# Peaking filter and Notch filter coefficient formula

Hello guys,

I have some problem on calculate the Peaking and Notch filter.

In SigmaStudio wiki ( SigmaStudio Wiki ), I can not get both filter formula information,

and I reference the Robert Bristow-Johnson Audio Cook Book website (This : http://www.musicdsp.org/files/Audio-EQ-Cookbook.txt)

I found that the cook book contain the peaking filter formula, but I am not sure the value "alpha" what the calculation formula is. And I follow the cook book to generate the formula in my excel, I found the final value which I got is different with the SigmaStudio capture window value. So I want to ask, does there have the formula for the Peaking Filter and the Notch filter? because I have some function need to use IIR filter to implement.