MATLAB: Adding white noise to a wav file??? URGENT!

Question

Hi,

I need to add white gaussian noise to a wav file. I've managed to do this by adding the two together

 freq = 9000;
 duration = 0.4;
 S2 = rand(1,(freq * duration));
 S1 = audioread('drum.wav');
 S = S1;
 S(1:length(S2), 2) = S2;
 soundsc(S)

but the sound signal in the wav.file when they are both played together turns into a really low distorted pitch. I understand now that if i was [y,fs] = audioread('drum.wav') then it will play normally but im not sure how to add white noise to this??? I have tried several ways but nothing seems to work apart from the above which distorts it!!

please help!!! URGENT!!

 * I preferably want someone using the program to change the white noise using some kind of Standard Deviation so i dont want to just use awgn*

Answer 1

You didn't use randn and you didn't pass in the frequency. Try this:

% Open standard demo sound that ships with MATLAB.
[perfectSound, freq] = audioread('guitartune.wav');
% Add noise to it.
noisySound = perfectSound + 0.01 * randn(length(perfectSound), 1);
% Find out which sound they want to play:
promptMessage = sprintf('Which sound do you want to hear?');
titleBarCaption = 'Specify Sound';
button = questdlg(promptMessage, titleBarCaption, 'Perfect', 'Noisy', 'Perfect');
if strcmpi(button, 'Perfect')
  % Play the perfect sound.
  soundsc(perfectSound, freq);
else
  % Play the noisy sound.
  soundsc(noisySound, freq);
end