2.7 Wavelet denoising  (Page 3/3)

Setting the relational operator type

Double click on the “Relational Operator” block. Change the “Relational operator” to “==”. Click on the “Signal Data Types” tab.

Setting the relational operator data type

Set the “Output data type mode” to “Boolean”.

Joining the blocks

Move the blocks and join them as shown in the Figure below.

Checking the dyadic analysis filter bank

Double click on the “Dyadic Analysis Filter Bank” block. The values of the Dyadic Analysis Filter Bank are shown below. You do not need to change them yet. Click on “OK”.

Checking the delay alignment

The delay alignment is shown below, with different delay times for the different frequencies.

Checking the soft threshold

The “Soft Threshold” sets the threshold below which noise is ignored for each of the four channels. Zero means no noise reduction.

Checking the dyadic synthesis

Double-click on the “Dyadic Synthesis Filter Bank”. There is no need to change the values at this time. Click on “OK” when done.

Returning to the parent system

From the Toolbar, select the “Up Arrow” icon. This returns you to the next higher level.

Building the model

Selecting real-time workshop

Select Tools ->Real-Time Workshop ->Build Model.

The completed model running on code composer studio

From the folders on the left, select the source code for the project.

Different settings on the c6713 dsk

Microphone straight through to loudspeakers

To check out the microphone and loudspeakers, set the DIP switches on the C6713 DSK as follows:

The microphone is fed directly to the loudspeakers. There is no noise reduction.

Switch position for wavelet noise reduction

To run the “Wavelet Noise Reduction” subsystem, set the DIP switch to 1.

Modifying the model

The next stage is to modify the model. We will change the wavelet type to “Symlets”.

Changing the filter type

Double-click on the “Dyadic Analysis Filter Bank” block. Change the “Filter” field to “Symlets”. Click on “OK”.

Updating the dyadic synthesis filter bank

The wavelet type should be the same as that used in the Dyadic Analysis Filter Bank. Double-click on the “Dyadic Synthesis Filter Bank” block. Change the “Filter” field to “Symlets”. Click on “OK”.

Building the model

Select Tools ->Real-Time Workshop ->Build Model.

Running the updated model

Run the updated model and listen to the effect of using different filter types.

Some things to try

You may wish to experiment with different settings. Here are some suggestions.

Change the wavelet types

Inside the “Dyadic Analysis Filter Bank” are different wavelet types. Which are suitable for wavelet denoising and which are not? Note: you will also have to alter the values used in the “Dyadic Synthesis Filter Bank”.

Change the delay alignment times

Experiment with the delay alignment times. Try higher and lower values.

What is the effect of completely removing the “Delay Alignment” block?

Change the noise reduction thresholds

In the “Soft Threshold” block, change the values. The existing vector of [3, 2, 1, 0] reduces high frequency noise, but does not affect low frequencies.

Create your own subsystem

Add your own subsystem block controlled by the DIP switches and add your own wavelet denoising algorithm. Choose your own wavelet, number of channels, sampling frequency and thresholds.