When EQ tool generates shelf filters, what Q are they?

[jb123]

It seems like this row is Q? Though I don't see a label anywhere that says it's Q. But the Q for the shelf filters is not given. Is it 0.707? 1.0? Something else? 1.0 seems to match best when I try it.

 

[John Mulcahy]

The Generic and Extended equalisers are based on the Robert Bristow-Johnson 'Cookbook' equations. The shelf filters are specified internally using a slope parameter, which has a value of 1 for the maximum monotonic slope for a 2nd order filter, but the equivalent Q for a Generic or Extended HS Q filter is 0.7071. Other equaliser shelf filter implementations may use different formulations and give different results for the same parameter values.

 

[jb123]

OK I plotted my own RBJ implementation and overlaid the other software and confirmed that the REW shelf is S = 1 or Q = 0.707, while SigmaStudio's shelving filters are actually using "S" even though it says "Q factor". So "Q factor" of 1.0 produces the steepest monotonic response in that software.