Calculate Q factor of a Low Shelf and High Shelf filter
it looks like this eq10q uses cascaded parametric EQs, initially set up to be bell, but switchable to other types (like shelving).  

i wouldn't doubt that they're using the audio EQ cookbook.  if you're using that, there is a parameter called "shelf slope" or $S$ that is often set to 1, because that gets you the steepest slope without dips or lips or bumps.  so it's a straight incline or decline to the shelf level.  if the control is $Q$, instead, there is a relationship between $S$ and $Q$: 

$$ \frac{1}{Q} = \sqrt{ \left( A + \frac{1}{A} \right) \left( \frac{1}{S} - 1 \right) + 2} $$

where

$$ A = 10^{dB_\text{gain}/40} $$

and $ dB_\text{gain} $ is the shelf gain in dB.

i would just plug in $S=1$ and get a $Q=\frac{1}{\sqrt{2}}$.