Arpangel wrote:Hugh, can I just chime in here and ask if the OP's question applies to an M&S pair?
He specifically mentions XY cardioids, so I don't think so, no!
I always set my cardioid mic about half an inch back from the front of the figure 8, as that's how I've always seen it done, with my MKH's anyway, any comments on this?
Obviously, this very much depends on the specific mics you're using, and the physical locations of the diaphragms in each mic.
With the Sennheiser MKH mics, the diaphragm in the MKH30 fig-8 is in sideways-on in the middle of the grille, so to align an MKH 40 or 50 (cardioid or hypercardioid) with that, the front of the grill would indeed be about 20-30mm back from the front of the MKH30, as shown below.
... But this wouldn't be the case if you were using a ribbon fig-8, or even a dual-diaphragm multipattern LDC, or example...
Mid-Side is a coincident technique, so the diaphragms of the two mics should, theoretically, be aligned vertically, one directly above the other. However, that's not always practical so if there needs to be an offset to make mounting the mics easier, the stereo imaging is more stable if the diaphragm of the Side mic is fractionally behind
the diaphragm of the Mid mic. So that the Side mic captures sounds fractions of a millisecond after the Mid mic.
If the Side mic is too far forward from the Mid mic, it captures sound first and so the leading transients in the stereo image start off 'out-of-phase' which creates the impression of an unstable image.