I need to find out the best way to set up microphones for simultaneously recording voice and instruments. I have been using a KSM44 for the vocal and a Rode NT5 for the instrument and placing the instrument mic about 15" away from the instrument and having the musician sing about 6" away from the vocal mic.
 
I am having a devil of a time getting any isolation. Right now, for the mandolin player, I am getting more mandolin in the vocal mic than in the instrument mic.
 
Is there any way to get better isolation?
 
Thanks in advance,
Tom
 

This is where mics with a fig8 pattern (like ribbon mics) are your friend as they have very good off-axis rejection and are easy to set up.
 
If you're limited in mic choice to cardioids you need to pay close attention to placement to maximise rejection.  Get them as close as you can, aiming directly at the source but aimed as far away from the bleed source as you can.
 
So have your vocal mic slightly below mouth level aiming up at the mouth, and the mandolin mic pointing down towards the sound hole(s)

Changing the players position can help as can different mic patterns...it can become a series of experiments until you find something that works best. Mandolins tend to command because they are the higher instrument and because of their unique sound. I think the main thing , although it sounds simple, is to get the mic the closest to the source and the furtherest from the offender if playing in a group and you want to be heard. I have the KSM44 and it's an excellent mic for this with plenty of patterns and a db reduction switch. There should be a way to move players and mics around to get the best sweet spot possible and this mainly involves monitoring while changing things.

Buy m auto align from Melda productions.

Try to put your Mics closer to the source than each other as much as possible. Preferably at least a 4:1 ratio.

One of my all time favourite great ways of doing this is with two figure of 8 mics.  See this article here but look down to the inage that is titled:  An improved setup using the two microphones in figure-of-eight mode.
 
http://www.soundonsound.c...articles/studiosos.asp
 
The two mics could even be adjusted slightly better.  Twist the top one so the diaphragm is on axis to the voice but the 90 degree null axis is pointing right down at the guitar.  Same with guitar mic, you can get it really pointing nice at the 12th fret but the 90 degree null point is aimed right up at the vocals.
 
You get strong separation with this approach.  But as the mics are picking up from the other side too it works better when you can face the performer into a deadened area.
 
The 90 deg null rejection of a figure 8 mic is quite exceptional and can be put to good use in the studio.