Is centredFFT function really exist?

i try to run this code that i get from a website. however, the MATLAB cannot read the "centeredFFT" whenever i try to enter this line: function [X,f] = centeredFFT(x,Fs); it will return this line: ??? Undefined function or method 'centeredFFT' for input arguments of type 'double'. may i know what is the reason behind this?

i am thinking that i need to use extra toolbox, which i don't know its name.

below is the code

[y,Fs,bits] = auread('bird_chirping2.au');

x = y(:,1);

clear y; N = length(x);

time = [1:N].*(1/Fs);

han = plot(time,x); xlab = xlabel('Seconds'); ylab = ylabel('Amplitude'); grid on; set(han,'LineWidth', 2); set([xlab, ylab],'FontSize', 24, 'FontName', 'Times'); set(gca,'FontSize',20,'FontName','Times','Fontweight','Bold')

% wavwrite(x,Fs,bits,'test.wav');

[X,f] = centeredFFT(x,Fs);

figure; han1 = plot(f,abs(X)); axis([-8000,8000,0,max(abs(X))]); grid on; xlab1=xlabel('Frequency(Hz)'); ylab1=ylabel('|X[k]|'); set(han1,'LineWidth', 2); set([xlab1, ylab1],'FontSize', 24, 'FontName', 'Times'); set(gca,'FontSize',20,'FontName','Times','Fontweight','Bold')

% sound(x,Fs,bits);

% % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % %

fc = 2000; fNorm = fc / ( Fs/2); [b,a] = butter(10, fNorm, 'low'); x_Low = filtfilt(b, a, x);

figure; freqz(b,a,bits,Fs/2); grid on;

% sound(x_Low,Fs,bits); % wavwrite(x_Low,Fs,bits,'x_Low_.wav');

[X_LOW,f_low] = centeredFFT(x_Low,Fs);

figure; han2=plot(f_low,abs(X_LOW)); axis([-.8e4,.8e4,0,max(abs(X))]); grid on; xlab2=xlabel('Frequency(Hz)'); ylab2=ylabel('|X[k]|)'); set(han2,'LineWidth', 2); set([xlab2, ylab2],'FontSize', 24, 'FontName', 'Times'); set(gca,'FontSize',20,'FontName','Times','Fontweight','Bold')

figure; han3=plot(time,x_Low); grid on; xlab3=xlabel('Frequency(Hz)'); ylab3=ylabel('|X[k]|)'); set(han3,'LineWidth', 2); set([xlab3, ylab3],'FontSize', 24, 'FontName', 'Times'); set(gca,'FontSize',20,'FontName','Times','Fontweight','Bold')

Answer 1

[Youssef Khmou]

hi Nadiah , no its not built-in function, but wherever you found the program you must find the related material.. here is the function you are looking for :

 %===============================================================
 %%taken from e80 course at Harvey Mudd College

 function [X,freq]=centeredFFT(x,Fs)
 %x is the signal that is to be transformed
 %Fs is the sampling rate

 N=length(x);

 %this part of the code generates that frequency axis
if mod(N,2)==0
    k=-N/2:N/2-1; % N even
else
    k=-(N-1)/2:(N-1)/2; % N odd
end
T=N/Fs;
freq=k/T;  %the frequency axis

 %takes the fft of the signal, and adjusts the amplitude accordingly
 X=fft(x)/N; % make up for the lack of 1/N in Matlab FFT
 X=fftshift(X); %shifts the fft data so that it is centered
 %========================================================================

For friendly use function, try my Submission :

http://www.mathworks.com/matlabcentral/fileexchange/40002-psd-power-spectral-density-and-amplitude-spectrum-with-adjusted-fft

[Nadiah]

ok now i understand. I need to setpath to use the function right? thank you.

[Youssef Khmou]

yes , you manage that , put it in \Documents\MATLAB

Answer 2

[Thorsten]

Can Matlab find your downloaded function?

   which centeredFFT

If not, move your function to your current directory or another directory in Matlab's search path.

[Nadiah]

it says 'centeredFFT' is not found. how can i move the function to the current directory?

for this syntax, in what Toolbox it is used?