quantisation using matlab

How can i quantize decimal numbers with fractional parts(like 3.111112,1.22213) to specified number of bits using matlab?

[Knut]

I believe that you could do something like the code below, given that you first decide on some scaling/range of your signal:

%clip

x(x<0) = 0;

x(x>1 = 1;

%round

N = 8;

y = round(x*(2^N-1));

Answer 1

[Walter Roberson]

Are you using the fixed point toolbox? I did request in your previous question that you make that clear when asking about fixed point numbers. (Is that previous question answered to your satisfaction? If so then you should Accept the answer.)

If you are not using the fixed point toolbox, then let F be the number of bits to code in the fraction. Then, calculate

round(x * 2.^F)

and encode the resulting integral value in to the total number of bits.

Be sure to take in to account the encoding of the sign, whether it be through separate sign, 2's complement or other encoding (something you need to specify... a point which I believe I conveyed in response to your newsgroup posting.)

Answer 2

[fit institute]

Thank you Roberson.......yes,I have fixed point toolbox....

I need to quantise the dctmtx(6) to 8 bit hexadecimal values

dctmtx is given below

>> dctmtx(6)

ans =

    0.3536    0.3536    0.3536    0.3536    0.3536    0.3536    
    0.4904    0.4157    0.2778    0.0975   -0.0975   -0.2778   
    0.4619    0.1913   -0.1913   -0.4619   -0.4619   -0.1913    
    0.4157   -0.0975   -0.4904   -0.2778    0.2778    0.4904    
    0.3536   -0.3536   -0.3536    0.3536    0.3536   -0.3536   
    0.2778   -0.4904    0.0975    0.4157   -0.4157   -0.0975    
    0.1913   -0.4619    0.4619   -0.1913   -0.1913    0.4619   
    0.0975   -0.2778    0.4157   -0.4904    0.4904   -0.4157

how this can be done ? 1)by using fixed point tool box 2)without using fixed point toolbox

can you explain please?(with codes)

Answer 3

[Walter Roberson]

Without, 5 bits of fraction, 2's complement applied to the entire number.

>> M = [0.3536    0.3536    0.3536    0.3536    0.3536    0.3536    
    0.4904    0.4157    0.2778    0.0975   -0.0975   -0.2778   
    0.4619    0.1913   -0.1913   -0.4619   -0.4619   -0.1913    
    0.4157   -0.0975   -0.4904   -0.2778    0.2778    0.4904    
    0.3536   -0.3536   -0.3536    0.3536    0.3536   -0.3536   
    0.2778   -0.4904    0.0975    0.4157   -0.4157   -0.0975    
    0.1913   -0.4619    0.4619   -0.1913   -0.1913    0.4619   
    0.0975   -0.2778    0.4157   -0.4904    0.4904   -0.4157];

>> dec2hex(typecast(int8(M * 2^F),'uint8'))
ans =
0B
10
0F
0D
0B
09
06
03
0B
0D
06
FD
F5
F0
F1
F7
0B
09
FA
F0
F5
03
0F
0D
0B
03
F1
F7
0B
0D
FA
F0
0B
FD
F1
09
0B
F3
FA
10
0B
F7
FA
10
F5
FD
0F
F3