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hw6/feedback/Ryan_HW6_ECE210.m

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+%%%% ECE-210-B HW6 - Filters - James Ryan
+% James Ryan, 03/27/24
+
+% preamble
+close all; clc; clear;
+
+%% Generate white noise
+Fs = 44100; % Hz = s^-1
+N = Fs*2; % 2s * 44100 samples/sec = 88200 samples of noise
+F = linspace(-Fs/2, Fs/2, N); % range of noise
+
+% noise generation
+% good way
+noise = randn(1, N); % intensity of noise
+
+% funny way - requires `fortune` as a dependency
+%noise = fortune_favors_the_fontaine(Fs, 2); 
+
+% thank you!
+		% you're welcome!
+shifted_fft_mag = @(sig, len) fftshift(abs(fft(sig, len))) / len;
+
+
+%% Butterworth Filter
+		% had to change `5` to `end`, but otherwise perfect.
+Hbutter = butterworth;
+fvm_butter = fvtool(Hbutter, 'magnitude');
+axm_butter = fvm_butter.Children(end);
+axm_butter.YLim = [-60 5];
+axm_butter.Title.String = 'Butterworth Bandpass Filter Magnitude Plot';
+
+fvp_butter = fvtool(Hbutter, 'phase');
+axp_butter = fvp_butter.Children(end);
+axp_butter.Title.String = 'Butterworth Bandpass Filter Phase Plot';
+
+butter_noise = Hbutter.filter(noise);
+
+fftm_butter = shifted_fft_mag(butter_noise, N);
+
+figure;
+plot(F, fftm_butter);
+xlim([-Fs/2 Fs/2]);
+xlabel("Frequency (Hz)");
+ylabel("Magnitude (dB)");
+title("FFT of noisy signal passed through Butterworth Bandpass Filter");
+
+% to save you, i played it back in the matlab terminal:
+%soundsc(noise)
+%soundsc(fftm_butter)
+% to me, its just a mostly mute audio track minus two bursts of sound.
+% that must be the negative and positive passband regions
+% so the filter took the noise, and just took the regions outside of
+% the band and killed them.
+
+%% Elliptic Filter
+Hellip = elliptic;
+fvm_ellip = fvtool(Hellip, 'magnitude');
+axm_ellip = fvm_ellip.Children(end);
+axm_ellip.YLim = [-60 5];
+axm_ellip.Title.String = 'Elliptical Bandstop Filter Magnitude Plot';
+
+fvp_ellip = fvtool(Hellip, 'phase');
+axp_ellip = fvp_ellip.Children(end);
+axp_ellip.Title.String = 'Elliptical Bandstop Filter Phase Plot';
+
+ellip_noise = Hellip.filter(noise);
+
+fftm_ellip = shifted_fft_mag(ellip_noise, N);
+
+figure;
+plot(F, fftm_ellip);
+xlim([-Fs/2 Fs/2]);
+xlabel("Frequency (Hz)");
+ylabel("Magnitude (dB)");
+title("FFT of noisy signal passed through Elliptical Bandstop Filter");
+
+%soundsc(fftm_ellip)
+% I can hear this one.. come back? like very faintly
+% I guess it goes to show how butterworth doesnt have that elliptic
+% stopband portion, and everything decays to -inf dB. Interesting
+% difference!
+% same pattern as the past passband
+
+%% Chebyshev Type 1 Filter
+Hcheb1 = chebyshev1;
+fvm_cheb1 = fvtool(Hcheb1, 'magnitude');
+axm_cheb1 = fvm_cheb1.Children(end);
+axm_cheb1.YLim = [-60 5];
+axm_cheb1.Title.String = 'Chebyshev Type I Lowpass Filter Magnitude Plot';
+
+fvp_cheb1 = fvtool(Hcheb1, 'phase');
+axp_cheb1 = fvp_cheb1.Children(end);
+axp_cheb1.Title.String = 'Chebyshev Type I Lowpass Filter Phase Plot';
+
+cheb1_noise = Hcheb1.filter(noise);
+
+fftm_cheb1 = shifted_fft_mag(cheb1_noise, N);
+
+figure;
+plot(F, fftm_cheb1);
+xlim([-Fs/2 Fs/2]);
+xlabel("Frequency (Hz)");
+ylabel("Magnitude (dB)");
+title("FFT of noisy signal passed through Chebyshev I Lowpass Filter");
+
+%soundsc(fftm_cheb1)
+% It sounds choppy, almost, where it wibbles in and out for the starting portion 
+% where its present. Definitely not the choice for audio filters!
+% Unless you `want` that distortion in like music production, in which case, go for it
+% Sort of sounds like a car engine firing
+
+%% Chebyshev Type 2 Filter
+Hcheb2 = chebyshev2;
+fvm_cheb2 = fvtool(Hcheb2, 'magnitude');
+axm_cheb2 = fvm_cheb2.Children(end);
+axm_cheb2.YLim = [-60 5];
+axm_cheb2.Title.String = 'Chebyshev Type I Highpass Filter Magnitude Plot';
+
+fvp_cheb2 = fvtool(Hcheb2, 'phase');
+axp_cheb2 = fvp_cheb2.Children(end);
+axp_cheb2.Title.String = 'Chebyshev Type II Highpass Filter Phase Plot';
+
+cheb2_noise = Hcheb2.filter(noise);
+
+fftm_cheb2 = shifted_fft_mag(cheb2_noise, N);
+
+figure;
+plot(F, fftm_cheb2);
+xlim([-Fs/2 Fs/2]);
+xlabel("Frequency (Hz)");
+ylabel("Magnitude (dB)");
+title("FFT of noisy signal passed through Chebyshev II Highpass Filter");
+
+%soundsc(fftm_cheb2)
+% Its passband is sorta similar to the butterworth passband, but its die-out
+% has an audible drop off to me. maybe i missed that in others with elliptic
+% stop bands? No just played back fftm_ellip, and that dropped immediately. hmm
+% placebo, perhaps

hw6/feedback/butterworth.m

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+function Hd = butterworth
+%BUTTERWORTH Returns a discrete-time filter object.
+
+% MATLAB Code
+% Generated by MATLAB(R) 23.2 and Signal Processing Toolbox 23.2.
+% Generated on: 27-Mar-2024 18:56:52
+
+% Butterworth Bandpass filter designed using FDESIGN.BANDPASS.
+
+% All frequency values are in Hz.
+Fs = 44100;  % Sampling Frequency
+
+Fstop1 = 6300;        % First Stopband Frequency
+Fpass1 = 7350;        % First Passband Frequency
+Fpass2 = 14700;       % Second Passband Frequency
+Fstop2 = 17640;       % Second Stopband Frequency
+Astop1 = 50;          % First Stopband Attenuation (dB)
+Apass  = 1;           % Passband Ripple (dB)
+Astop2 = 50;          % Second Stopband Attenuation (dB)
+match  = 'stopband';  % Band to match exactly
+
+% Construct an FDESIGN object and call its BUTTER method.
+h  = fdesign.bandpass(Fstop1, Fpass1, Fpass2, Fstop2, Astop1, Apass, ...
+                      Astop2, Fs);
+Hd = design(h, 'butter', 'MatchExactly', match);
+
+% [EOF]

hw6/feedback/chebyshev1.m

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+function Hcheb = chebyshev1
+	Fs = 44100;
+
+	Fpass = Fs/9;
+	Fstop = Fs/8;
+
+	Apass = 5;
+	Astop = 40;
+
+	specs = fdesign.lowpass(Fpass, Fstop, Apass, Astop, Fs);
+	Hcheb = design(specs,"cheby1",MatchExactly="passband");
+end

hw6/feedback/chebyshev2.m

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+function Hcheb = chebyshev2
+	Fs = 44100;
+
+	Fpass = Fs/3;
+	Fstop = Fs/4;
+
+	Apass = 5;
+	Astop = 40;
+
+	specs = fdesign.highpass(Fstop, Fpass, Astop, Apass, Fs);
+	Hcheb = design(specs,"cheby2",MatchExactly="passband");
+end

hw6/feedback/elliptic.m

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+function Hd = elliptic
+%ELLIPTIC Returns a discrete-time filter object.
+
+% MATLAB Code
+% Generated by MATLAB(R) 23.2 and Signal Processing Toolbox 23.2.
+% Generated on: 27-Mar-2024 18:58:12
+
+% Elliptic Bandstop filter designed using FDESIGN.BANDSTOP.
+
+% All frequency values are in Hz.
+Fs = 44100;  % Sampling Frequency
+
+Fpass1 = 6300;    % First Passband Frequency
+Fstop1 = 7350;    % First Stopband Frequency
+Fstop2 = 14700;   % Second Stopband Frequency
+Fpass2 = 17640;   % Second Passband Frequency
+Apass1 = 1;       % First Passband Ripple (dB)
+Astop  = 50;      % Stopband Attenuation (dB)
+Apass2 = 1;       % Second Passband Ripple (dB)
+match  = 'both';  % Band to match exactly
+
+% Construct an FDESIGN object and call its ELLIP method.
+h  = fdesign.bandstop(Fpass1, Fstop1, Fstop2, Fpass2, Apass1, Astop, ...
+                      Apass2, Fs);
+Hd = design(h, 'ellip', 'MatchExactly', match);
+
+% [EOF]

hw6/feedback/fortune_favors_the_fontaine.m

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+function noise = fortune_favors_the_fontaine(Fs, duration)
+	% make some noise
+	output = "";
+	while strlength(output) < Fs*duration
+		[ret dirty_snippet] = unix('fortune');
+		% clean
+		snippet = regexprep(dirty_snippet, '[^A-Za-z]+', '');
+		output = strcat(output, snippet);
+	end
+	noise = normalize(letters2numbers(convertStringsToChars(output)));
+end
+		% <+.03> what the fuck

hw6/feedback/letters2numbers.m

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+function num = letters2numbers(word)
+    asc = double( upper(word) );    % http://www.asciitable.com/
+    num = 26 + double('A') - asc;   % simple arithmetic
+end