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Low frequency Bandpass IIR filter in fixed 32 format

Question asked by anoopcheckingin on Jan 10, 2013
Latest reply on Jan 21, 2013 by SachinV


    I am trying to design an low frequency Bandpass IIR filter with the following filter spec

Fstop1 : 0.19

Fpass1 : 0.21

Fpass2 : 38

Fpass2 : 42

With BF533 Processor (Visual DSP++ 5.0 Update 8).


After dabbling with FIR which resulted in very high filter order values I started looking on to IIR which gave me a much manageable order value to work with, so chose implementing it with df1IIR. I generated the coefficients for the same using Matlab FDATool (filter was shown to be
stable) as 

  • IIR Elliptic filter
  • Minimum order (16 in my case)
  • df1 Second Order Sections
  • Double precision float values for the


I had tried using the fixed point 16 bit but the filter was shown to be unstable so moved over to fixed 32 bit and passed the corresponding values to the blackfin processor BF533 (C Header).

Referring to your earlier post Problem with IIR Filter for Blackfin I have been using the coeff_iirdf1_fr32 for the purpose of converting the float values to fixed values. Though in Matlab I was able to obtain the desired output I am not able to do so for simulation in Vdsp++ for BF533.

Please help me with the same.