How to get last two bits except for LSB from audio signal in MATLAB?

Question

ayesha jabeen 2016-10-4

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/305703-how-to-get-last-two-bits-except-for-lsb-from-audio-signal-in-matlab

评论： Walter Roberson 2016-10-9

i have a code in which i am getting LSB values of audio signal now i am want to get last two bits except for LSB..Here is code:

    fid1=fopen('ash.wav','r'); 
    header=fread(fid1,40,'uint8=>char');
    data_size=fread(fid1,1,'uint32');
    [dta,count]=fread(fid1,inf,'uint16');   
    fclose(fid1);
    lsb=1;
    identity=[1 0 1 0 1 0 1 0]';
    dta(index)=bitset(dta(index),lsb,identity(1:8));
    dta(index)=bitset(dta(index),lsb,m_bin(1:10));
    index=([indices(19):indices(28)]);
    dta(index)=bitset(dta(index),lsb,n_bin(1:10));                              
    index=([indices(29):indices(28+len)]);
    dta(index)=bitset(dta(index),lsb,msg_bin(1:len)');

how to do it?

2 个评论
显示无隐藏无

michael 2016-10-4

Please write the complete code in a code format, so that it would be readable

ayesha jabeen 2016-10-5

编辑：Walter Roberson 2016-10-5

在 MATLAB Online 中打开

This is a code:

fid1=fopen([pathname filename],'r');
%first 40 bytes make wav header,store the header
header=fread(fid1,40,'uint8=>char'); 
%41st byte to 43rd byte,length of wav data samples 
data_size=fread(fid1,1,'uint32');
%copy the 16 bit wav data samples starting from 44th byte
[dta,count]=fread(fid1,inf,'uint16');   
%close the file only wav data samples are sufficient to hide the text 
fclose(fid1);
lsb=1;
msg='Hello how are you?';     
%run aurecover.m to recover this message from new2.wav file
msg_double=double(msg);     
  %convert it to double
msg_bin=de2bi(msg_double,8);  %then convert message to binary
[m,n]=size(msg_bin);          %size of message binary
msg_bin_re=reshape(msg_bin,m*n,1);  %reshape the message binary in a column vector   
m_bin=de2bi(m,10)';
n_bin=de2bi(n,10)';
len=length(msg_bin_re);       %length of message binary 
%len=m*n
len_bin=de2bi(len,20)';       %convert the length to binary
%hide identity in first 8 wav data samples.
identity=[1 0 1 0 1 0 1 0]';
dta(1:8)=bitset(dta(1:8),lsb,identity(1:8));
%hide binary length of message from 9th to 28 th sample 
dta(9:18)=bitset(dta(9:18),lsb,m_bin(1:10));
dta(19:28)=bitset(dta(19:28),lsb,n_bin(1:10));                              
%hide the message binary starting from 29th position of wave data samples
dta(29:28+len)=bitset(dta(29:28+len),lsb,msg_bin(1:len)');
%open a new wav file in write mode
fid2=fopen('new2.wav','w');

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Walter Roberson 2016-10-5

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/305703-how-to-get-last-two-bits-except-for-lsb-from-audio-signal-in-matlab#answer_237586

在 MATLAB Online 中打开

bitset(YourArray, bitset(YourArray, 2, NewBit2Array), 3, NewBit3Array)

3 个评论
显示 1更早的评论隐藏 1更早的评论

Walter Roberson 2016-10-5

Those arrays should be the same size as YourArray, and they should hold the new value to go into bit 2 for each corresponding location, and the new value to go into bit 3 for each corresponding location.

If you are only changing a single location, you still need to use the two bitset() calls. bitset() is not able on its own to realize that you want to change multiple bits in a single location, so you need to call it once for each bit position to be changed at the location.

Walter Roberson 2016-10-9

在 MATLAB Online 中打开

Opps, should be

bitset(bitset(YourArray, 2, NewBit2Array), 3, NewBit3Array)

请先登录，再进行评论。

Answer 2

Geoff Hayes 2016-10-4

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/305703-how-to-get-last-two-bits-except-for-lsb-from-audio-signal-in-matlab#answer_237343

在 MATLAB Online 中打开

ayesha - if

lsb=1;

and

dta(index)=bitset(dta(index),lsb,msg_bin(1:len)');

sets the least significant bit (lsb), then to set the bits before this one, you would just bitshift lsb to the left to modify the two bits prior to lsb. For example,

 % bit shift once to to modify the bit prior to lsb
 bitToModify = bitshift(lsb, 1);
 % bit shift twice to modify the bit that is two away from lsb
 bitToModify = bitshift(lsb, 2);

4 个评论
显示 2更早的评论隐藏 2更早的评论

Walter Roberson 2016-10-6

编辑：Walter Roberson 2016-10-6

bitset() returns a value rather than modifying the array in place, so you need to make those into assignments.

Also bitshift(lsb,2) would be 4 rather than 3 so you would not be storing into bits 1, 2, 3, but instead 1, 2, 4. The second parameter should just be a bit number in natural numbers.

ayesha jabeen 2016-10-6