Noise in Handel’s Messiah adding noises with random number generator

This is the assignment:

• Implement the following section of code to use a random number generator to add noise to the sample of Handel’s Messiah.
• Add noise in such a way that the music file is noise free after 7 seconds of music have passed
• Use subplot to plot the following in the same figure
• - the first 300 data points in the noise vector
• - the first 300 data points in sound_w_noise vector

But I genuinely have no idea where to start or where to go. I do not know how to do this assignment at all and the lecture notes were no help (also my professor doesn't like to email me back). This is what I have so far on the assignment....

%% Assignment 6 part 4
% Implement the following section of code to use a random number generator to add noise to the sample of Handel’s Messiah.
% Add noise in such a way that the music file is noise free after 7 seconds of music have passed
% Use subplot to plot the following in the same figure 
    % the first 300 data points in the noise vector
    % the first 300 data points in sound_w_noisevector
%% Load Handel's Messiah
load handel
sound(y,Fs);

pause

multiplier=0.10;
noise=randm(length(y),1)*multiplier;
sound_w_noise=y+noise;
%% Subplots

Answer 1

[John D'Errico]

Well, you did make some effort, sadly an unusual thing from many students. So a start. ;-(

clear
load handel
whos
 Name          Size             Bytes  Class     Attributes
  Fs            1x1                  8  double              
  y         73113x1             584904  double              

What Fs? What does it mean? If you read the help for sound, it is the sample rate for the sound vector in y, in samples per second.

So how many seconds of time does the entire song fragment encompass?

length(y)/Fs
ans =
           8.9249267578125

And how many samples will exactly 7 seconds require?

It is your homework. You need to do some thinking here, but this should get you started.

[Kylie Ellis]

This is what I added to my code, but I am not sure if I am doing the assignment correctly.

load handel           
sound(y,Fs);

pause

multiplier=0.10;
noise=randn(length(y),1)*multiplier;
sound_w_noise=y+noise;

sound(y+noise,Fs);
%% Subplots
t=1:length(y);
noisy = y + noise;

subplot(2,1,1);
plot(t(1:300),noisy(1:300));
title('Noise vector');
xlabel('Element Number in Music Array');
ylabel('Frequency');

subplot(2,2,2);
plot(t(1:300),y(1:300));
title('sound with noisevector');
xlabel('Element Number in Music Array');
ylabel('Frequency');

[John D'Errico]

I don't think you read what I said, or at least did not think about what I wrote.

length(y)
ans =
       73113
Fs
Fs =
        8192
length(y)/Fs
ans =
           8.9249267578125

So the sample rate is 8192 Hz, thus samples per second. The length of the clip is 73113 samples, so roughly 8.9249... total seconds of sound in that file.

What were you asked to do?

First, you were asked to contaminate the first 7 seconds with noise. How many samples would that be? (Hint: what is Fs*7?) Not the ENTIRE signal file, but only the first 7 seconds of it. How many samples of noise will you want to generate?

As for your code not producing a plot, I would suggest that you probably have multiple plot figures alive, and in the background. Make sure you close them all. A good command to learn is this:

close all

[Kylie Ellis]

It's not that I didn't "read what you wrote" or "think about what you wrote" it was just that I didn't understand it.

Given your equation of Fs*7, do I place it in the code like this:

sound(y+noise,Fs(7));

?

Fs*7 is 57344 and I'm not sure if I put that number in for the 7 or just keep the 7 in there.

I would like to point out that I am very unsure about what exactly this assignment is asking/means.

Also, thank your assistance so far.

[Kylie Ellis]

ok so I changed the beginning of the code to

load handel 
sound(y,(Fs*7))

noise=randn(length(y),1)*0.10;
sound(y+noise,(Fs*7));

and it is an extremely quick and high pitched version of the song/noise..and I am not sure if that is what I am supposed to do.

[Image Analyst]

Well it didn't plot because you got a pause in there and is waiting for you to hit a key, and then you messed up the subplot so it's blowing away your first plot. Plus you got the y label wrong. Y is amplitude, not frequency. Here is the fix:

load handel           

multiplier=0.10;
noise = randn(length(y),1)*multiplier;

% Subplots
t = 1:length(y);
noisy = y + noise;

% Plot noise-free signal.
subplot(3,1,1);
plot(t(1:300), y(1:300));
title('Noise-Free Sound');
xlabel('Element Number in Music Array');
ylabel('Amplitude');
grid on;

% Plot noise signal with no audio.
subplot(3,1,2);
plot(t(1:300), noise(1:300));
title('Noise Alone');
xlabel('Element Number in Music Array');
ylabel('Amplitude');
grid on;

subplot(3,1,3);
plot(t(1:300), noisy(1:300));
title('Noisy Sound');
xlabel('Element Number in Music Array');
ylabel('Amplitude');
grid on;

% Play both sounds one after the other.
sound(y,Fs);
uiwait(msgbox('When the music ends, click OK to hear the noisy audio'));
sound(noisy,Fs);

By the way, this looks a lot like Brandon's question.

[Kylie Ellis]

Thanks. Do I even need the pause in this code? Also, where should I edit the code so that the music file is noise free after 7 seconds of music have passed?