Gefell M300 pencil begins with a 21mm gold evaporated Mylar diaphragm assembly with a temperature-constant ceramic housing. This technology was borrowed from Gefell's Test & Measurement division whereby when testing rockets for aerospace; it was found that temperature shift would cause metal expansion and performance shift. Ceramic components are proven to provide a more stable and uniform platform when the microphone is subjected to changing environmental conditions.

To reduce self-noise, an innovative DC to DC optical converter eliminates spurious electrical currents and noise typical of 48V phantom powering, thus providing a pure DC voltage to the capsule. This results in the quietest operation levels while delivering a full 80-volt plate voltage, for an unprecedented ed 147dB signal handling without the use of an input attenuation pad. This makes the M300 an ideal candidate for the demands of today's advanced analogue and digital recording formats.

Unlike other companies that employ 'golden ears' alone to stereo match the microphones, each Gefell M300 set is stereo matched following a series of stringent tests. To begin, the microphones are tested in a 3-dimensional anechoic chamber with suspended floor. The microphones are positioned on a 'robot' that records both on-axis response for bandwidth and linearity and then 180º off-axis response to measure the microphone's performance and phase response within the acoustic field. Daily temperature and barometric pressure is tabulated and microphones are batched within set criteria to ensure that a stereo set truly performs as a frequency, amplitude and phase matched set. Each microphone is shipped with its own serialized on-axis and 180º off-axis frequency response curve providing the user with real, tangible test criteria. The microphones then pass an aural auditioning in a separate listening room before being packaged.

The M300 Stereo Set is configurable for both XY or ORTF formats. Because the microphones are tested for both on-axis and 180° off-axis response, one can be sure that the microphones will perform as a true stereo set, capturing the same frequency response, the same level and of course, the same diffuse field response.

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