Basic Matlab FFT

fft_demo.m

%% Trial FFT
% http://www.mathworks.co.uk/help/matlab/math/fast-fourier-transform-fft.html

fs =  48000; % Sample Rate
n  =  4096;  % Power of 2 number of samples/ length of FFT

% Get/Generate data
 t = 0:1/fs:10-1/fs;                % 10 sec sample
 x = (1.3)*sin(2*pi*15*t) ...       % 15 Hz component
   + (1.7)*sin(2*pi*40*(t-2)) ...   % 40 Hz component
   + (2.5)*randn(size(t));

%# Frequency Bins
bins = (0:1:n-1)*(fs/n);

y = fft(x,n);

%# plot fft
% plot(bins, abs(y));
% title('FFT')
% xlabel('Frequency (Hz)')
% ylabel('Magnitude')

plot(bins, 20*log(abs(y)));
title('FFT')
xlabel('Frequency (Hz)')
ylabel('Magnitude (dB)')