Sinusoid with Noise, Frequency domain filtering.

Cuthbert Nyack

Besides using the difference equation 'filtering' can also be done in the frequency domain using the DFT or more realistically the FFT. The applets illustrate 2 possible simple approaches.

For the first case shown below, the spectrum of the signal calculated. The resulting spectrum is used to generate an 'output' by deleting the low amplitude components in the spectrum and finding the inverse transform of what remains. The input is shown in magenta and the output in yellow.
The level below which spectral components are rejected can be changed by changing Lv.

The applet below illustrate a different approach where all frequencies in a certain range are deleted. The bandwidth which is rejected can be changed by changing wr.

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