%take the fourier transform
xdft = fft(x);
xdft = xdft(1:length(x)/2+1);
% create a frequency vector
freq = 0:Fs/length(x):Fs/2;
% plot magnitude
figure(2)
semilogx(freq,20*log10(abs(xdft)));
xlabel('f(Hz)');
title('FFT of signal');

%locs is now in frequency
[pks,frqs] = findpeaks(abs(X),freq);
figure(3)
plot(xdft(locs), pks, 'or')