[ERRORS] at ( Calculating Filter Coefficients to Store in a Microcontroller ) provided documentation.
Hi AD guys,
I have found errors on Calculating Filter Coefficients to Store in a Microcontroller documentation ( this link) , there errors is inside attachment 8244.Parameteric_5F00_EQ_5F00_IIR_5F00_Coefficient_5F00_Calculator.xls where formula for A1 and A2 are wrong, so please correct this.
Please check pdf content of document on same documentation article.
I found formula only for ( Peaking Filter Type ) can AD provides formula for other types that exists on Parametric Equalizer Param EQ window?
Thanks...
coefficient
microcontroller
filter
calculating
Hello Rocha,
Your finding is correct, the signs of the A coefficients needs to be inverted. This isn't an error, however. It stems from how SigmaStudio and the DSPs interact. Follow this reference https://ez.analog.com/dsp/sigmadsp/f/discussions/67437/calculating-filter-coefficients-to-store-in-a-microcontroller where it says:
Important: Because of the way the values are stored in RAM, the coefficients for a1 and a2 must be inverted from what is shown in the filter table generator.
A good way to test any coefficients you calculate is to enter then into the IIR Coefficient window of the General Second-Order Filter as shown below. This window inverts the A coefficients for you, so they can be entered as found by the coefficient formulas. Have your microcontroller flip the signs when safeloading the A coefficients.
Best regards,
Bob
Hi KJBob, thanks for anwser, can attach this testing project? i cant find this General Filter inside SS.
Hello,
The filter test project is for a ADAU1701, yet it really doesn't matter since you need not compile nor run on hardware to use the Stimulus-Probe tool. And you'll find the General 2nd Order Filter in the toolbox as shown: Then click on its center and choose the IRR Coefficient version in the drop-down box:
Best regards,
Bob
filter-test.zip
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