Help with Surf() Plot

Hi, thanks for reading. I have a university lab and I'm stuck on using a surface plot to display some data.

I have to read an audio file and apply a windowing process to it. The code (up to the relevent part) is below:

x = enframe(rm,window);
b = 0;

for i = 1:size(x,1)
a = fftshift(fft(x(i,:)));
a = abs(a);
a = ifft(a);
a = real(a);

b = [b,a];

end
b(1) = [];

rm is from the audio file and window is from the hamming() function. The for loop just runs through each element and stores it in a new array (then I get rid of the first element, which is just 0).

My problem is that my instructions tell me to 'Plot the 3D magnitude-time-frequency spectrum using the surf() command'. What I get at the end of this is 'b', which is 1x15360, the original rm is 15360x1, x is 120x128 (just 'rm' broken into windows of 128 length). I also have a time variable, 't', of 1x15360. I can't see how I could make these work together for a surface plot? If I have two axes of 15360, would I not then need Z to be 15360x15360 to make a surface plot? I feel like I have all the information I need but I've got no clue how to present it.

Any help would be much appreciated.

[Mehmed Saad]

You have following solution

1. Initialize b as empty and insert b = [b;a]
2. Initialize b equal to size of x and index it i.e. b(i,:) = a
3. if you donot want to follow above two steps, reshape b at the end of code with the dimension you instructor is telling you i.e. 128x120

[Chris Deakin]

Thanks for your help, but looking over it again I think I just don't understand what the question is asking me to do rather than not understanding the matlab function. I can plot things with your method above, but I'm sort of just plotting nonsense.

[Mehmed Saad]

you have to follow any 1 of the above three methods, no all of three at a time

after than

surf(b)

[Loren Patena]

hi, i'm also doing this lab, think we're in the same class, have you figured out about this one?

[Chris Deakin]

Hey, I couldn't figure this part out. I just put it in as surf(b) after I rearranged it, but I don't think it's right.

[Mehmed Saad]

please attach the audio file

[Loren Patena]

Hi, have you figured this one out?