The CRC for Cochlear Implant and Hearing Aid Innovations at NAL has cooperated with Telstra and Polaris Pty Ltd to produce a sophisticated device that improves intelligibility, listening comfort, and the level of protection provided to call-centre workers. Unlike existing analog sound limiters, the CRC solution uses digital signal processing to tailor the sounds present at the eardrum.  The commercial version of the device is called the Sound Shield^TM (see below).  Sounds are altered in a variety of ways:

Automatic comfort control. The signal level of telephone calls varies considerably. The Sound Shield monitors the incoming call, the operator’s voice, and signaling tones (dial tones etc) to consistently present sounds at a comfortable level. The device compensates for the variation in characteristics between different types of headsets that are used by operators.

Hearing protection. The incoming call is monitored to detect high intensity sounds. The Sound Shield then rapidly reduces the amplification so that even very brief sounds do not cause momentary discomfort. A fast-acting sound level limiter and a very fast high-level transient sound suppressor limit the impact of brief "spikes" (clicks and pops etc.) without significantly degrading speech clarity or quality.

Shriek rejection. The most innovative feature of the Sound Shield is its ability to recognise and eliminate shrieks. Shrieks are typically high-pitched piercing sounds. A dual-band "shriek rejecter" tracks and simultaneously suppresses up to two of these sounds while preserving the remaining sound spectrum. Suppression occurs so quickly that the distressing and potentially damaging shriek is turned into a barely audible brief sound pip. This feature enables the operator to continue conversing, even if the fault in the phone network persists.

These solutions use several principles of operation that the CRC had devised in its quest to improve the effectiveness of hearing aids. Some additional operating principles were devised specifically to guard against acoustic shock.

The Sound Shield is compatible with most headsets and telephone systems. 

Field testing

Telstra has constructed and trialled a number of prototype devices that incorporated the signal processing software devised by the CRC. Tests were carried out in a call-centre that had previously experienced a high incidence of shrieks. Operators reported that they preferred the sound quality, clarity and comfort of the prototypes, and felt increased confidence that the device protected them from harmful sounds. (The high level of protection provided by the device is easily demonstrated to operators, and developing this confidence by the operators may be an important element in providing a comprehensive solution to the problem.)

Manufacturing and Licensing

The CRC for Cochlear Implant and Hearing Innovations have granted Telstra an exclusive licence for exploitation of the software devised by the CRC. Telstra have organised the manufacture of over 1000 Intelligent Limiters for placement within its call centres. Telstra have also sub-licensed the software and their hardware developments to Polaris Pty Ltd.  Polaris have re-engineered the product to better suit a wide range of call centres and have released the product as the Sound Shield^TM.

                     The Sound Shield won an Award for Technology Transfer at the CRC Association Conference on 22 May 2002.

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