If you'll recall, 3II3d00d, I had to come up with a slightly different formula for Excel to work correctly.  I'm not sure why our experiences different, but here's what I finally settled on for S:   S = (A^2*Q^2+Q^2)/(A^2*Q^2-2*A*Q^2+A+Q^2)   For A I used what comes from the Audio EQ Cookbook:   A = 10^(dBgain/40)   More specifically, I set up a spreadsheet where you input the desired dB gain in cell B1 and the target Q value in B2.  Then I have a formula for A in E1 and S in E2.  Here's