Calibration

The recording chain will be calibrated in two ways:

1. A B&K 1kHz 4230 calibrator is placed over the microphone.
2. The injection of a 4:7 Mark-Space ratio square wave of 20Hz and 100 Millivolts pk-pk. electrical signal into the microphone body. This is achieved by the use of:
   1. a signal generator (the circuit of which can be obtained from UCL);
   2. a B&K Input Adaptor, JJ 2614, which replaces the microphone capsule;
   3. a capacitor of a value equal to that of the capsule element replacing the 1nF capacitor in the B&K adaptor.

A recording of both calibrator signals shall be made every 20 sessions, providing confirmation of gain calibration, and recording path frequency response, phase response and noise figure. The length of recording of each calibrator shall be 10 seconds plus 10 seconds of no signal condition. It would be sensible to check the signal-to-noise ratio using these files at the site to confirm the correct working of the system.

The Laryngograph channel shall also be calibrated, using the UCL 4-7 mark-to-space ratio rectangular wave calibrator.