How to eliminate aliasing? (Antialiasing filter):

• Aliasing can be completely eliminated by taking the following actions:

• Use a bandlimiting low pass filter and pass the signal x (t) through it before sampling as shown in fig.

• This filter has a cut-off frequency at $f_C$ =W, therefore it will strictly bandlimit the signal x (t) before sampling takes place. This filter is also called as Antialiasing filter or prealias filter.

• Increase the sampling frequency $f_S$ to a great extend i.e. $f_S$>>>2W. Due to this, even though x (t) is not strictly bandlimited, the spectrums will not overlap. A guard band is created between the adjacent spectrums as shown in fig.

• Thus aliasing can be prevented by,

1. Using an Antialiasing or prealiasing filter and

2. Using the sampling frequency $f_S$>2W.