## Aliasing Distortion

Summary: This module brings out a clear understanding of the aliasing effect when signals are not sampled at the Nyquist Sampling Frequency.

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**Aliasing Distortion**

*A signal composed of components of different frequencies ,when sampled at a sampling frequency less than twice the value of the highest frequency component( the Nyquist sampling frequency)present in the sampled signal, results in the under sampled component posing itself as a low frequency component. This component passes through the system as an alias causing distortion. This is known as aliasing distortion.*

*Illustration of aliasing using Matlab/Simulink:*

```
Simulink Block Diagram:
Total simulation time: 0.05seconds
```

*The Sine wave consists of components of 250Hz,1000Hz,3500Hz*

*This wave is sampled at 4000Hz .The component which is under sampled is 3500Hz.*

*This component passes through posing as a low freq component of 500Hz*

*Simulink model :*

*The Sine Wave block is picked from the Signal Processing Sources Blockset , using the Simulink Library Browser .*

*1.The Sine wave block is given the following block parameter values :*

*Amplitude:[1 4 5]*

*Frequency(Hz): [250 1000 3500]*

*Phase offset(radians):0*

*Sample mode: Discrete*

*Output Complexity :Real*

*Computation method:Trigonometric fcn*

*Sample time:1/4000*

*Samples per frame:1*

*2.The FFT block:*

*Default parameters*

*3.The Spectrum scope block:*

*Buffer Input*

*Buffer size:128*

*Buffer overlap : 64*

*Window type: Hann*

*Window sampling: periodic*

*Specify FFT length:*

*FFT length:128*

*No.of spectral averages:2*

*The Frequency Spectrum indicating 3500Hz signal posing as 500Hz due to aliasing*

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