Single channel, digital, direct recording to disc will be used for the microphone signal. Digital audio tape recorder safety backup will be made of microphone channel at all times. Second channel recording direct to disc and/or digital audio tape recording of the Laryngograph signal will be made as required.
The mechanism for direct digital recording to disc will be by use of the OROS AU21 board for single channel or an OROS AU22 for two-channel recordings on the SESAM workstation with EUROPEC software. The sampling rate will be 20kHz, and the standard OROS digital filtering is used with an over-sampling factor of 4. The nominal resolution of this system is 16 bits. Care should be taken to ensure that OROS board is placed in a slot in SESAM which minimises PC electrical interference.
The ``standard'' analogue filter on the OROS board is a 20kHz low-pass filter with 0.3 dB ripple in the passband, 160 dB/octave slope and 80dB rejection. This is followed by a digital filter implemented on the TMS320C25 having the -3dB point at 8kHz. Any DC offset is automatically removed by the OROS/EUROPEC software and the gain of the line input will be set within EUROPEC on a ``per speaker'' basis.
The safety backup (and second sensor recordings if an OROS AU22 is not used) will be made on a digital audio tape system such as the SONY Video PCM or DAT systems, having a specification with regard to bandwidth, signal-to-noise ratio and wow and flutter in excess of that of the OROS AU21 board. The recorder shall be left recording for the WHOLE of a session and not be stopped or rewound at all during the session. This removes the chance of over-recording wanted portions, reduces the operator effort will allow later analysis of a number of features not captured on the direct to disc recordings, such as number of retakes, motivation level of subject, coughs etc.