EGR 224/Active Filter

The following page provides some supplemental information for the Active Filters lab for EGR 224L. It has been updated to Spring, 2020.

Requirements

You will need access to MATLAB with the Signal Processing Toolbox. You can use MATLAB on the Duke system if you connect via VPN; see How To Get Work Done for more on that. Then use a terminal program to connect to Duke. Run the command

xeyes &

to make sure graphics are working. Note that you will not be able to use MATLAB to play the audio this way, but I have uploaded WAV versions of the files so you can still hear the sounds.

You can also use a Virtual Computer from Duke if you do not want to install MATLAB on your own machine. The VCL page has more information on that. One advantage of this is that you can play the audio through MATLAB.

Finally, you can install MATLAB on your own computer. If you installed MATLAB on your own computer but do not have the Signal Processing Toolbox:

• Go to the HOME tab
• Find and click on "Add-Ons"
• Search for Signal Processing
• Click on the link for the Signal Processing Toolbox
• Sign in to install if need be
• Install

Script from 7.4.2

clear
load DukeFightSong
%% Filter constants
R = 10000;   C = 50e-9;

%% Experimental Transfer Function
[EstH, EstF] = tfestimate(SoundIn, SoundOut, [], [], [], samplerate);
EstMag = abs(EstH);
EstOmega = EstF*2*pi;
%% Analytical Transfer Function
s = tf([1 0], [1]);
H = 1 / (1 + s * R * C);
[HMag, HPhase, HOmega] = bode(H, {1, max(EstOmega)});
HMag = squeeze(HMag);
%% Make plot
figure(1); clf
semilogx(EstOmega, 20*log10(EstMag), 'b-')
hold on
semilogx(HOmega, 20*log10(HMag), 'r-')
hold off
xlabel('\omega, rad/s'); ylabel('|H|, dB')
legend('Estimates', 'Theoretical', 'location', 'best')