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LABORATORY EXERCISE 3: MATLAB M IXER ANDS IMPLE S IGNAL MEASUREMENT

For this lab exercise a mixer script is included in the files given to you. This mixer

will come in handy as your knowledge in DSP advances as you can add signalprocessing at different points of the script.

Aim

To write and understand a simple mixer using Matlab.

To assess the addition of sine waves, noise bands, and delayed noise bands.

Activities using the Mixer script

Run the mixer program, understanding each section of the code. This is a goodexample of a script where you could use break points or divide the script into cells.Files are included in the zip file but feel free to use any files of your choice. Just

remember that it will make more sense if you think of them as separate audio

streams to be mixed.

Change pan parameters. How do the pan parameters relate to the output and toeach other?

Add a bus routine to your script. A bus in a typical mixer console is a split of achannel that is routed to an additional channel (or bus) that will typically be sub

mixed with other signals before the final mixer output. Typical applications include

applying effects to groups of channels. Make sure your bus has also a gain control.

Add a delay to your mixer. The delay should include a gain parameter. Simulate asituation where a signal is presented with one reflection, arriving a few

milliseconds later at a lower level. Generate random noise and put it through the

delay, listen to the effect this has on the sound of final output.

Activities on signal measurement

Take the RMS level of a sine wave. In order to do this import or create a sine waveand call it wave, then use this code:

squaredWave = wave .^2;

meanSquared = mean(squaredWave);

rmsLevel = 10 * log10(meanSquared);

Take two copies of this sine wave and add them together, what effect does thishave on the RMS level?

Do the same with two identical white noise bands. What is the difference? Do the same with two different (randomly generated) white noise bands. Using two identical noise bands, offset one in time (say 10ms) from the other, and

add them together. What effect does this have on the sound produced?

Try this using a sine wave, what is the effect with the copy delayed by half thewavelength?

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Digital Audio Systems DESC9115 15/03/11

Include a measurement output in your mixer.

To hand in next week:

Simple mix (no delay) with level and panning (in audio format). Mix using delay (with noise or instrument signals). All results (as numbers) from the measurement section. Include type of signal and

measurement.