Real cepstrum in loop

Hi

I have to compute a real cepstrum of .wav signal taking 20ms parts of signal, skip 5ms. Next I have to plot this in 3D using imagesc and mesh. My problem is in loop when I run rceps function.

My code is

[x,fp]=wavread('name_of_file.wav');
dr=4; %decimation level
fd=fp/dr;
y=decimate(x,dr);
Nd=length(y); %length of decimated signal
t=0:1/fd:(Nd-1)/fd;

next

d=floor(( ( ( ( (Nd-1) /fd) *1000) -20) /5)); %number of 20ms parts with skip
                                               5ms
for i=0:1:d
  g=y( ( ( ( ((i*5) +1) /1000) *fd):( ( ( ((i*5) +21) /1000) *fd) );
  %g=y(((i*60)+1):((i*60)+240)); %another method of cutting signal
  tab(i+1)=rceps(g);
end

After running this code I see an error

???  In an assignment  A(I) = B, the number of elements in B and
I must be the same.

Error in ==> my_file at 38
  tab(i)=rceps(g);

rceps function return real cepstrum of signal. Length of returning signal is the same as argument signal (in my case 20ms, 240 points).

I don't have enough experience to solve this problem, because this is my first time when I use loop in MATLAB and I don't know how to do this correctly.

Thank you for your time

Dawid

Answer 1

[Dawid]

Solution

tab=[];

for i=0:1:d-1
  g=y(((i*60)+1):((i*60)+241));
  c=rceps(g);
  p=c';
  tab=[tab; p];
end

Dawid

Answer 2

[David Young]

Your receps function returns a vector with 240 elements, and you are trying to assign these to a single element of tab. The error message is telling you that you can't put 240 numbers into a slot that only holds one.

Try assigning the vector to a row of tab rather than to a single element, like this:

tab(i+1, :) = rceps(g);

[Dawid]

Thank for your response. I modified code and now it looks like below

for i=0:1:d

g=y(floor( ( ( ( ((i*5) +1) /1000) *fd))):(floor( ( ( ((i*5) +21) /1000) *fd) )));

%g=y(((i*60)+1):((i*60)+241));

tab(i+1, :)=rceps(g);

end

but now I've got an error

??? Subscripted assignment dimension mismatch.

Error in ==> my_file at 34

tab(i+1, :)=rceps(g);

I've tried to declare tab

tab=zeros(143,240); %I've got 143 pieces

but it didn't change anything.

[David Young]

Could you have a look at the size of the result returned by receps:

r = receps(g);

disp(size(r));