The problem for a hearing-impaired person, is far more complex than simple amplification of sound. Most people with hearing loss - particularly older adults - are able to hear some sound frequencies better than others. Across the board amplification just makes garbled sound louder, some hearing aids contain some kind of signal-depending gain reduction, such as peak clipping and input or output compression; however, these simple ways to introduce non-linearities in hearing aids do not solve this problem. They only limit the discomfort of using a hearing aid.
Hearing losses can be divided into classes, with several different degrees of hearing losses in each class. Since more than one type of hearing loss often are seen together, this makes each hearing loss truly individual. Also, the fact that hearing-impaired persons prefer different types of sound presents obvious problems for the manufacturer and the dispenser of such devices. It becomes evident that the required signal processing should be flexible and powerful. It appears that the optimal solution would be to have a general device that could be programmed to fit all sorts of hearing losses.
We therefore propose to develop two-purpose digital signal processors for use in hearing aids. We will use the name General Hearing-aid Processor (CHP) for both of them, since they will both be capable of meeting a broad category of hearing-compensation demands. These processors will truly enable the dispenser of the product to fit the aid optimally for each individual user. The GHP will be flexible enough so that it can be adapted to suit future needs. It will also be able of solving some problems in hearing-aid design that cannot be solved with present analog techniques. Such problems include:
- The exact fitting of amplification to the hearing loss. The filters contained in GHP will be programmable, and therefore flexible in their characteristics.
- For compensating different hearing losses in different frequency regions, a high degree of flexibility in gain and compression methods is required. Multi-band signal processing will allow optimal fit for each user.
- Time constants and operating levels of AGC circuits are more or less fixed in analog hearing aids.They will be individually fitted with the GHP.
In addition, the GHP will allow an efficient individual compensation of hearing losses in a way that will raise the listening comfort and life quality of the hearing impaired. Furthermore, a GHP can serve as a development tool in the service of discovering new ways to help the hearing impaired and as a tool for the development of new standards in the hearing-aid field, let aside the standards that itself is going to set as the most advanced device to date.