Matlab Program to Filter ECG Signals Assignment Solution

Instructions

Objective

Write a program to filter ECG signals in matlab.

Requirements and Specifications

Source Code

clc, clear all, close all %% First, load the signal load ecg_person_1.mat % Store the signal in a variable named 'y' y = ecg_person_1; % Plot signal figure(1) plot(tm, y) xlabel('Time (s)') ylabel('Magnitude') grid on %% Question 2: Get duration of signal % We were told that the signal is recorded with 500 samples per second so % to get the total duration of the signal we just need to divide the total % number of samples by 500 Tf = length(y)/500; fprintf("The signal has a duration of %.2f seconds\n", Tf); %% Question 3: Standard frequency % The standard frequencty of ECG signals can vary between 0.5Hz to 100 or % 150 Hz [1] %% Question 4: Spectral Analysis % let's plot a frequency spectrum analysis to check the main frequency % on the signal and see if there are other frequencies % Frequency spectrum % Time step dt = tm(2)-tm(1); % Sampling frequency Fs = 1/dt; % Fast Fourier Transform Y = fft(ecg_person_1); % Length of signal L = length(ecg_person_1); P2 = abs(Y/L); P1 = P2(1:L/2+1); P1(2:end-1) = 2*P1(2:end-1); f = Fs*(0:(L/2))/L; figure(2) plot(f,P1) title('Single-Sided Amplitude Spectrum of ECG Signal') xlabel('Frequency (Hz)') ylabel('Magnitude') grid on % From the graph, we can see that the main frequency on the signal is 50Hz. % We can also note that the signal has a lot of low-frequencies noise, so % we now know that we need to filter these low frequencies. We can also see % that the signal has frequencies of 150 Hz. This kind of noise is caused % by the muscles when reading the ECG signals, so we will apply a bandpass % filter to keep only the frequencies near 50 Hz %% Question 5: Design a bandpass filter to filter frequencies higher than 100 Hz % First, we remove the trend from the signal. We assume a trend of a 4-th % order polynomial. We assume this because after trial-and-error, this % value returned a signal with the trend removed yf = detrend(y,4); % Now, we remove noise yf = medfilt1(yf, 10); % Now, we remove the low frequencies [yf,d] = bandpass(yf, [20,70], Fs); % Get transfer function % Plot figure(3) plot(tm, y) hold on plot(tm, yf) legend('Original', 'Filtered') xlabel('Time (s)') ylabel('Magnitude') grid on % Frequency spectrum of filteres signal [b,a] = tf(d); H = tf(b,a) % Now, show Frequency Spectrum of the filtered signal % Fft Y = fft(yf); P2 = abs(Y/L); P1 = P2(1:L/2+1); P1(2:end-1) = 2*P1(2:end-1); f = Fs*(0:(L/2))/L; figure(4) plot(f,P1) title('Single-Sided Amplitude Spectrum of Filtered Signal') xlabel('Frequency (Hz)') ylabel('Magnitude') grid on %% References % [1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4624499/#:~:text=Modern%20ECG%20machines%20record%20ECG,Hz%20as%20an%20industry%20standard.