Noise Shaping Class

notes
This is an implemetation of a 9th order noise shaping & dithering class, that runs quite
fast (it has one function that uses Intel x86 assembly, but you can replace it with a
different rounding function if you are running on a non-Intel platform).  _aligned_malloc
and _aligned_free require the MSVC++ Processor Pack, available from www.microsoft.com.
You can replace them with "new" and "delete," but allocating aligned memory seems to make
it run faster.  Also, you can replace ZeroMemory with a memset that sets the memory to 0
if you aren't using Win32.
Input should be floats from -32768 to 32767 (processS will clip at these points for you,
but clipping is bad when you are trying to convert floats to shorts).  Note to reviewer -
it would probably be better if you put the code in a file such as NSDither.h and have a
link to it - it's rather long.

(see linked file)

Comments

  • Date: 2003-05-14 14:01:22
  • By: mail[ns]@mutagene.net
I haven't tried this class out, but it looks like there's a typo in the unrolled loop -- shouldn't it read "c[2]*EH[HistPos+2]"?  This might this also account for the 3 clock cycle improvement on a P-III.

// This arrangement seems to execute 3 clock cycles faster on a P-III
samp -= c[8]*EH[HistPos+8] + c[7]*EH[HistPos+7] + c[6]*EH[HistPos+6] +
c[5]*EH[HistPos+5] + c[4]*EH[HistPos+4] + c[3]*EH[HistPos+3] + c[2]*EH[HistPos+1] +
c[1]*EH[HistPos+1] + c[0]*EH[HistPos];

Great class! But I found one more mistake: function my_mod(9, 9) gives 9 instead of 0 (9 % 9 = 0).

HistPos = my_mod((HistPos+8), order);
EH[HistPos+9] = EH[HistPos] = output - samp;

 -> HistPos + 9 = 18 (max EH index is 17) which leads to out of array boundary and crash.

So my_mod should look like:

__inline my_mod(int x, int n)
{
    if(x >= n) x-=n;
    return x;
}