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continuously variable pattern selectionCore Sound TetraMic

Multi-Pattern Condenser Stereo Microphone

The TetraMic is an ambisonic soundfield microphone, capable of mono, single-point stereo, and surround-sound recording.

This unusual microphone has four small-diaphragm condenser capsules mounted in a tetrahedral arrangement; their output can be post-processed to create any mono pattern you can name, in infinite variations from Omni to Figure-of-8, or stereo patterns such as Blumlein, Mid-Side, XY Stereo, and binaural, or surround formats such as 5.1, 7.1, and 10.1.

According to Core Sound, “The apparent orientation can be rotated, tilted, tumbled or zoomed at will.”

The four electret condenser capsules measure 12mm in diameter. Each is rated at 19dBA of self-noise, with a max SPL of 135dB. Raw frequency response is 40Hz - 18,500Hz.

However, after the signal from the four capsules is combined and processed, these raw specifications no longer apply. The decoded audio file will have wider and flatter frequency response than the raw capsules, and could have lower self-noise as well.

One of the ways the TetraMic is distinguished from its competition is the care with which capsules are selected and calibrated. Large quantities of 12mm electret condenser capsules are tested, sorted, and matched for sensitivity, frequency response, and directivity of the native cardioid pickup pattern, as well as other specifications. Once a set of four suitably-matched capsules is identified, the set is mounted into a tetrahedral formation and extensively tested again. Individual calibration and correction files are supplied with each microphone, to be used by downstream decoder software.

Audio processing (decoding) can be done in realtime for monitoring purposes, via VST plugins provided by Core Sound. The company also provides a standalone audio decoder application. (See the company website for compatibility notes.)

Therefore, it is possible to use a single 4-channel recording from the TetraMic to produce any variety of single-point stereo mix, then to augment that stereo mix with virtual directional spot mics extracted from the same recording.

Given the special abilities of this tiny microphone, field use requires some additional hardware. Ideally, the mic needs four preamp channels that have been gain-matched to 0.1dB — although the raw audio channels can be gain-matched in post-production prior to decoding if necessary. Further, the mic needs 4.5–6VDC of power, which can be derived from a phantom power supply given appropriate adapter hardware. See the Core Sound website for a detailed discussion of products that meet these needs.

ProSoundWeb, 2009

Overall, the sound quality of the TetraMic was excellent. Image focus and placement sounded natural. Localization was precise, yet with plenty of ambient detail.

I heard clean, clear sound, plenty of low end and depth, and no audible distortion. Movement of images across the stereo stage was very smooth.

For more information on ambisonic soundfield recording with the TetraMic, see the excellent ProSoundWeb and Ambisonics Info articles linked from the sidebar.

Permalink: Core Sound TetraMic

The mic was released in 2006.


Pickup Patterns Pads & Filters
Cardioid (7 mV/Pa; 40 - 18,500 Hz)
Capsule Dimensions Impedance SPL/Noise
Capsule diameter: 12mm
n/a Max SPL: 135 dB
Self-noise: 19.0 dB(A)
Weight Length Max Diameter Interface(s)
n/a 133mm (5.24'') n/a
    Power Specifications
    • Requires phantom power
    • Phantom voltage: 4.5–6v

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