How can we determine how many peaks are at each plot?

How can we determine how many peaks are at each plot?

Answer 1

[Sulaymon Eshkabilov]

Use findpeaks() fcn: see DOC

e.g.:

t = linspace(0, 2, 1000);     % Time
fs = 1/t(2);                  % Sampling freq [Hz]
f1 = 5;                       % Freq 1. 
f2 = 25;                      % Freq 2.  
f3 = 50;                      % Freq 3. 
f4 = 100;                     % Freq 4.  
% Signal generated with some noise effect
S = 5*sin(2*pi*t*f1)+2*cos(2*pi*t*f2)+1.5*sin(2*pi*t*f3)+.5*cos(2*pi*t*f4)+.1*randn(size(t)); 
% FFT caclculations:
L = length(S);
n = 2^nextpow2(L);
Y= fft(S, n);
f = fs*(0:(n/2))/n;
P2 = abs(Y/n);
P1 = P2(1:n/2+1);
P1(2:end-1) = 2*P1(2:end-1);
plot(f,P1) 
title("FFT")
xlabel("f (Hz)")
ylabel("|P(f)|^2")

Peak_Freq_Values_ALL = findpeaks(P1);
figure(2)
findpeaks(P1,f, 'MinPeakProminence',.25,'Annotate','extents');
title("FFT with Peak Freq values")
xlabel("f (Hz)")
ylabel("|P(f)|^2")