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