How to define cutoff freqeuncy when using rectwin for lowpass filtering?

Hi, when perfoming lowpass filtering, how to choose the cut-off freqeuncy argument? Is it fc/fs/2 or fc/fs? fc is cut off frequency in Hz.

fs %------sampling frequency
fc_normaized = fc/fs/2;--------?
N = 1/fc_normalized;
h = rectwin(N);

ll

fs %------sampling frequency
fc_normaized = fc/fs%-----------------?
N = 1/fc_normalized;
h = rectwin(N);

[Mathieu NOE]

usually we say that a cut off frequency is normalized vs the Nyquist frequency (which is fs/2)

so the right answer is : fc/(fs/2) = 2*fc/fs;

Answer 1

[Sai Pallav]

Hi,

As Mathieu mentioned in the comments cutoff frequency can be calculated using

cutoff = fc/(fs/2);

But rectwin is used for creating a window and it takes argument which specifies the length of the window. Refer rectwin documentation for more info.

Try a similar piece of code for creating a low-pass filter.

% Filter specifications
cutoff_frequency = 1000; % Desired cutoff frequency in Hz
filter_order = 50;
% Calculate window length
window_length = filter_order + 1;
% Generate rectangular window
window = rectwin(window_length);
% Normalize the window
window = window / sum(window);
% Generate ideal low pass filter coefficients
filter_coefficients = fir1(filter_order, cutoff_frequency/(fs/2), 'low');
% Apply the window to the filter coefficients
filtered_coefficients = filter_coefficients .* window;