To RESHAPE the number of elements must not change.

vale is 1x1200;
nfft= 1024;                      % number of frequency samples
Navg= 8;                         % number of DFT's to be averaged
N= nfft*Navg;                    % number of time samples
n= 0:N-1;                        % time index
w= hamming(nfft);                          % window function
window= w.*sqrt(nfft/sum(w.^2));           % normalize window for P= 1 W
%
% Create matrix xMatrix with Navg columns,
% each column a segment of x of length nfft
xMatrix= reshape(vale,nfft,Navg);

Answer 1

[Walter Roberson]

vale is 1200 entries. You are trying to reshape it to be an array 1024 by 8. That cannot work.

[Walter Roberson]

% each column a segment of x of length nfft

You do not have a variable named x. If you did then you would use

xMatrix = buffer(x, nfft);

However I would suggest to you that you have a closer look at what you are doing. In nearly all cases I have seen of people using code similar to yours, what has been desired has been overlapping windows. To handle overlap of windows you would use buffer() with three parameters.

[Hari raj]

Thankyou sir,

nfft= 1200; % number of frequency samples

Navg= 9; % number of DFT's to be averaged

N= nfft*Navg; % number of time samples

n= 0:N-1; % time index

w= hamming(nfft); % window function

window= w.*sqrt(nfft/sum(w.^2)); % normalize window for P= 1 W

%

% Create matrix xMatrix with Navg columns,

% each column a segment of vale of length nfft

xMatrix= buffer(vale,nfft,Navg);

magsq_sum= round(nfft/2);

for i= 1:Navg

x_column= xMatrix(:,i);--------Index exceeds matrix dimensions.

xw= window(:).*vale(:); % apply window of length nfft

X= fft(xw); % DFT

X= X(1:nfft/2); % retain samples from 0 to fs/2

magsq= real(X).^2 + imag(X).^2; % DFT magnitude squared

magsq_sum= magsq_sum + magsq; % sum of DFT mag squared

end

when i apply im getting index exceeds matrix dimensions in the x_column.....how to solve sir?

[Walter Roberson]

You need to read the documentation on buffer(). The third parameter is the amount of overlap. It would be rare that the buffered signal happened to come out with exactly that number of columns.

To get out 8 columns from a signal of length 1200 buffered into 1024, then you need an overlap of 22 if I am awake enough to calculate properly.

[Hari raj]

Thanks for your reply sir......when in change my code and proceed my Navg =22

xw= window(:).*vale(:);

Matrix dimensions must agree error in this line.

window length is 1024x1

and vale is 1x1200

Kindly tell me how to solve this sir.

[Walter Roberson]

Do not multiply the window by the original signal. You multiply the window by the buffered signal. If you have R2016b or later that will just work nicely; if you have an earlier version you will need bsxfun as well.

[Hari raj]

what do you mean by buffered signal

[Walter Roberson]

xMatrix, the output of the the call to buffer()

[Hari raj]

ok thanks for your help sir....when i resolve im getting index matrix dimensions exceeds,

xw= window(:).*xMatrix(:);

window is 1024x1

and my xMarix is 1024x2

now how to multiply both of this sir

[Walter Roberson]

The : index like window(:) can never lead to that error (for numeric data types).

window.*xMatrix

Provided you are using R2016b or later.

[Hari raj]

Thankyou sir.... Its working fine.