Evaluation of the Hearing Threshold in accordance to ISO 4869-1 with and without hearing protection in a synthetic sound-field.

DEvaluation of the hearing threshold in a diffuse sound-field according to ISO 4869-1. Automation of the complete test routine for the derivation of the hearing threshold level of a test person. Application of either continuos tone or pulse tone method. User friendly PC-software for test routine and calibration of sound-field (Windows-software with graphical user interface).

The concept of the Nor-838 is based on the combination of modern computer technology with nowadays high performance digital audio-technology. Digital communication and data exchange between PC and digital audio front-end delivers unaffected pure audio signals with the comfort of a graphical user interface. To connect the PC to the digital audio frontend a PCI-card is used.

The digital audio front-end contains the micro-controller as a base-unit for interfacing to the PC, two sets of dual channel DA-converter cards (Nor-838 1) and a input for the hand switch. The unit uses a standard 19, 3 unit high case with a sturdy aluminium diecast frame. Due to the AES/EBU digital audio interface and the RS232 controller interface all connections to the PC may be as long as needed.

Performance data Nor-838-1:

• Audio-Interface: AES/EBU symmetrical
• Audio out: +20 dBu symmetrical, XLR connectors
• Signal processing: 1 Motorola DSP56009 for one card used for levelling, noise shap-ing, and ramp generation. Controlled by the system µC
• Sampling rates: 32 kHz, 44.1 kHz, 48 kHz
• Data format: 24 bit linear audio quantisation
• DA-Converter: 20 bit R2R-converters, with selected linearity < 0.001 % THD
• Signal to noise: > 110 dB full scale
• Level adaptation: -20 dB output attenuation relays to maintain ultra low noise and highest linearity even at very low levels.