Scott,
You really don't expect to place a mic 2 or 3 feet away from the singers mouth and not pick up some spill do you? There is really no way to avoid it. You can try getting the mic as close as possible to the guitar and aiming it downward, away from the singer but the results will still not amount to complete isolation.

This is a situation where you have to learn to "live with it". You have to make the bleed work for you not against you by futzing with placement of the guitar mic(s) and the vocal mic so you are not getting out of phase signals. You should reference the 3 to 1 rule in this case.

The 3 to 1 rule:
The 2 microphones must be at least 3 x the distance from each other as they are from the sound sources. So if the guitar mic is a foot away from the guitar, the vocal mic should be 3 feet from the guitar mic, if you're working in mono. In stereo, the distances may be more forgiving but if the audio is ever collapsed to mono playback, they will resurface.

Or you can record the guitar first and the vocal second.

But if you want to get a live take with vx and guitar, you are going to have to accept that there will be some spill in both mics.

Kurt nailed it; there's just no way you're going to be able to separate the two when done together. (and please, no, the answer is NOT more EQ.....if I had a nickle for every time that got suggested....)

If you're working with very close mic'ing, then phase issues will be minimal (folk guitarist/singer, for example.) You're vocal mic may end up masking the bleed into the guitar mic.

You may end up working with completmentary mics or even two of the same type, so the phase should be minimal anyway, or maybe even work to your advantage. You may also be printing each mic to a separate track, so you could also gently mix then in and out whenever there's singing vs. just guitar alone. (Add the vocal mic when they're singing, fade it out when not, etc. Should be easy enough to do in software with automation or cross-fades.)

Also, consider one mic for both. (Not unheard of, actually!) If you're working with a good large condenser mic, you may be able to experiment with placing the mic in the best position to get BOTH the guitar and the vocal. (Lomax made a career out of this, remember). I just did a session with an acoustic guitarist using some vintage instruments, with the goal of a/b'ing some LD mics. Turns out he wanted to SING as well, which I didn't expect.

We mic'd things up several ways, from one mic for each (voc & guitar) to one mic for both. We got great results either way, so never rule out happy accidents.

As always - you guys offer priceless advice. And I don't just say that because I wouldn't pay for it. :wink:

Really though - thanks for the input and the 3-1 guidelines spelled out. Kurt - I agree completely with your point about bleed being uncontrollable. Just the facts. Joe - no problem with EQ'ing. I'd rather leave stuff flat when it can work that way. But I once heard that if you drop out all the lows and max all the high's . . . :? Just kidding.

Thanks guys -

take care
Scott