Help Required With Graph Plotting in MATLAB

Question

I am about to present my work that I have created in MATLAB, but I am having trouble manipulating my data into a presentable form using the plot function.

My code looks like this:

[inputname, pathname] = uigetfile('*.wav', 'Select WAV-file');

thumb1 = inputname;               %# Get filename information
fprintf('\n%s is being turned into a 30s thumbnail...\n', thumb1);
fprintf('Please wait..!\n\n');
%# load the signal
[y, fs, nb] = wavread(thumb1);
y = mean(y,2);                               %# stereo, take avrg of 2 channels

%# Calculate frame energy
fWidth = round(fs*10e-3);                    %# 10ms
numFrames = floor(length(y)/fWidth);
energy = zeros(1,numFrames);
for f=1:numFrames
  energy(f) = sum( y((f-1)*fWidth+1:f*fWidth).^2 );
end

Basically I want to plot the energy of the track over time (in seconds).

plot(energy)

nearly does what I require, but I have an unusual amount of blank space at the end of the track which is not present in the .wav file alt text . This blank space is the main issue that I'm having. Ideally I would like the x axis to be displayed in seconds! Any help would be much appreciated.

edit1:

Using the first suggested method:

alt text

Edric · Accepted Answer · 2010-10-22 11:38:36Z

1

There's also

axis tight

which sets "tight" limits for the axis. See doc: http://www.mathworks.com/help/techdoc/ref/axis.html

answered Oct 22, 2010 at 11:38

Edric

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Oliver Charlesworth · Accepted Answer · 2010-10-22 11:14:18Z

1

By default, Matlab uses some heuristic rules to choose the limits of graph scales. You can override them with the xlim and ylim functions (e.g. xlim([0 length(energy)])).

If you want to plot against actual time, you can do something like:

t = (0:length(energy)-1) / fs;  % Timebase in seconds
plot(t, energy);

answered Oct 22, 2010 at 11:14

Oliver Charlesworth

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3 Comments

Velocity Over a year ago

That still isn't quite what i'm looking for i'm afraid. I've updated the original post with what it looks like using your suggestion.

Oliver Charlesworth Over a year ago

@Mark: Did xlim not do what you want?

Velocity Over a year ago

Sorry I totally glazed over that part. I apologise. @Edric's suggestion worked perfectly though, but thank you for the help.

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