Studio Stereo Microphone Approaches: A Look at the Leading Four Methods Used
In the world of audio recording, using multiple microphones has become a popular approach to add depth and dimension to recordings, moving beyond the traditional single mic method. Today, several common stereo microphone techniques are used in recording studios to capture the essence of sound and recreate a realistic stereo image.
One such technique is the X/Y Technique, which employs two directional microphones placed with their capsules as close as possible and angled typically at 90° to 135°. This setup produces stereo imaging mainly based on level differences between left and right channels, with minimal phase issues due to the proximity of the capsules.
The ORTF Technique, named after the French broadcasting organization, uses two cardioid microphones spaced about 17 cm apart at a 110° angle, mimicking the spacing and angle of human ears. This method captures both level differences and time-of-arrival differences, yielding a natural stereo image.
The A/B Technique, also known as the spaced pair, uses two omnidirectional microphones spaced apart (often 50 cm or more). This method relies primarily on time delay differences between the channels to create stereo width, producing a wide but sometimes less focused image.
The Mid-Side (M/S) Technique combines one forward-facing cardioid (Mid) microphone with one figure-8 (Side) microphone positioned sideways. The two signals are recorded separately and decoded later into left and right channels, allowing stereo image control by adjusting the balance of Mid and Side signals and maintaining mono compatibility.
Another variation of the XY Technique is the Blumlein mic technique, which uses two figure-of-eight mics and is best used in great sounding live rooms. This technique creates a detailed stereo image based on both level and phase differences, capturing a very natural spatial impression.
The Decca Tree mic technique, a variation of the AB Technique, uses a third omnidirectional mic in the middle of the other two mics to fix the "hole in the middle" issue.
Binaural recording, while not mainstream, is meant to be listened to on a pair of headphones for an accurate representation of the sound at the recording stage. Binaural recording uses a model of a human head with a pair of microphones placed inside the ear canals, also known as 'Dummy head' recording.
These techniques create stereo images through different combinations of inter-channel time delays, amplitude/level differences, and polar patterns that provide spatial cues to the listener's brain, simulating a three-dimensional sound field. For example, the Haas (Precedence) effect states that a small delay (under ~40 ms) between channels makes the ear perceive the first arriving sound as the source direction, which is exploited in some stereo techniques to enhance localization.
In summary, stereo microphone techniques differ primarily in microphone placement and orientation to capture spatial cues that recreate the stereo image, aiding localization and depth perception in the recorded audio. The choice of technique depends on the source, desired stereo width, room acoustics, and mono compatibility considerations.
Advanced stereo imaging in mixing can involve Mid/Side processing to independently adjust center and side sound elements, and stereo widening, though used cautiously to avoid phase and mono issues.
References: [1] [Link to reference 1] [2] [Link to reference 2] [3] [Link to reference 3] [4] [Link to reference 4]
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