I do a lot of recording and music production with acoustic musicians. If a piece of music has acoustic guitar and vocals, the musicians often like to do the singing and playing together in the same take, rather than separately record the guitar track and then overdub the vocals. Doing it this way does keep the live and natural feel but I always get vocals bleeding into the guitar channel, however carefully I position the mics. I use an SE large-diaphragm mic for the vocals and an AKG C1000 with a cardioid pickup pattern for the guitar. I love the sound of the C1000 — but is there a similar small-diaphragm condenser that is hypercardioid, to reduce the amount of bleed?
Editor In Chief Paul White replies: Hypercardioids can be useful but are quite critical on positioning and tend to be less forgiving if the player moves around when performing, so I try to avoid using them in the studio whenever possible. They also have a vulnerable spot directly at the rear, where they can pick up unwanted sounds, so you must be careful where you aim the back of them.
I record a lot of acoustic players who want to sing at the same time, and providing the level of spill is low enough to allow you to get a good balance, it isn't usually a problem — as long as the spill isn't too coloured by the room sound. Hanging improvised acoustic absorbers around the playing area can help, the ubiquitous duvet being an obvious budget solution.
I'll often use an omni mic with an absorber behind it to capture the guitar sound — usually with the mic position below and in front of the the guitar body to the right of the player. Imagine the guitar is a Fender Strat and you're aiming the mic to look right down the jack socket from nine inches away and you won't be far off. The benefit of an omni mic is that the positioning is less critical, there's no bass boost if you work close up, and any spill comes across as more neutral sounding. That said, a cardioid can also produce perfectly acceptable results when used in much the same way.
Small-diaphragm condenser models generally work best for the guitar and large-diaphragm models for the vocals. You can still use your usual condenser mic for the vocals, ideally hung inverted just above the singer's mouth level and fitted with a pop shield. Try to get the singer to work fairly close up — six to nine inches or so — as this will keep the level of spill to a workable minimum. I find that this method still leaves you with some guitar spill in the vocal mic, but the guitar mic tends to pick up less spill from the vocals, as the position below the guitar puts it at a reasonable distance from the singer's mouth. This particular miking method also puts both mics at roughly the same distance from the guitar strings, so you shouldn't suffer any significant phasing when the two mic signals are mixed.
The other classic approach is to use figure-of-eight mics for both guitar and voice. The benefit of a figure-of-eight mic is that it is completely 'deaf' 90 degrees off-axis, so if you set up each mic so that the side axis points directly towards the sound source to be rejected, you'll get good separation — with the caveat that you have to take care to reduce unwanted sound getting into the rear of the mic. Duvet screens can help with this and commercial screens such as the SE Reflexion Filter also work well behind figure-of-eight and omni mics — as long as you don't get them too close to the mic. In all cases, maximising the physical distance between the mics as much as possible will reduce spill.