Open WaveletDenoising.mdl

Figure 1: Opening WaveletDenoising.mdl

Run the model. The colors change to show the different filter channels. Green = high frequency.

Figure 2: Wavelet Model Showing Color Coding

The scope output shows how the random noise has been separated out (Residual).

Figure 3: Scope Output

Add an extra scope as shown in Figure 4 to display the Diadic Filter Outputs.

Figure 4: Monitoring the Dyadic Filter Outputs

It can be seen that the noise is on Out1, Out2 and Out3. The clean input signal is on Out4.

Figure 5: Noise Levels at Dyadic Filter Outputs

Double-click on the “Soft Threshold” block. This is the actual noise reduction stage. The fields are in order Out1, Out2, Out3 and Out4.

Figure 6: Noise Levels at Dyadic Filter Outputs

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.

Figure 7: Threshold only applied to Out1

Double-click on the “Delay Alignment” block. Temporarily remove the delays on Out1 and Out2.

Figure 8: Removing the Delay Alignments

Run the model to see the effect.

From practical experimentation using the Simulink model, you should now understand how wavelet denoising works.

Start Code Composer Studio for C6713 DSK and use Debug -> Connect.

Figure 10: Startup Screen for Code Composer Studio (CCS)

Start MATLAB 7.3.0 R2006b:

Figure 11: Opening an Existing Demo

Click on “Demos”. The following screen will appear:

Figure 12: Selecting the Audio Demo Models

Highlight “Embedded Target for TI C6000 DSP” then “Audio”. Click on “Wavelet Denoising”.

The “Wavelet Denoising” model is now displayed. Double-click on the “function()” box.

Figure 13: Wavelet Denoising Parent

The “Wavelet Noise Reduction Algorithm” model is now displayed.

Figure 14: Wavelet Denoising Algorithm

For convenience, copy the model to the MATLAB “Work” directory where most models are stored.

Figure 15: Copying the Model to the MATLAB “Work” directory

In order to run the model on the C6713 DSK and be able to compare the performance with and without noise reduction, we will make some small modifications to the demo model.

Figure 16: The Modified Algorithm

You will now update the existing model by dragging-and-dropping some library components onto the model.

Double-click on the blue box to the left marked “C6713 DSK ADC”. The following options will appear.

Figure 17: Setting up the ADC for Microphone Input

Change the “ADC source” to “Mic In” and tick the “Stereo” box. If you have a quiet microphone, tick the “+20dB Mic gain boost” box. When done, click on “OK”.

The DAC settings need to match those of the ADC. Check that they are the same.

Figure 18: Setting the DAC Parameters

To change between no wavelet denoising and with wavelet noise reduction, we will use a DIP switch of the C6713 DSK.

Figure 19: Adding a Switch and LED

Select View -> Library Browser -> Embedded Target for TI C6000 DSP. Highlight “C6713 DSK Board Support”.

Drag-and-drop the “Switch” block onto the model. Also drag-and-drop the “LED” block onto the model.

The DIP switch needs to be configured. Double-click on the “Switch” block.

Put at tick in all of the boxes and set “Data type” to Integer. The “Sample time” should also be set to “–1”.

Figure 20: Setting up the DIP Switch Value

We now need to setup a way to switch between straight through without noise reduction and with wavelet noise reduction.

Select View -> Library Browser -> Simulink. Highlight “Commonly Used Blocks”.

Drag-and-drop a “Constant” onto the model.

Drag-and-drop a “Switch” block onto the model.

Drag-and-drop a “Relational Operator” block onto the model.

Figure 21: Selecting the Commonly Used Blocks

The switch values lie between 0 and 15. We will use switch values 0 and 1. Double-click on the “Constant” block. Set the “Constant value” to 1 and the “Sample time” to “inf”.

Figure 22: Setting the Echo Delay Gain

Click on the “Signal Data Types” tab. Set the “Output data type mode” to “int16”. This is compatible with the DAC on the C6713 DSK. Click on “OK”.

Figure 23: Data Type Conversion to 16-bit Integer

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

Figure 24: Changing the Relational Operator

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

Figure 25: Changing the Output Data Type

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

Figure 26: Joining the Blocks

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”.

Figure 27: Checking the Dyadic Analysis Filter Bank

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

Figure 28: Checking the Delay Alignment

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

Figure 29: Checking the Thresholds

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

Figure 30: Checking the Dyadic Synthesis Filter Bank

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

Figure 31: Returning to the Parent System

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

Figure 32: Building the Model

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

Figure 33: The Completed Model Running under Code Composer Studio

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

Figure 34: Switch Position 0

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

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

Figure 35: Switch Position 1 for Wavelet Noise Reduction

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

Figure 36: Dyadic Analysis Filter Bank set to Symlets

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”.

Figure 37: Configuring the Dyadic Synthesis Filter Bank

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

Figure 38: Building the Model

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