Recording - July 2012 - 58

placing the mics at the outside edges of the center third. This will probably be wide enough, or slightly too wide. If you hear sound mostly from the left and the right, with kind of a hole in the middle, then start moving the mics closer together. A pair of omnis or cardioids about 1 to 1.5 feet apart usually sounds great no matter what the width of the sound source. You are looking for a smooth stereo image from left to right, just like you hear in the room.

Spaced Arrays
This is when we use more than two spaced mics. For example, maybe you are recording a choir that is only 2 rows deep but 15 people wide. Maybe you’d like to have the mics no more than 5 feet from the singers to get a nice close sound but two mics just won’t cover the whole group. Divide the width into quarters and place three mics at the boundaries of the two center quarters as shown in Figure 5. Pan the mics left, center, and right, and use whatever polar pattern gives you the best balance of direct vs. room sound. If you feel you need even more mics, then divide the group into fifths and use four mics, and so on. [For an example of five mics across the width of a symphony orchestra, see our reports on Mike Pappas miking the Colorado Symphony, in our September 2010, February 2011, and May 2012 issues.—Ed.]

Figure 4

ORTF works with intensity differences the same way as XY cardioids, except that sounds arriving from the left also hit the left mic sooner that they hit the right mic, and vice versa. This is called time arrival difference and is a very important way that your brain figures out whether sounds are coming from the left or the right. With ORTF you will get a wider, more natural sounding stereo image. This is one of my favorite ways to record stereo! ~ NOS: Developed at Nederlandse Omroep Stichting (Dutch broadcasting organization). This is the same as ORTF but the mics are 30 cm apart and angled at only 90 degrees. It works better for larger ensembles like full orchestra. Mono Compatibility: Any time the mic capsules are not coincident there will be phase differences at different frequencies between the mics. If you start panning the left and right mics in towards each other, these phase differences may combine to produce an undesirable alteration in tone. So you might want to use a coincident pair if you think you might want to collapse the panning a bit.
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Spaced Pair Techniques (AB)
In a spaced pair, the mics are a foot or more apart and face straight ahead. This works well for wider ensembles like choirs, or when you need to be closer to your sound source and the other techniques don’t pick up the sound from the outside edges as well. Many engineers set up drum overheads as a spaced pair. This works the same way as near coincident pairs, involving intensity and time arrival differences. See Figure 4. Exactly how wide should this pair be? You can start by dividing the width of the sound source into thirds and

How high? How far?
To determine how far away to place a stereo pair in front of a sound source, I just try to keep the sound source within the 90 or 110 degree arc of an XY or ORTF pair. For spaced arrays and spaced pairs I try to make sure that every part of the sound source is within a 90 degree arc in front of one of the mics. Place the mics higher than the sound source, about 50% of the distance from the source. So if you are 6 feet away from a choir, place the mics 3 feet higher than the singer’s mouths. Experiment with going a bit lower and a bit higher and choose a height that sounds best. Figure 5

Recording - July 2012

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