Plotting a spectrum-like figure

Hello, I am aware of the spectrogram function of MATLAB. But I can't use that, and my question is I have three vectors-time, frequency, and energy of each frequency. I want to plot a figure where in x-axis I have time, in y-axis I have frequency and the energy of each frequency is visualized by different colors. Can you please explain how to plot?

[Martin Stump]

use the image or imagesc function like suggested here

https://stackoverflow.com/questions/13858807/how-can-i-plot-the-results-of-the-spectrogram-function

Answer 1

[Robert U]

Hi Tahmid Chowdhury,

From what you are describing you could have a look at contourf() https://de.mathworks.com/help/matlab/ref/contourf.html?s_tid=srchtitle and since there is the need of a grid instead of vectors for x- and y-axis you should have a look at meshgrid() https://de.mathworks.com/help/matlab/ref/meshgrid.html?searchHighlight=meshgrid&s_tid=doc_srchtitle.

Kind regards,

Robert

[Robert U]

Here just a small example out of matlab:

contourf(peaks(20),256,'LineStyle','none')

Answer 2

[John BG]

Hi Tahmid

This is John BG <mailto:[e-mail] [e-mail]>

You don't want to use spectrogram because not enough time lines, right?

Perhaps you would like to use one of the following

1.

[x,y] = meshgrid(-3:.5:3,-3:.1:3);
z = peaks(x,y);
figure;ribbon(y,z)

2.

figure
[X,Y,Z] = peaks(30);
waterfall(X,Y,Z)

3.

Lawrence has built a ceptstral GUI that seems to match the tool needed to compare those 3 time-vectors mentioned in your question

.

download available here

.

https://uk.mathworks.com/matlabcentral/fileexchange/52094-cepstral-waterfall?s_tid=srchtitle

4.

https://uk.mathworks.com/matlabcentral/fileexchange/52094-cepstral-waterfall?s_tid=srchtitle

https://uk.mathworks.com/matlabcentral/fileexchange/7463-waterfall-fft?s_tid=srchtitle

if you find this answer useful would you please be so kind to consider marking my answer as Accepted Answer?

To any other reader, if you find this answer useful please consider clicking on the thumbs-up vote link

thanks in advance

John BG

<mailto:[e-mail] [e-mail]>

Answer 3

[Tahmid Chowdhury]

Hi Robert and John, Thank you for your feedbacks. I certainly did learn new things from you both.

However, what I am looking for is an image like this-(please see attached)

This is basically the plot of- --a time vector --10 column vectors of frequencies, where each column represents frequencies of one intrinsic mode function at time t --10 column vectors of energies, where each column represents the energies of the frequencies of one intrinsic mode function.

I know how to compute these functions and how to calculate the energies and frequencies. But my concern is the plotting.

[Tahmid Chowdhury]

PS-just wanted to add, the colormap represents the energy of each frequency.

[Robert U]

Hi Tahmid Chowdhury,

if you know how to calculate the energy of each frequency at any time than you "just" have to provide the following data:

• grid X containing the time values,
• grid Y containing the frequency values
• grid Z containing the corresponding energy

Then, you can try different plots (some presented in this thread) and choose whichever you like most.

Contour-Plots:

https://de.mathworks.com/help/matlab/contour-plots-1.html

Surface and Mesh Plots:

https://de.mathworks.com/help/matlab/surface-and-mesh-plots-1.html

Spectrogram itself utilizes "surf" ( https://de.mathworks.com/help/matlab/ref/surf.html ; see YourMatlabRootPath\toolbox\signal\signal\spectrogram.m).

Kind regards,

Robert

Answer 4

[Jan]

Perhaps you mean:

time = 0:100;   % Test data
freq = 0:30;
data = rand(numel(freq), numel(time)) .^ 2;

surface(time, freq, data, 'EdgeColor', 'none');
colormap(jet)

[John BG]

It's not this, it's a spectrogram Tahmid asks for.

MATLAB already has the command spectrogram.

[Jan]

Tahmid wrote: "I know how to compute these functions and how to calculate the energies and frequencies. But my concern is the plotting." and he knows spectrogram already.