MATLAB: How to apply highpass, lowpass or bandpass filtering according to the paramaters

digital signal processingsignal processing

I have to apply filtering to a discrete time function.

Input signal is n-by-1 vector. Sampling frequency is also given in Hz. In addition, lower bound and upper bound of the frequency components in Hz that we want to pass through are given. According to these variables I need to decide which type of filtering to apply. How can I understand which one of the lowpass,highpass or bandpass is going to be applied to the input signal.

I appreciate any help, thank you very much…

Best Answer

What are the lower and upper bounds? If the lower bound is 0 and the upper bound is some frequency less than the 1/2 the sampling frequency, that is lowpass, if the lower bound is some frequency greater than 0 and the upper bound is 1/2 the sampling frequency, that is highpass. If the lower and upper bound are greater than 0 and less than 1/2 the sampling frequency, that is bandpass.

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MATLAB: Cut off frequency for butterworth filters

The ‘frequency between 0 and 1’ refers to a normalised frequency with respect to the Nyquist frequency (Nyquist frequency = sampling frequency/2).

For your low-pass filter with a cutoff of 20 Hz and a sampling frequency (Fs) of 2500 Hz, you would define:

Fs  = 2500;
Fco =   20;
Fn  = Fs/2;
Wn  = Fco/Fn;

Since ‘Wn’ is the upper passband frequency, and you will want to use the buttord function to help you design your filter, you will set the stopband frequency at about 1.25 times the passband frequency, and the passband ripple to be 1 dB and the stopband ripple at 10 dB. (These have no relevance to a Butterworth design, but buttord wants them.)

Also, use tf2sos to create the most stable (second-order-section) representation of your filter.

MATLAB: How to design FIR lowpass filter with cutoff frequency, fc1 = 20 Hz and FIR bandpass filter with cutoff frequency fc2 = 10 Hz and fc3 = 35 Hz.

Déjà vu

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

Make the appropriate changes to get the cascaded filter you want.

Best Answer

Related Solutions

MATLAB: Cut off frequency for butterworth filters

MATLAB: How to design FIR lowpass filter with cutoff frequency, fc1 = 20 Hz and FIR bandpass filter with cutoff frequency fc2 = 10 Hz and fc3 = 35 Hz.

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