I see that some of the large-diaphragm condensers
offer a fgure-8 option. What is the purpose of
figure-8 on an LDC?
How about putting an LDC right between a singer and an
instrumentalist when the mic is set to figure 8?

It can also be used as a "duet mic" so that 2 (or more, I suppose) singers can face each other and follow each others' cues. Some time getting the balance right is important, I'd guess.

No reason it can't be used the way you mention, for a more naturalistic recording. So many people like to isolate everything completely that I'm not sure how many might use it that way, but I've got recordings that were done that way--they catch a more blended, natural (and more "musical") sound. I like it.

Figure-8 is great for two person narratives because a booth is usually a small space for two people. Going from 2 mics to 1 means elimination of any time phasing and comb-filtering issues (harshes up the sound) especially important with overlapping dialog (because you can't just pan tracks in post).

Also, while I've never done this, figure-8 used to be a primary narrative mic pattern even for one talent. Apparently, before dead recording standards for narrative, figure-8 was highly regarded for a natural sounding room and voice. I'm not sure what kind of room, but perhaps not a totally dead one such as we like these days.

Also, while I've never done this, figure-8 used to be a primary narrative mic pattern even for one talent. Apparently, before dead recording standards for narrative, figure-8 was highly regarded for a natural sounding room and voice. I'm not sure what kind of room, but perhaps not a totally dead one such as we like these days.[/QUOTE]
Now that's something I had never heard of.

Quite common to use two fig 8s, one on top of the other, upside down, rotated 90 degrees - performs in a similar manner to a coincident pair of cardioids, but the extra rear pickup adds a new dimension to the sound, especially in less than perfect venues - the rear pickup is also good for capturing audience response. Hails from the old BBC technques when stereo first appeared.