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Wavelets can be used in a range of applications, one of which is noise reduction.
This laboratory shows how to design a model of Wavelet Noise Reduction using Simulink and run it on a Texas Instruments C6000 DSP.
Intermediate. Assumes prior knowledge of MATLAB and Simulink. It also requires a theoretical understanding of wavelets and some knowledge of Texas Instruments DSPs.
This laboratory was originally developed using the following hardware and software:
The Simulink model described here is based on a MATLAB Demo.
Open WaveletDenoising.mdl
Run the model. The colors change to show the different filter channels. Green = high frequency.
The scope output shows how the random noise has been separated out (Residual).
Add an extra scope as shown in Figure 4 to display the Diadic Filter Outputs.
It can be seen that the noise is on Out1, Out2 and Out3. The clean input signal is on Out4.
Double-click on the “Soft Threshold” block. This is the actual noise reduction stage. The fields are in order Out1, Out2, Out3 and Out4.
Here Out1 has been given a threshold of 3. This means that only values>3 are let through.
Out2, Out3 and Out4 have been given the value of 0. This means the whole signal is let through.
The output is shown in Figure 6. Note that the noise associated with Out2 and Out3 have not been reduced.
Double-click on the “Delay Alignment” block. Temporarily remove the delays on Out1 and Out2.
Run the model to see the effect.
From practical experimentation using the Simulink model, you should now understand how wavelet denoising works.
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