FFT and aliasing

1. How does aliasing affect FFT?
2. What is aliasing in Fourier transform?
3. What is aliasing of frequency spectrum?
4. How can aliasing be avoided?

How does aliasing affect FFT?

Recognizing Aliasing in the FFT

It is common to have acquired signals with a fundamental frequency less than half the sample rate, but the harmonics of that signal may be greater than half the sample rate and they will alias. This shows up in the FFT as frequencies that fold back into the display.

What is aliasing in Fourier transform?

Aliasing is the effect of new frequencies appearing in the sampled signal after reconstruction, that were not present in the original signal. It is caused by too low sample rate for sampling a particular signal or too high frequencies present in the signal for a particular sample rate.

What is aliasing of frequency spectrum?

Those high frequencies fold back onto the spectrum of the discrete time series and appear as lower frequencies. The phenomenon that is caused by undersampling the continuous signal is termed frequency aliasing.

How can aliasing be avoided?

The solution to prevent aliasing is to band limit the input signals—limiting all input signal components below one half of the analog to digital converter's (ADC's) sampling frequency. Band limiting is accomplished by using analog low-pass filters that are called anti-aliasing filters.