A mono recording is pretty easy to make. You put up one microphone and hit record. The recording would give you a good but flat image of the instrument.
But what if you do not want mono, what if you like the open sound stereo gives you? Then ofcourse the obvious answer is to put up two microphones. And that is where the trouble begins. Which stereo setup should I use?
There are more ways than one to setup a stereo rig. For this article we will keep the number down to three. Stereo in its basics exists out of two things: intensity and phase. The here under presented setups make good use of both. And for demonstration purposes, every setup comes with audio examples. So you can decide for yourself which one you like best.
This setup is also known as intensity stereophony. They membranes pick up their signal at the exact same spot, so there is no phase difference between them. All audio is arriving at the same time. It is dependent of the direction the sound arriving. The microphones are placed at 90 degrees from each other and the capsules are crossed. One mic is looking to the left side and the other is looking to the right.
Looking at the image you can see there is quite an overlap of the two mics in the center of the setup. So you can expect that this setup delivers a fairly big focus on the center and somewhat weaker stereo information. This setup can be useful if you want your instrument to be stronger in the center and still want a stereo image.
Listen to this recording of a guitar in XY setup. The recording is straight from the DAW, no eq or dynamics have been added. The micsetup is placed at about one meter from the guitar.
In terms of mono-compatibility this would be the best choice, because of its strong center field.
ORTF originates from France (Office de Radiodiffusion Télévision Française, the french broadcaster). This standard states that your angle of mics should be around 110 degrees. There is also a Dutch version, which is called NOS (Nederlands Omroep Stichting). It has the same principles except for the distance between the mics. ORTF has 17,5 centimeters between the membranes and NOS has a distance of 30 cm.
If you look at the image the setup probably has more stereo information and less focus on the center, because of the lack of overlap in the middle area. This is a nice setup if you would want to record something that has to carry the leadvocal for instance. Or you have a larger group and you do not want a too heavy focus on the center.
Play this clip of the ORTF setup and listen to the difference in comparison with the XY setup.
The result is a wide, open sound. Also the recording has a less clear focus point; the direct guitar ‘voice’ is somewhat ‘drowned’ in the stereo information. Some might say that this setup has a ‘hole’ in the middle.
The last setup is the AB setup. This is also know as time-of-arrival(phase difference) microphony. Here the two mics are not in the same place but do look straight forward.
There is a lot of discussion on how wide the two microphones have to be to deliver a good image. Anything from 60 to 90 centimeters would be valid setups. The recording for this article was done at 70 centimeters distance between the microphones. Other than that it is a pretty straight forward setup. Point two mics straight ahead and hit record.
The example is a recording of an AB setup at about 1 meter from the guitar. The stereo image is more evenly spread across the whole stereo image. Unlike the XY which has a bigger focus on the center or the ORTF that gives you a ‘hole’ in the center.
This setup is great for use in front of a larger ensemble. While this can be your main setup, your recording can be more detailed if you would add microphones for individual instruments as well. This is very common to do with larger ensembles, as well as with orchestras.
Wide, wider, widest
After listening to these setups there is a simple list to make of which sounds the widest. The XY setup is not as wide as the ORTF and has a fairly strong center. But ORTF is not as wide as AB. Which one to use then?
Well, that totally depends on your needs. But to give you some guidance try to use XY in situations where you need the subject to sound good in the center and you need good mono compatibility.
Try using ORTF when you are recording more than one instrument and which is somewhat further away. AB is a technique that you can use to record choirs and orchestra. Although with an orchestra you probably want some close micing also for adding details.
Stereo close micing
Okay, so we listened to examples which were recorded at about one meter from the mic setup. Now what if you were to mic XY and ORTF up close to the subject? Would it still be useful? To show you what that sounds like, here are two recordings beginning with XY up close.
The result is a nearly mono signal. As told earlier XY is a intensity microphony setup which in this case proofs it. The microphones are so close to the subject it is nearly impossible for the mics to listen to different sides.
It is a bit like holding a flashlight and shining directly on your hand; your hand is lit but not the surrounding area. The light simply has no chance of shining elsewhere. So close micing in XY setup is not a real good idea.
The ORTF setup has its weaker center and this recording shows just that. The mic is only listening to what is left and right of the soundhole of the guitar. Listen to the recording.
On the right side your are hearing the body of the guitar, but the mic is missing the soundhole or the strumming of the hand. On the left side you are hearing ‘leftovers’. The mic is looking at the top of the neck, it virtually has no function. Again, a typically wrong usage of ORTF in this example.
Keep your distance
Stereo mic setups are brilliant if you use them correctly. Generally speaking, stereo setups works best when you maintain a reasonable distance between the microphones and the instrument. Close enough to catch direct signal, but far enough to catch the whole instrument or ensemble. Don’t use it the same way you do when are close micing. The more instruments, the more distance you are likely to need. The distance can vary between 70 cm up to a few meters.
You could also make combinations of a ORTF and a mono closemic which can deliver best of both worlds. The ORTF would be at a distance while your monomic would deliver the details. Do keep in mind that you can run into phase troubles between the two setups. So ask your artist to play and while moving your setup, listen to your headphones for the best spot of the microphones.