Acoustic noise cancellation  (Page 2/3)

Experiment with different values of delay to see how it effects the operation of the LMS Filter.

Changing the number of weights

Double-click on the “LMS Block” and change the Filter Size (number of Weights).

If the number of Weights is large, the algorithm will be slow to run.

If the number of Weights is too small, the filter will not remove the noise properly.

Summary

From practical experience, you should now know how to use LMS algorithm and how you can adjust the Step size (mu), the filter delay and the number of weights to obtain optimum performance.

You will now apply this to building a real-time model.

Real-time model

You have now run the simulation and understand the operation of the LMS Filter.

You will now implement the Real-Time Acoustic Noise Cancellation Model using the Texas Instrument C6713.

Texas instruments dsk6713 setup

Alternatively, you can use computer loudspeakers.

Starting up code composer studio

Connecting the dsk6713

Start Code Composer Studio for DSK6713 and use Debug ->Connect

Opening an existing model

Start MATLAB 7.3.0 R2006b:

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

Highlight “Embedded Target for TI C6000 DSP” then “Audio”. Click on “Wavelet Denoising”. We are going to use this as our template.

Viewing the original model

The “Wavelet Denoising” model is now displayed.

Saving the model

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

Changing the title

Delete the “Info” box. Change the title to “LMS Noise Reduction”. You may also wish to move the “DSK6713” icon to the left hand side.

The original wavelet noise reduction algorithm

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

Delete blocks

Delete the blocks and connect the input directly to the output. Add a title.

Overview of the lms model

We are going to implement the model shown below.

We will now update the empty model by dragging-and-dropping some library components onto the model.

Changing the input to microphone

Double-click on the blue box to the left marked “DSK6713 ADC”. The following screen will appear.

Change the “ADC source” to “Mic In”.

If you have a quiet microphone, select “+20dB Mic gain boost”.

Set the “Sampling rate (Hz)” to “48 kHz”.

Set the “Samples per frame” to 64.

When done, click on “OK”.

Important: Make sure the “Stereo” box is empty.

The dac settings

The DAC settings need to match those of the ADC. Check that it uses the same sampling rates. Click on “OK”.

Adding an lms block

The Simulink block for LMS is to be found in the “Signal Processing Toolbox”.