MATLAB: What is actually Normalized Frequency

# glossaryMATLAB

I mean how could we define or describes it? I am new to MATLAB. I have calculated the the Frequency of 1st zero, Level of 1st slobe, Level of 2nd slobe and level of 3rd slobe in Rectangular, Triangular, Hann, Hamming, Blackman etc type in Frequency Domain after typing "wintool" in the window command of the MATLAB. Thanks

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Normalised frequency is frequency in Hz (or more generically cycles/second or some other unit) divided by the sample frequency of your signal in Hz (or the same units as your original frequency).

So a normalised frequency of 1 represents your sampling frequency and 0.5 represents the Nyquist frequency.

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Yes, that's correct there will be frequency components at [-750 -250 250 750] so the bandwidth is 1500 Hz, you have to sample at least at 1500 Hz.

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If you have a 50 Hz sampling frequency, the Nyquist frequency — in this instance the normalising frequency if you are designing a digital filter — is 25 Hz. So if you want a 15 Hz cutoff for a lowpass filter for instance, the normalised frequency, ‘Wn’ would be:

Fs = 50;                    % Sampling Frequency (Hz)
Fn = Fs/2;                  % Nyquist Frequency (Hz)
Fc = 15;                    % Cutoff Frequency (Hz)
Wn = Fc/Fn;                 % Normalised Cutoff Frequency (Dimensionless)

So Wn = 15/25 = 0.6

EDIT — For fft scaling, the best documentation is in the R2015a fft version. See specifically the code between the first two plot images.

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