1

I have a pre-designed in-series 14th-order IIR filter in second-order sections. Problem is, when I simulate and measure the behavior in my codec, there is a frequency shift downward (as compared to the MATLAB prediction). Is there a simple way to alter the coefficients in such a way to shift the center frequencies of each band? Thank you.

panthyon
  • 1,133
  • 12
  • 25
  • Do you need to shift the frequencies or scale them by a factor? – Olli Niemitalo Sep 14 '15 at 15:24
  • Is this the same problem as in this question? http://dsp.stackexchange.com/questions/19225/audio-eq-cookbook-without-frequency-warping – JRE Sep 14 '15 at 15:27
  • JRE, I don't think so. The 14th-order SOS filter I've been provided with does not use RBJ. @Olli, I don't know, I can't tell if the shift is necessarily uniform from 0 to Fs/2. I'm trying it by hand first. – panthyon Sep 14 '15 at 15:36
  • OK, but could it still be subject to the kind of warping that was mentioned, with maybe a similar solution? – JRE Sep 14 '15 at 15:46

1 Answers1

1

The problem was an incorrect sampling rate issue, as a lower sampling rate than the designed rate caused the center frequency shift downwards. Today I learned something about the relationship between sampling rate and IIR coefficients (there is a proportional relationship between sampling rate and center frequency).

Peter K.
  • 25,714
  • 9
  • 46
  • 91
panthyon
  • 1,133
  • 12
  • 25