A guide to stereo microphone techniques – part one
By Rob Sandall
| Posted in Music Technology
Stereo microphones – oft referred to, seldom explained. Many a fantastic result has been achieved by the application of a good stereo microphone technique, but surprisingly few ‘bedroom’ engineers have been given the tools they require to really make the most of the technology. And no wonder – there’s a lot of learning to be done before you can consider yourself an expert in the dark art, and much of that process revolves around experimentation to find what works for you.
Indeed, this three-part guide to getting started in the stereo world should not be considered the definitive word on how stereo micing should be done, but rather a collection of general rules, all of which can and should be broken if doing so nets you a ‘better’ – or more appropriate – sound.
However, as always, you’ve got to know the basic rules before you can break them. So if you’ve never tried to use a stereo mic pair on a recording before, then here’s everything you need to get started.
The basic concept behind stereo microphone technique is to recreate, sonically, the true position of instruments and or people in a room. If the drummer is playing to the left of the microphones, and the flautist is on the right, then the engineer positioning his stereo mic set wants the listener to know it. In some circumstances this can sound a little too roomy, but a lot of the time you’ll find natural layers of sound, depth, and a pleasant stereo feel.
So what makes a recording sounds stereo? Bizarrely, inaccuracy of a sort. The stereo effect is created by doubling up, which we can hear by very subtle time inconsistencies between the two signals, as well as level differences. Effectively, you are aiming to pick up two separate inputs that are almost, but not completely, the same. You have a number of options to achieve this, the first and simplest of which is spacing.
By spacing I mean taking two cardioid microphones and separating them by, let’s say, a couple of feet, with both pointing straight ahead. Recorded to a stereo channel, this means that sound created anywhere other than dead centre will reach one of the microphones before the other, depending on where it is in the room.
Our brains will interpret that sound when we listen to a track, and will be able to understand where the instruments ‘are’ – to the left or right, or in the middle. The downside to this is that those instruments dead centre will be represented much more clearly than those to the left or right in the image. When the mics are spaced further apart, you’ll get a warm, ambient kind of sound, which might be harder to place in the mind’s eye (or ear), but which will arguably sound more ethereal.
A good way of approaching spacing is to think logically about the sound source that you’re positioning. For example, if you position a mic directly in front of an acoustic instrument so that it sounds much more prominent than the electric guitar which you’ve positioned off to the far left, then that might sound a touch unrealistic. Of course, that might be what you’re aiming for, but creating natural placement in the stereo image will piece together a band in a listener’s mind. Mixes can – if done well – sound more ‘live’ than live recordings.
But, as with anything, there are compromises to be made in using this technique. To find out more, read part two of ‘A guide to stereo microphone techniques’ tomorrow.
Tags: matched microphone pair, recording in stereo, stereo microphone placement