can someone please explain me the x-axis in the attached figure?

About the normalized frequency. I mean what does it represent. Please guide me in detail

Answer 1

[Star Strider]

In discrete (uniformly-sampled) signals, the highest usable frequency is the Nyquist frequency, defined as half the sampling frequency. All frequencies in the Fourier transform of a sampled signal are therefore ‘normalised’ from zero to the Nyquist frequency, expressed in ‘pi radians/sample’. You can get the x-axis of your figure in Hz if you multiply it by the Nyquist frequency.