Can some one please tell me how to find the maximum amplitude frequency of the ecg signal? I have attached below my code. I keep getting maximum frequency at 0 Hz.

function [freq,SSAS,freq_max] = tutorial10
% Read in the data file
filename            = 'data.csv';                                    % Filename
delimiterIn         = ',';                                              % Entries are comma delimited
headerlinesIn       = 0;                                                % No header
ecgData             = importdata(filename,delimiterIn,headerlinesIn);   % Read the file into an array called ecgData

% Calculate (but don't plot) single-sided amplitude spectrum (this includes points along frequency axis, and amplitude axis)

% Determine frequency which exhibits maximum amplitude 

% Set up for FFT

T = 1./360;                          % Sample time
Fs = 1/T;                             % Sampling frequency
L = length(ecgData);                             % Length of signal (total samples)
t = (0:L-1)*T;                        % Time vector

%Calculate the FFT of the ecg data

NFFT = 2^nextpow2(L);                 % Next power of 2 from length of signal
Y = fft(ecgData,NFFT);
ecgData =ecgData -mean(ecgData);
SSAS =2*abs(Y(1:NFFT/2+1));   


%Construct the points along the frequency axis

freq = Fs*linspace(0,1,NFFT/2+1);  
max_a= max(Y);

idx = find(Y == max_a);
freq_max = freq(idx)



% Create filter
Fcutoff=30;
order=2;
cutoff=2*Fcutoff/Fs;







end

Answer 1

[Peng Li]

try

Y = fft(ecgData - mean(ecgData), NFFT);

It is expected that the DC contains most of the energy of the signal. You could explictly remove this DC component, or you can try something like detrend to remove the nonstationary trend which is usually quite common in physiological data.

[Peng Li]

Besides, the implementation of finding max is not elegant. max is supposed to give your the index as well

[max_a, idx] = max(Y);
freq_max = freq(idx)

[Siratul Srotoshwini]

[Siratul Srotoshwini]

I keep getting this error? Can you please tell whats wrong? Thanks.

[Peng Li]

I guess you should use max(SSAS) instead of max(Y). Y is complex. SSAS based on your codes is amplitude spectrum.