Video: 5 Stereo Mic'ing Techniques—XY, Mid/Side & More

Today we are going to dive into stereo pair techniques involving the use of two microphones to simultaneously record a stereo image for that rich, wide sound.

Mono signals from each microphone are assigned to the left and right channels of a stereo track to create a sense of width in the recording that is absent in one-channel mono recording, or that would later fall apart if the two signals are summed into one channel. They have been developed to avoid frequency phasing issues and to achieve a richer stereo image. This will help the listener feel like they are in the room with the source.

With each stereo pair technique, there will be a difference in volume level, timing, and frequency balance. A difference of just a few milliseconds is enough to create a stereo effect. By angling the microphone in different directions in relation to the instrument, each microphone will pick up a slightly different balance of frequencies.

You may have heard of the word "coincident" when researching these techniques. It means that the microphone capsules must be placed close and sometimes slightly above each other. This means placing the capsules of the microphones as close together as possible. XY, Blumlein, and mid-side techniques use a coincident pair of microphones. With coincident pairs, timing is not affected due to the mics being the same distance to the sound source.

If you are using a mic pre, you would need to run each microphone channel through the same model of preamp with the same amount of gain applied to the signal.

Spaced Pair (AB)

First, we are going to talk about spaced-pair. This is where two mics are set some distance apart in parallel or angled. Usually small-diaphragm condensers are either in omni or the cardioid polar pattern. [Need a primer on polar patterns? Follow the link.]

Point both mics toward the instrument, usually at a distance of a foot, and spaced three feet apart. (Anywhere from three- to 10-feet apart works.) This describes the 3:1 ratio rule, which we will talk about soon and helps with mono compatibility.

Compared to the other stereo techniques we describe below, a spaced pair typically provides the widest and most dramatic stereo image with less room acoustics but more chances for error, since the mics are farther apart.

This is often used for large sound sources like mic'ing a grand piano, an entire drum kit, full bands, or for capturing "room sound." For an orchestra or a choir captured by distant mics, AB is pretty much the main go-to setup.

There are two potential problems with AB spaced-pair recordings: phasing and overstretching, with a dead zone in the center. The distance with the mics mean that sound waves can arrive at different times and therefore are more prone to phase cancellation, especially when mixed down to a more narrow soundstage or to mono.

This can be mitigated by using the "3-to-1 Rule," which says that you can minimize comb filter and other phase issues by making sure that the distance between the two mics is a 3:1 ratio, with the shorter distance being from the mic to the source. The other issue with AB is that if the mics' distance apart is very large, the stereo image will seem artificially overstretched, with a dead zone in the center.

Small-Diaphragm Condensers

XY Technique

Let's discuss the XY stereo pair. This one may be the most used, easy, and reliable stereo recording technique. Mic directional diaphragms are positioned at the same point in space, so there will be no differences in timing. This is the opposite of AB mic'ing and creates the most "narrow" stereo image compared to the other stereo pair techniques.

The two mics are typically angled at 90º and aimed so that the mic on the left captures the right channel and the mic on the right captures the left channel, usually with small diaphragm condensers. Two cardioid microphones are typically used, and the angle can be as big as 135°.

The techniques will only have differences in frequency balance, which prevents issues with mono phase cancellation. Best used in close mic'ing applications and smaller rooms to provide a clear but not too wide stereo image with the most minimal phase issues, this technique is also great for sound effects, small outdoor applications, and Foley sound.

Blumlein Pair

The Blumlein pair uses this same positioning as XY but with two figure-8 mics rather than two cardioids in XY. This captures room sound from behind the source and adds a different sense of spaciousness and realism. Note that you can also create one figure-8 pattern using two cardioid mics, so you would need four cardioid mics for the Blumlein technique.

This technique is named after the inventor of stereophonic sound, English engineer Alan Dower Blumlein. The idea for this setup came from his work with antennas (spotting submarines during WWII). His idea regarding the antennas was to take advantage of both level and phase to describe signals in a 360° view.

This was originally created using ribbon microphones in the 1930s. A few types of mics were built specifically for the Blumlein technique, including the famous Royer ribbon mics.

Try placing the mics off to one side of the room or toward the back rather than the front or center. Common uses are for drum overheads, piano, orchestral ensembles, and full bands.

Mid/Side (Written MS, M/S, or M-S)

The technique has a middle or center mic pointed at the sound source set in cardioid or sometimes the omni pickup pattern, usually using a small diaphragm condenser, while a large diaphragm condenser figure-8 mic picks up the sides.

You then split the side mic signals by sending it to two mixer channels, pan each hard right and hard left, then phase invert one of those two signals. Mix in the main center "mid" channel with the stereo side channels to adjust the width. The greater level of the sides compared to the mid, the greater the stereo width. This would be very similar to how our ears pick up sound.

One of the more complicated pair techniques, but it has more mono compatibility and the least amount of phase issues. It also gives the most spread flexibility in width without adding any reverb.

Identical matched pair is unnecessary for only this technique. Because the stereo information comes from only one mic in a bi-directional or figure-8 polar pattern, there is no need for the mid mic to be the same model or size, as long as the volume levels match.

Common uses include close drum rooms and overheads, acoustic guitar, string sections, piano, ambient room sounds, nature or field recordings, small vocal groups.

Note that the Zoom H2N is the only all-in-one portable handheld recorder with five built-in mics and many stereo pair techniques options, including mid-side.

Large-Diaphragm Condensers

Near-Coincident (ORTF, aka side-other-side and NOS)

Near-coincident mic'ing, named after ORTF, an acronym in French for Office Radio Television of France and NOS, the Dutch Broadcasting Organization. Radio broadcasters developed this setup.

The backside of the microphones that are near touching, rather than the front-side making the name near-coincident techniques. This technique combines the principles of AB and XY but has the width of the spaced pair and the strong mono compatibility of the X/Y technique, without the disadvantages. Usually small diaphragm condensers are great for this technique in picking up less ambient room sound.

They vary slightly in mic distance and angle; in ORTF, the cardioid mics are angled outward at 110º and separated by 17 cm (6.7"), whereas in NOS, the mics are 30 cm (12") apart and angled at 90º. Fun fact, the ORTF pair distance resembles the distance between the human ears at 6.7".

Like XY coincident pairs, the near-coincident pairs should be placed closer to the sound source. These techniques are a fabulous starting point for pianos, small orchestra ensembles, and percussion instruments, drum kits and overheads, choir, field recordings, and even a solo acoustic instrument. The NOS technique is the go-to for pianos.

Honorable Mentions

Binaural dummy head is a favorite honorable mention, with two small diaphragms set in omni or lavalier mics in your own ears. It's a different technique, showing how we perceive sound, and uses an actual dummy head with two microphone capsules built into the ears. Each person's ears are like a fingerprint. It will capture the room sound unique to your ear shape.

Decca Tree is three micss set in omni positioned in a "T" pattern, creating an equilateral triangle traditionally using the Neumann M 50 small diaphragm tube condenser commonly done for a large orchestral or choir performance, though it can also be used for drum room mics.

DIN stereo is the same as NOS but with a shorter mic distance of 7.8", rather than 11.8".

To conclude, if you are ever confused about how far to place the pair from the sound source, just visualize in relation to where the mic is aiming to the left and right edges of the sound source, as though it were a photo image.

Use the mono switch button if provided on your mixer. You can go back and forth between stereo and mono and listen for phase cancellation. It will sound thin, or the volume will be lower on certain instruments or frequencies, or it may even disappear completely. Just adjust your mic until it sounds rich. Also be aware of the proximity effect in bass frequencies.

Remember to get a stereo bar or kits—with or without shock mounts. Find one that suits your needs for quick, precise, and repeatable ways to switch between different mic technique setups.

The most important rule of all, listen to your ears and, specifically with stereo pair mic'ing: Take your time. Do not rush this and listen carefully for phasing. Get experimental and don't forget to have fun.

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