Hi everybody,

i have a question about the calculation of Chebyshev or Notch cofficients **b0**, **b1**, **b2**, **a1** and **a2**. Where can i find the calculation? I've been looking in the SigmaStudio-Help but i found nothing about this topic.

Kind Regards

Eric

Hello Eric,

From your question I'm assuming you're planning to have a microcontroller figure or lookup coefficients and safeload them into your filters at run time. Otherwise, you need not handle coefficients yourself -- you could just enter the desired filter specs into SigmaStudio's

GeneralandNth-OrderFilters (the latter is not available yet for ADAU145x). If you do need to figure your own coefficients, you can calculate them using ordinary tools -- the process is a bit tedious but relatively straightforward.Calculating Chebyshev IIR coefficients is a several-step process. The first is to figure how many first-order and/or second-order stages you'll need to implement your desired response. This being analog theory (going back to the days of tubes!), you won't likely find it in DSP circles. Fortunately, ADI has a surprisingly good Web app which can help you with this. Please refer to https://ez.analog.com/message/225675#225675 for a link to this, as well as how to use it.

Once you have the gains, frequencies, and Q's for your filter stages, you could calculate each stage's IIR coefficients with a spreadsheet. Brett G. made the original one found at: Calculating Filter Coefficients to Store in a Microcontroller

I have expanded it to cover more filter types at: https://ez.analog.com/message/160192#160192

The final step is to convert the coefficients to a form suitable for safeloading. The tutorial at

https://ez.analog.com/message/61175#61175

is helpful for this.

Best regards,

Bob