!

Those values are the ones ‘Issac Pang’ provided in his Question. He quoted my code from one of my earlier Answers somewhere, but didn’t include my comment documentation.

Fs: Sampling Frequency (Hz) — Frequency At Which A Continuous Time-Domain Signal Is Sampled By An Analog-To-Digital Converter For Discrete Signal Processing
Ts: Sampling Interval (sec) — Interval Between Consecutive Samples In A Sampled Signal, Ts = 1/Fs
Fn: Nyquist Frequency (Hz) — Highest Uniquely Resolvable Frequency In A Sampled Signal, Also The Frequency Above Which Aliasing Occurs If There Is No Hardware Anti-Aliasing Filter On The ADC
Wp: Passband Frequency For A High-Pass Or Low-Pass Filter, Or (1x2) Frequency Vector For Band-Pass Or Band-Stop Filters
Ws: Stopband Frequency Or Frequencies, Similar To ‘Wp’ With Design Differences
Rp: Passband Ripple (dB) — This Choice Is Based On What You Want Your Filter Passband Characteristic To Be, And Is Irrelevant To Some Filter Designs Such As Butterworth And Chebyshev Type II.  
Rs: Stopband Ripple (dB) — Same Discussion With Different Exceptions; For Example, Both Are Significant In A Cauer Filter

Note that ‘Wp’ and ‘Ws’ values in Hz have to be normalised to (divided by) the Nyquist frequency in Hz in order to use them in the filter design functions, so they are dimensionless.

The stop-band frequency is lower than the pass-band frequency in a high-pass filter, and higher than the pass-band frequency in a low-pass filter. The same logic applies to pass-band and stop-band filters.

This is a very short discussion of a very large topic. If anything is not clear, I will do my best to clarify it.

[SYAZWANI IBRAHIM]

how can the changes in the sampling frequency can affect the highpass or the lowpass filter ? what if the sampling frequency increases, will the filter be lowpass or highpass ?? can you just give me the answer please? haha

[SYAZWANI IBRAHIM]

Design filter using FIR bandpass filter with cutoff frequency, fc1 = 17 Hz and fc2 = 30 Hz and IIR lowpass filter with cutoff frequency fc3 = 25 Hz. What is your designed filter and it cutoff frequency? this is the question given..

[Star Strider]

You have to design your filter using the same sampling frequency as the sampling frequency of your signal. When the sampling frequency changes, you have to re-design your filter. The filter will retain the characteristics of your original design, but the filter coefficients will be different for different sampling frequencies.

You have to be careful that your filter design frequencies are never less than zero and never greater than the Nyquist frequency, or you will not be able to realise your filter.

I covered all of this in my Answer to ‘Isaac Pang’s’ Question on the same topic. This is now quite obviously a homework problem, so having done this much, I leave the rest to you.

[SYAZWANI IBRAHIM]

okay..thank you for your cooperation..i'll try my best to complete this question.. btw, this is not a homework problem..but this is my initiative to understand deeply about this topic by trying to answer this type question..thanks again..have a nice day !

[Star Strider]

My pleasure.

I thought it was homework because it was almost exactly like the previous one that I quoted.

There are three cutoff frequencies: your two pass-band frequencies for your band-pass filter, and your frequency for your high-pass filter. (This would be my answer to it.)

I don’t know the context of the problem you are solving, so I am not certain what the problem wants.

You, too! Have fun!