I'm using the **Medium Size EQ** block and noticed that only 5 PRAM coefficients change when I move the sliders.

The wiki documentation says these are *General 2nd order filters* but the equations for said filters define 6 coefficients NOT 5.

So my question is: * What's the exact equation SigmaStudio is using to modify the 5 filter coefficients for the Medium Size EQ algorithm?*

Thanks!

-CT

Hello CT,

SigmaDSPs use an efficient implementation for second-order IIR filters which uses only one set of delays and which folds the six coefficients into five. Thus, SigmaStudio calculates the five coefficients A0, A1, B0, B1, and B2.

The legendary BrettG made a spreadsheet to calculate the five coefficients from the desired filter parameters. I have expanded this spreadsheet to handle additional filter types. You'll find it at EQ Low- and High-Shelf filter coefficients comming back - Mysterious S factor. Clicking on the spreadsheet cells reveals the formulas to calculate the intermediate results and the final coefficients.

One way to experiment with coefficients is to type them into the

IIR Coefficientdialog available in theGeneral 2nd Order Filter.Below are two filters, one set with the GUI, and one with coefficients calculated by the spreadsheet. They both show the same response.Notice that the filter's schematic shows the

coefficients with minus signs in front. Thus, when safeloading your coefficients from a microcontroller (but not when typing them into SigmaStudio's IIR Coefficient dialog), you'll need to flip youracoefficient's signs.aBest regards,

Bob