find peaks.

hello, I have a plot of values from my fft function for a sinewave audio signal. I am now trying to analyze each peak in the plot to give me the sum of the peak and two other lower points on both sides of the peak. can anyone please help?

[God'sSon]

Hello,

This is the program I am trying to explain. After this is executed, how can I use the program to get the values of the peaks in the plot into my program?

N=2048;

fs=48000;

n=0:1:N-1;

F = fs*[0:N-1]/N;

w_a=sin((pi*(n'+0.5))/N);% calculate sine window

x1=w_a'.*sin(n*pi/24);

X1 = abs(fft(x1,N)).^2;

plot(F,X1)

Answer 1

[Laura Proctor]

Try FINDPEAKS:

[Xm Im] = findpeaks(X1)
Fm = F(Im)

The Fm and Xm values will hold your x and y values for the peaks.

[God'sSon]

thank you for your answer. but how do I find at least two other points on either side of each peak.

[Laura Proctor]

Im holds the index values, so to get the points on either side of the peaks, just use Im - 1 and Im + 1.

[God'sSon]

do you mean [Xm Im-1] = findpeaks(X1)

[Xm Im+1] = findpeaks(X1)?

[Laura Proctor]

Not quite...

[Xm Im] = findpeaks(X1)

iVals = reshape([ Im - 1 ; Im ; Im + 1],1,[])

xVals = F(iVals)

yVals = X1(iVals)

[God'sSon]

this works perfectly. thank you very much.