Imagine you are listening to an acoustic jazz band, a choir or an orchestra. Sounds good, doesn't it?
So what would be the simplest and most obvious way of making a recording so that it sounds exactly like you hear it?
Well, you could position two microphones on either side of a head-shaped object and place it exactly in your listening position. The microphones will then hear what you hear. The recording should be perfect.
Except it isn't. This technique is known as 'binaural' or 'dummy head' recording, but it only sounds good when played back on headphones. It doesn't work on loudspeakers. On loudspeakers the sound image is confused and not at all pleasant to listen to. And certainly nothing like you heard in real life.
So because the most obvious solution doesn't work, we have to turn to other methods. None of these methods are perfect and each involves care, compromise, and an 'instinct' for finding the right locations for the microphones.
So where do you start?
Well let's simplify the situation down to one instrument and one microphone. How should you position that one mic?
Firstly, place the musician in the room where he or she sounds best acoustically. This is part of the recording engineer's role to do this.
Next, find the best place to listen from, still purely acoustically. Wander around the room, closer and further away. When you have done this, you have a starting point. So place the microphone there.
How high should the microphone be? Well, as high as your ears would be a good starting point. There's no reason to go higher or lower yet.
And which direction? Well, pointing at the instrument. There are very few occasions where you would not point the mic directly at the instrument.
If everything sounded good to your ears, it will already sound quite good through the microphone.
But there will be one problem...
It will sound over-reverberant, more distant than it sounded acoustically.
The reason for this is that the brain processes the signals from the ears and can 'filter out' too much reverberation. Since the microphone is totally lacking in intelligence, it cannot do this. It picks up everything within its coverage angle.
So nearly always you will need to place the microphone closer. Don't change anything else, just move in closer. Half the distance would be a good starting point. Then listen again.
Through a process of repeated repositioning and testing you will find the optimum distance to achieve the most natural sound.
Now, if you wish, you can experiment with height. Instruments normally sound their best on the horizontal plane. That's now we naturally hear them, and that's how we expect them to sound.
But the microphone might pick up more of the reflection from the floor than the ears, in combination with the brain, would. So raising the microphone may help. Try it and see. Don't leave the microphone raised unless you can hear a distinct improvement.
So these are the five rules that form the basis of all microphone technique, and can be extended to multiple instruments. You don't have to follow the rules always, but you won't go wrong if you do...