How can I calculate the energy of an audio file (audio signal) that I imported in Matlab?

I'm trying to calculate the energy of an audio file in matlab. I wnat to calculate its energy before and after filtering. Here's my matlab script:

clear('all');

close('all');

[f,fs] = audioread('test.wav');

N = size(f,1); % Determine total number of samples in audio file

figure;

subplot(2,1,1);

plot(1:N, f(:,1));

title('Left Channel');

subplot(2,1,2);

plot(1:N, f(:,1));
title('Right Channel');

n = 2;

fprintf('The sum of the absoulte values (Before filtering) is: \n');

fff = fft(f);

h = sum(abs(fff));

max(f)

disp(h)

beginFreq = 700 / (fs/2);

endFreq = 1600 / (fs/2);

[b,a] = butter(n, [beginFreq, endFreq], 'bandpass');

fOut = filter(b, a, f);

% Construct audioplayer object and play

%p = audioplayer(fOut, fs);

%p.play;

fprintf('The sum of the absoulte values (After filtering) is: \n');

figure;

plot(filter(b, a, f))

ggg = fft(f);

h = sum(abs(ggg));

disp(h)

fprintf('Sampling Frequency is: \n');

disp(fs)

[Image Analyst]

Wouldn't you use pwelch()?

Answer 1

[Frank Macias-Escriva]

In your code you will start approaching to your solution just fixing the mistyping on the calculation of "ggg", I mean, almost at the end of your script you should:

 ggg = fft(fOut);

instead of using "fft(f)". (in the last plot I would also use "plot(fOut)")

Anyway, you should check if you really want the energy of the discrete signal then you should look for:

sum(abs(fff).^2)/numel(f)

That Parseval's theorem states will be equal to "sum(f.^2)".

Consequently, for the filtered signal it will be:

sum(abs(ggg).^2)/numel(fOut)

again, it will be equal to sum(fOut.^2).

Hope this help.

Frank