This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

IIRCAS5 coefficients

Hello all together,

I have tried to designed a second order low pass filter using Filter Design Toolbox and exported the SOS to my workspace. fA =500Hz, cutoff frequency 38Hz aiming a higher order after testing

The coefficients are 1    2    1    1    -1.3406    0.5095
Gain

0.0422
1

After that I tried to find the five right fixed point coefficients for IIRCAS5. The problem is now that there are numbers that are greater than 1.
So in Q1.14 the coefficients are (no sign change necessary?)

DATA h_iir[5*NBIQ] ={
  -21965,     /* -1.3406... - a1 */
  32767,     /* 1.999...  - b1 */
  8347,        /* +0.49...  - a2 */
  16384,    /* 1.000...  - b2 */
  16384     /* 1.000...  - b0 */
};

My problem is now that a0 is implicated 1 and can not be changed. So the 10Bit (unscaled) data is not processed correctly.

So what is the right way to convert from Matlab SOS to the fixed point coefficients for IIRCAS5?
The problem has been described here before:

http://groups.google.com/group/comp.dsp/browse_thread/thread/8598e8ceb7f0157/ff5f1ada3ce2601b