Microphone Techniques for Stereo Recording
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 Ribbon Microphones
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 microphones in an M-S configuration.
Note the 90 degree rotation of the bottom microphone
Spaced Pair Techniques
Spaced benefits:
- Room ambience is enhanced
- Better low-frequency response
- Stereo images are wider
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 below 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.
