If you can't get a good performance from your vocalist, it could be your method of monitoring that's at fault. Paul White offers some helpful advice.
It's all too easy to overlook the fact that the standard of a vocal performance can depend heavily on the type and quality of monitoring provided for the performer. There's a tendency just to give the singer a pair of cans with a rough backing mix set up, and then leave her/him to get on with it — but this is unlikely to prompt the best possible performance.
There are several factors which affect a vocalist's ability to pitch and perform properly, one of which is monitoring level. I favour the type of system that allows the performer to control the overall level of his or her monitoring from within the studio or vocal booth. Although most mixers come with elaborate foldback systems, I usually find it just as easy when recording a lone singer to feed them the control mix as it is to feed them a foldback mix — and at least I know then that they're hearing exactly the same thing as I'm hearing. I can also constantly monitor their headphone balance, and even though the ideal monitor mix might not have quite the same balance as the final mix, that isn't usually a problem when you're overdubbing.
As a rule, singers need to be able to hear both the rhythm of the track and an instrumental mix that will help them pitch their notes most accurately. This might mean bringing up the level of the pad keyboard part or the rhythm guitar, while pulling stabs and sound effects back a bit; in the case of backing vocals, the singer also needs to be able to hear the existing vocal parts clearly. None of this need be radical, however, and a slight readjustment of the control room mix is usually all that's needed.
The type of headphones used by the singer can also make a difference to your end result. Although semi‑open headphones usually provide the most accurate sound, they don't give as good a degree of isolation as fully‑enclosed models. Whether a little spill from the cans is going to cause problems is really down to you to decide; if the vocals are going to be used solo at any stage, then spill from the backing tracks needs to be kept to an absolute minimum, but in most instances, a little spill is not a major problem. Some singers find it easier to work with one headphone on and the other off, and if this increases the spill level unacceptably, you can always pan the headphone mix to one side, or even wire up a set of phones with one side disconnected. If you don't want to tamper with your headphones, you can achieve the same result by making up a simple adaptor. This uses two 47Ω resistors to sum the left and right stereo channels to mono. If you have the facility to provide a mono feed, omit the resistors and leave either the red or black core of the cable disconnected.
Aside from the headphones, spill into the vocal mic can often be traced to sound leakage from the control room — the isolation between the control room and studio leaves much to be desired in many home studios and small commercial facilities. The only way around this is to turn the control room monitors down as much as is practical while recording, and in extreme cases, the engineer may need to resort to headphones during recording.
Some singers just can't work with headphones, and in this case, the only alternative is to use loudspeakers for monitoring. This obviously raises the question of spill, but in situations where a modest degree of spill isn't a problem, you can get away with keeping the mic fairly close to the vocalist and setting up a speaker (or pair of speakers) behind the mic, in much the same way as you would live. You'll need to use either a cardioid or hypercardioid mic to make this work properly, and the monitor needs to be positioned in the 'dead' area of the mic, where it picks up little or no sound. It is also important to position an absorbent surface behind the singer, to minimise the amount of sound reflected back into the 'live' side of the mic. Even after you've taken these precautions, the monitoring level should still be kept as low as possible.
A more effective solution is to use the 'out‑of‑phase' monitoring trick, which involves sending an identical mono foldback mix to two speakers, one of which is wired out of phase with the other. If a microphone is placed anywhere on an imaginary line equidistant from the two speakers, the sound fields will largely cancel each other out, resulting in very little spill. The mic position is critical, and the best way to do the final adjustments is to listen to the mic channel using headphones while you play the backing track. As you move the mic, you'll hear the spill level change, and it doesn't take long to find the spot where there's minimum sound.
Using out‑of‑phase monitors in the above way is a well‑known, tried and tested technique which has been used by professionals for many years, but how can it be applied to stereo recordings? The problem is that stereo recording relies on the use of two microphones, either in different places or pointing in different directions — which means that only one of the pair can be in the right position to benefit from out‑of‑phase monitoring. There's no complete solution that I know of, but if you're working with an ensemble and don't have any artistic objections to recording the part twice to thicken it up, there is a way around the problem — record your stereo vocal part using just one mic!
To do this, you set up the mic and speakers as usual, but then position the performers such that the mic's position relative to them is the same as it would be if it were one of a stereo pair. If you are trying to simulate a spaced‑pair stereo miking setup (where the sound source is recorded by two mics placed in parallel a short distance apart), this might simply involve the ensemble shuffling a couple of feet to the left of centre. Once the track is recorded, the singers move the same distance to the other side of centre, and overdub the same part on another track. With any luck, when the two tracks are replayed simultaneously, and panned hard left and right, the result will not only be in stereo, but will also be richer, because each voice has been captured twice. If you're simulating a coincident miking setup (where the two mics are placed at the same point, facing the sound source at right angles to one another), you need to move the performers around the mic in an arc, so as to maintain a constant distance from the mic.
Finally, you may want to make a true stereo recording without double‑tracking everything, in which case there is a solution, but only if you have lots of tape tracks to play with and a mixer that offers phase reversal. In this case, you set up your stereo pair of mics in the studio with the monitor speakers behind, just as you would for a stage performance. Record the vocal performance to tape, complete with spill, then remove the singers and record just the monitor spill onto another two tape tracks. Now comes the interesting part. Play back both the vocal tracks and the spill‑only tracks (both panned to their correct left and right positions), but with the mixer's phase reverse buttons down on the 'spill' tracks. Once the levels of the tracks are matched, the spill should largely cancel out, though you may have to adjust this independently for the left and right parts to get it perfect. In theory, the degree of cancellation is likely to be higher if the performers remain in their original positions during the recording of the spill‑only tracks, but what you gain in separation, you may lose in additional breathing and shuffling noises. Once the result is as good as you can get it, bounce it onto another pair of tape tracks, leaving the original four free for re‑use.
Once you've tried these techniques and convinced yourself that they work, you'll probably be able to come up with variations of your own to suit your own working methods. If you can minimise the level of spill at source, that's fine, but in situations where you have to use monitor speakers in the studio, these tricks can save the day.
It's well known that reverb in the cans is very helpful in extracting a confident performance, and can also help with accurate pitching. What is less well known is that too much reverb can put the singer off just as much as too little, so once you've set up a level you think is OK, ask the singer if he/she would like more or less of it.