If x(t) is not band limited or fs is than 2w, then aliasing or foldover occurs

If we use a reconstruction filter with pass band extending from –fs/2 to + fs/2 then its o/p will not be an undistorted version of original signal x(t)

Distortion occurs due to overlapping of adjacent spectrum

It appears as a fold over inside the desired spectrum.

Aliasing: This phenomenon of high frequency. in the spectrum of the original signal (+) taking on the identity of lower frequency in the spectrum of the sampled signal Xs(t) is called as aliasing or fold over error.