Tech Notes - A Guide to Recording in Stereo

A Guide to Recording in Stereo

QUICK LINKS: How Stereo Works | Diaphragms | Coincident Pairs | Spaced Pairs | Microphone Table

The following article is a collection of stereo recording techniques gathered from internet and text book sources. It covers the most common stereo recording methods in a concise and easy to use guide for the home recording engineer.

Recording in stereo gives the listener a better sense of:
- The recording space (natural reverberation, echo).
- Relative positioning of each instrument to one another.
- Distance from the audience to the performers.
- What it would be like to be in the room with live performers.

sE Electronics makes a variety of condenser microphones, both large and small diaphragm, ideal for stereo recording techniques. Please refer to our table of microphones at the end of this article to check prices, applications, diaphragm sizes, and to find the sound you're looking for.

Small diaphragm microphones are excellent room mics as they are generally voiced to capture the entire sound spectrum evenly. Smaller diaphragms may lack the warmth of their large diaphragm counterparts, but they have a quicker transient response. Therefore, they can capture cymbals, snare drums, strings, and other “fast attack ” sounds more accurately.

In a coincident-pair, the diaphragms of two microphones are placed as close together as possible and angled differently in order to capture a stereo image. Coincident-pair is the more accurate of the two techniques mentioned in this article. Since the microphones pick up sound at the same location, there is more phase accuracy than a spaced configuration, though less ambience is recorded. Because the microphones are located on the same plane, imaging is more directional, making it easier to detect phantom images in the stereo field upon playback. Of course, make sure you pan each track appropriately on playback so you hear the stereo image!

X/Y
The most common form of the coincident-pair techniques is the X/Y combination. The angle between the microphone grills can vary from 90 to 120 degrees, facing towards the sound source. Cardioid microphones are the best choice for this setup, as the stereo images will appear more dramatic and focused. Be sure to pan each track to so that you can hear the imaging. The X/Y array always uses two microphones of the same make and model to ensure a consistent stereo image. sE has specially matched stereo pairs of the sE1a and sE3, ideal for this style of miking. We offer a free 7-day loan service on all sE mics. If you are interested in trying some out, please contact us!

sE3 Pair arranged in an X/Y Pattern	The X/Y Pattern

Blumlein
The original X/Y, this second style of coincident-pair microphone techniques is called the Blumlein Array. It was created by Alan Blumlein in the 1930’s after he was disappointed by the sound quality of a monophonic movie he attended. The Blumlein Array has since become a staple in stereo recording. Specific to this style of recording is the use of microphones with figure of eight polar patterns. Try using a pair of sE R1 Ribbon, Z3300A, Z5600A II, or Titan microphones for this setup. This tried and true method places the mics on the same vertical axis at 90 degree angles to each other, the center angle facing the middle of the sound source. The balance of the two figure of eight patterns allows for an even balance of sound between the microphones. The additional pick-up of sound from the rear of the microphones creates extra natural room reverberation, and thus a more spacious sound. For more information on Alan Blumlein and his contributions as an early pioneer towards all things audio, including the development of stereo, visit this website.

The Blumlein Array with two R1 Ribbon Microphones	Polar pattern of the Blumlein Array

M-S
The Mid-Side or "M-S" technique, uses two microphones; one cardioid and one figure of eight. The major advantage of M-S recording is the ability to have a left, right, and center image while using only two microphones. The cardioid microphone is positioned facing the sound source while the figure 8 mic is placed perpendicular, creating a "T" shaped pattern. To capture both sides of the figure of eight microphone, two identical tracks must be recorded. This can be done either by recording the same input into two seperate tracks or by duplicating the track once it is recorded. Using a polarity switch ( ) on your mixer or computer software, one of the tracks must be placed out of phase/polarity with the other, isolating each side on playback. Pan the in phase track to one side and the reversed phase track to the other. Note: Since these tracks are 180 degrees out of phase, panning them to the same position should yield no sound! Center the cardioid track between the figure of eight tracks. By adjusting the two side tracks with the middle, the engineer will have excellent control over the amount of stereo imaging in the recording. As an alternative, you may use an M-S encoder which combines the signals and allows you to adjust the balance between them.

Our example below utilizes two Z3300A microphones. Although using identical microphones will give you a more consistent overall sound, you may wish to experiment with different mic combinations.

Two Z3300A’s in an M-S configuration Note the 90 degree rotation of the bottom microphone	The M-S Polar Pattern

The Spaced Pair microphone technique is by nature more difficult to use due to potential phase problems. However, when used properly, it can yield a more spacious recording. There are a wide variety of spaced pair techniques, angles, distances, and mic choices.

Potential Problems:
Before recording with a spaced pair, it is important that the engineer understand the potential phasing problems that may arise. Phasing often occurs when two microphones, recording simultaneously, capture different portions of the wavelength of the original sound source. Upon playback, they are perceived slightly out of time with each other by the listener, causing most notably a loss of bass and “smear” of higher frequencies. This will create either constructive or destructive interference in the recording, resulting in volume and delay issues.

The 3:1 Rule To avoid phase cancellation when stereo miking, always follow the 3:1 Rule. Make sure the distance between your mics is at least three times further than the distance between the mics and the source. The graphic to the left demonstrates an example of the 3:1 Rule in use. By placing the mics spaced above the hammers, a bright percussive sound is captured without phasing issues. This setup yields a great stereo mix, with bass notes on the left mic, and treble notes on the right.

ORTF, NOS, Faulkner, and The Stereo 180 Technique
These set-ups are all variations of the spaced and near-coincident pair. Their designs are very similar, with the major differences relating to the distance between the mics and the relative angles they are positioned at. The ORTF, or “Office de Radio-Television Diffusion Française” (designed by the French Broadcasting Organization) uses two cardioid microphones angled at 55 degrees away from center, spaced at 17 centimeters. This set-up is designed to approximate the human head and the effect of sound hitting the outer-ear. The NOS Array (Nederlandsch Omroep Stichting, a Dutch broadcasting company design) uses two cardioids splayed at 45 degrees off center with a spacing of 30 centimeters between. The Faulkner Array, designed by Tony Faulkner in the late 1970’s, uses two figure of eight microphones, facing parallel towards the sound source and spaced at 20 centimeters. The Stereo 180 technique is the most precise of the near-coincedent arrays. With a distance of 4.6 centimeters between capsules, two hypercardioid microphones are splayed 67.5 degrees off center.

In Conclusion

sE Electronics Microphone Table:

Click on the microphone model for a product sheet with specs, applications and more.

References:
http://www.tape.com/cgi-bin/SoftCart.exe/Bartlett_Articles/stereo_microphone_techniques.html?L+cassette+nqna2923+995498793
http://www.wesdooley.com/pdf/technique.pdf
http://homerecording.about.com/od/microphones101/a/mic_types.htm
http://www.sweetwater.com/insync/word.php?find=JecklinDisc
http://en.wikipedia.org/wiki/Dummy_head_recording
http://en.wikipedia.org/wiki/Image:Blumlein_Pair.svg
http://emusician.com/mag/Mid-Side-Miking-Fig.-1.gif
http://en.wikipedia.org/wiki/Image:ORTF-Stereo.png
http://m-pulse.m-audio.com/articles/march2003/images/xy.jpg
Eargle, John. The Microphone Book, Second Edition, Copyright 2004.
Runstein, Huber. Modern Recording Techniques, Second Edition. Copyright 1986
Runstein, Huber. Modern Recording Techniques, Sixth Edition. Copyright 2005

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