Is it possible to save audio sample values from alteration while using wavwrite function of matlab?

Hello, I am manipulating values of audio samples for audio steganography.When i have my manipulated audio sample object, i want to write it as a new audio file using wavwrite. But when i create object of this newly created audio file, i find sample values different from the previous values of samples which i had manipulated.

Is there any method to control wavwrite function in order to keep my sample values as same as these were before wavwrite?

Answer 1

[Image Analyst]

You're either writing out the same, original audio data, not the altered data like you thought, or you're reading in the same original audio data, not the altered file.

[manisha sharma]

My original audio object is 'y':

>>y=wavread('C:\Users\HIM\Desktop\audio stegno\strings.wav');

>>y(1:7)

ans =

1.0e-003 *

Columns 1 through 6

                   0                   0  -0.213623046875000   0.091552734375000   0.305175781250000   0.305175781250000

Column 7

   0.213623046875000

After manipulating it, i get new audio object 'y_enc' with values:

>>y_enc(1:7)

ans =

1.0e-003 *

Columns 1 through 6

                   0                   0  -0.212620000000000   0.091453000000000   0.304180000000000   0.304180000000000

Column 7

   0.212620000000000

Now i use wavwrite to create an audio file from this 'y_enc' like this:

>>wavwrite(y_enc,44100,'s.wav');

Now make another object from this "s.wav" file:

>>d=wavread('s.wav');

And i get sample values of 'd' as:

>> d(1:7)

ans =

1.0e-003 *

Columns 1 through 6

                   0                   0  -0.213623046875000   0.091552734375000   0.305175781250000   0.305175781250000

Column 7

   0.213623046875000

These values are not matching with those i have written using 'y_enc' but matching with original object 'y'.

Please tell me where i'm lacking?

Thanks in advance....

[Image Analyst]

This works just fine for me:

y=wavread('guitartune.wav');
y(1000:1007)
% Make y_enc
y_enc = y;
y_enc(1000:1007) = 0.5;
y_enc(1000:1007)
% Write it out.
wavwrite(y_enc,44100,'s.wav');

% Now make another object from this "s.wav" file:
d=wavread('s.wav');
d(1000:1007)
delete('s.wav');

ans =
    -0.010437
    -0.010132
   -0.0099792
    -0.010193
    -0.010223
    -0.009552
   -0.0086365
    -0.007843
ans =
          0.5
          0.5
          0.5
          0.5
          0.5
          0.5
          0.5
          0.5

ans =
          0.5
          0.5
          0.5
          0.5
          0.5
          0.5
          0.5
          0.5

What did you do differently?

[manisha sharma]

I'm having problem.Probably because i'm working with large number of digits after decimal in samples.

Please try this:

My original audio object is:

>> y=wavread('C:\Users\HIM\Desktop\audio stegno\strings.wav');

>> y(1:7)

ans =

1.0e-003 *

         0
         0
   -0.2136
    0.0916
    0.3052
    0.3052
    0.2136

New audio object created:

>> y2=y;

>> y2(1:7)=0.0005;

>> y2(1:7)

ans =

1.0e-003 *

    0.5000
    0.5000
    0.5000
    0.5000
    0.5000
    0.5000
    0.5000

>> wavwrite(y2,44100,'k.wav') >> s=wavread('k.wav'); >> s(1:7)

ans =

1.0e-003 *

    0.4883
    0.4883
    0.4883
    0.4883
    0.4883
    0.4883
    0.4883

Values of samples changed in object 's'.

I want that values of samples in 's' should remain same like in 'y2'.

[Image Analyst]

I don't know that much about it. I wouldn't think doubles would have much of a problem out in the 5th decimal place but maybe it does. Or maybe it has something to do with encoding it at 44100. Can you try other rates?

[manisha sharma]

As you asked i tried it at different frequencies like 88200,10000,1000 and so on. But it still causing problem.

I have no idea what to do next.Please help if you can.

Thanks...

[manisha sharma]

Okay finally i got the way to do it.This time i have chosen the bits in wavwrite as '32' like this:

>>wavwrite(y_enc,44100,32,'new_audio.wav')

It is working for me.

I think this can be helpful for others having the same problem.