Common Techniques for Stereo Miking
Why stereo miking? Two reasons come to mind right away: positioning and ambience.
Stereophonic sound more closely matches the sound we hear with our own two ears because it offers the added dimension of positioning. Unlike a single mono microphone, stereo miking gives the listener sound images that correspond to the location of instruments in the recording session. Sounds that were on the left side of the stage are heard predominantly through the left speaker. Sounds that were on the right side of the stage are heard predominantly through the right speaker.
Additionally, stereo recording captures a lot more of the subtle acoustic details from the environment where the recording was made than mono miking can. In any enclosed space, sound waves reflect off the walls, the ceiling, the floor, and other surfaces. It's these reflections that help you form an audible impression of where you are. That's why a recording that's made in a locker room sounds different than a recording made in an office.
History of Stereo Miking
The technique of stereo miking had been invented a little before the 1930s, but at that time, Bell Laboratories in the US and EMI in the UK performed a lot of research on the number of recording microphones and playback loudspeakers needed to create a sense of realism for the listener.
It turned out that two microphones on the front end and two loudspeakers on the back end were the minimum, but they found out that different microphone arrangements produced different results. Below are four of the most common arrangement techniques.
4 Stereo Miking Techniques
The most basic technique is the spaced pair. This technique takes two identical microphones and places them on stands usually 3 to 10 feet apart. The distance will depend on the size of the musical group being recorded.
A spaced pair gives you a very open, spacious sound because the sound of the left-side players reaches the left microphone a little sooner than the right microphone. This time delay creates that extra spaciousness that most people like.
The downside is that the players in the middle of the stage sometimes don't sound quite right because they're being picked up by two microphones at the same time, and neither mic is directly in front of them. This causes some tonal variations and makes it a bit harder to tell exactly where the sound is coming from, so it's not quite as accurate.
X-Y Pair: Coincident Pair
In X-Y Pairs, two identical microphones are mounted together in one location one above the other. The position of the microphone heads and the angle between the microphones are both important here. There are a few different X-Y pairings, and the first we'll discuss here is the coincident pair.
In this arrangement, you mount the microphones so they're arranged in a horizontal V, with the bottom part of the V aimed at the stage. The heads of the microphones should be at the bottom of the V. Stack them so that they are as close together as possible in a horizontal arrangement. That way, the sound arrives at each mic at the same time.
A coincident pair gives you excellent positional accuracy. Because the sounds from the sides arrive at the same time, it's very easy to tell the location of each player on the stage. The downside is you don't get quite as much spaciousness, which can make the recording sound dry or dull depending on the acoustics of the room.
X-Y Pair: Near-coincident Pair
A near-coincident pair will provide more spaciousness. This technique uses two identical microphones mounted in a horizontal X.
There are different standards for the angle and distances between the mics, but one of the most popular is the French ORTF arrangement. This uses a 110-degree angle between the microphones with the microphone heads positioned six inches apart. This slight separation between the heads mimics the spacing between our ears, resulting in very good positional accuracy and spaciousness.
One of the most interesting stereo miking techniques is called mid-side or MS. In this technique, you use a cardioid microphone called the mid in the center and point it at the stage. It picks up the mono sound just like any microphone would. Then, use a bi-directional mic for the side mic. Position it just under the mid mic so it's facing left and right. The side mic picks up the ambience and positional information.
The signals from the mid and side mics go through a small matrix circuit that combines them in certain ways so that you get a left channel output and a right channel output.
You can make mid-side recording with two separate mics (one cardioid and one bidirectional) or one dedicated stereo mic that has two elements in it and the processing circuitry build in.
Because both the microphones are at the same point in space, a mid-side recording gives you excellent positional accuracy, so it's easy for the listener to visualize where the players are on stage. If you vary the level of the side mic, you can control the stereo image. In other words, you can control the amount of spaciousness, even in post-production. Plus, you only have to mount one microphone on a stand, which is both an easier setup and less distracting to the musicians and the audience.
Microphone Mounting Tips
You can use two different microphone stands, but if you want to make it easy, Shure makes a great adaptor called the A27M. This adaptor allows you to use one microphone stand and put two microphones on it while controlling the angle between the two microphones and the location of the microphone heads relative of each other.
Choosing the Right Stereo Miking Technique
Which one is right? It all comes down to personal preference and the source that you're trying to mic. If you're miking a small orchestra and you want a spacious sound, try the spaced pair. If you're just miking a couple of cellos in a small group, try the near-coincident pair. If you don't have much choice about where the mic stand can go at the venue, or you want to be able to remix the stereo image later, try a mid-side microphone or combination.
Check out our 40-page Microphone Techniques for Recording booklet for more information and ideas.
Editor's Note: This post was originally published October 12, 2007. It was updated March 23, 2017.