A single B&K half inch pressure microphone number 4155 will be used connected to a 2230 level meter, used as a microphone amplifier. If a recording site proposes to use another microphone or preamplifier the alternative choice of equipment should be ratified by other members of the project. IES has suggested a 4165 microphone, 2660 pre-amp and 2636 amplifier. Bochum University recommend the ADG C-414 microphone in omnidirectional mode connected to the John Hardy M-1 mic preamp.
The audio output of the level meter will be connected to both the line input of the OROS AU21 board and the left channel of the digital audio safety backup recorder. The method of splitting the signal will be made in such a way to ensure no degradation of the audio signal particularly in terms of loading, balanced/unbalanced connections and hum loops. Bochum University recommend the Brooke Siren Sytems microphone splitter.
The microphone will be positioned for 90 degree incidence, 50cm from lips 15 degrees off axis. (TNO configuration)
Tests by NPL have shown that this distance is acceptable in terms of speech signal to ambient/monitor noise.
The microphone position relative to the head/lips will be set and maintained by a headrest (or the not so consistent method of requesting the subject to maintain head position).