Question
Can you tell me more about the compression strategy used in Syncro? How do I make it work best for the patient?
Answer
A key component of the Voice Priority Processing system in Oticon Syncro is our new approach to compression, Voice Aligned Compression (VAC). The VAC approach falls within the family of Wide Dynamic Range Compression (WDRC). WDRC is essentially the standard for fitting sensorineural hearing loss.
Within the family of WDRC, there are options on some rather important dimensions. Most WDRC applications in digital hearing aids use "linear" compression, meaning a fixed compression ratio is used once the signal is between the primary kneepoint (usually 45 or 50 dB SPL) and the output limit. However, in more sophisticated applications, the kneepoint of compression and the compression ratio can be implemented in a more strategic manner. In Syncro, the eight channel VAC approach uses much lower primary kneepoints (varying between 30 and 40 dB, depending on frequency region, amount of hearing loss and Identity setting) and curvilinear compression, with higher gain and compression ratios for softer speech input levels. For higher input levels, the compression ratios decrease, with significantly lower gain applied. This compression model is based on recent data out of Northeastern University (Buus & Florentine, 2001) and represents a more natural solution to restoring the audibility and loudness perception lost with sensorineural hearing loss.
We have two fundamental goals with our new VAC approach:
- To provide excellent gain for speech in the soft to moderate range, where users with SNHL need audibility help for soft speech sounds and can typically handle significant compression without the loss of signal integrity.
- To provide a more linear response in the moderate to loud range. We believe that near linearity allows the best access to speech information when background noise is present (as is common in moderate to loud environments).
The initial patient reaction to our approach to compression has been very positive. Reports from new and experienced hearing aid users emphasized naturalness and sound quality as key qualities appreciated using the VAC. Audibility for softer speech sounds was noticed and appreciated, while acceptance and comfort in louder, more demanding situations has not been sacrificed.
Donald J. Schum, Ph.D./CCC-A
Vice President,
Audiology & Professional Relations
Oticon, New Jersey
