I have two AKG Perception 420s, with three selectable polar patterns – cardioid, omnidirectional or figure-eight
 
What of the three settings should I use to capture only the cymbals, which I know is impossible?
 
What set up works best, for example XY (Coincident Pair), spaced pair etc. for a rock/instrumental.
 
Just want to get your opinions, thanks.

Cardiod if the ceiling is low.

You can try other settings if the room is large enough to have some contribution.

I just took down a pair of cadioid LDC and put up some figure 8 ribbons a few days ago.

I like changing it up and seeing what happens

There are a billion explanations describing OH mic placement out there. Try them all. :-)

I have hi ceilings...I think that is what you meant.
 
There is a lot of information out there. I just wanted to see what turned up here, thanks.

If you have the luxury of high ceilings, go omni!
 
I've not confirmed this experimentally, but I'm told the advantage of coincident versus spaced is better mono-compatibility.

If you have high ceilings then I'd encourage you to try the figure 8 setting.
 
I've been using spaced pair and using a string to make sure they are equidistant to snare top skin's center and also using a string to make sure they are equidistant to the bass drum's top of shell center.
 
Sometimes I like to align the spot mic tracks to the OH so the timing is tight and crisp. Sometimes I don't bother.
 
Coincident angles or M/S also work real well. Mono OH works real well.
 
I've been happy with getting a deep, deep boomy bass drum tone but I have finally decided it's time to start getting a beater track too because most people don't listen on a system where the super fat bass drum tone that I personally like plays back well. 
 
I just ordered some more new ribbon mics to try for a spaced pair as I like to use more OH than spot mic and get an in-the-room live sound and I am searching for just the right character... but a lot of folks use more spot mics and less OH.
 
My latest interest in ribbons is in the idea that you can compress the heck out of the OH and the cymbals end up just right. With mics that have a upper mid freq bump they make the cymbals brighter when you squash the OH with a compressor. Keep that in mind as you work on the placement of your 420's... what will the cymbals sound like when you are done mixing?
 
 
 
 
It really just depends on what you want and if you know what you want there are many ways to get there.
 
Hope you have fun with it!
 
best regards,
mike
 
 
 

The XY minimizes phase issues.
 
I prefer a spaced pair because it gives me an almost exaggerated sound stage (probably just my perception) ... perfect for rock.  Maybe less so for other genres.
 
Wrt to the phase issue, it can become apparent with cymbal washes so you need to be aware of it.  For example, if you want a cymbal crash to hang out there ... a phase issue will create a pumping sound (comb filtering???).  Bottom line is that you need to take the time to set-up a spaced pair to minimize any phasing issues.