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Q value of filter

Question asked by Philip on Mar 30, 2011
Latest reply on Apr 13, 2011 by BrettG

I am playing with the second order general filter in my adau1701.

 

I generate a noice input from PC, passing though the 1701 and back to the PC. Then I plot the freq response in the PC

I use the sigma studio to calculate  two set of filter coeff

1) freq=15000, gain=-16, q=1.5 (as sigma_studio setting.jpg, correct me is I am wrong)

2) freq=1000, gain=-16, q=1.5

 

And I have two question about that:

1) By looking at the 1k filter freq response, the peak and the freq cutoff relation is not matching with the normal filter relation.

  I use the calculator(http://www.sengpielaudio.com/calculator-cutoffFrequencies.htm) and get the high freq cut off should be at around 1.3kHz while I  end up with the high freq cut off at 1.1kHz

 

2) By comparing the 1k filter and 15k filter with the same q, it seem the 15k filter is more narrow then the 1k filter. Is that a reason behind?

 

I am very new to those filter's, correct me if I doing somethings that didn't make sence

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