Theoretical and Practical Considerations in Compression Hearing Aids

Most clinicians are aware of the excellent summary on the topic of compression written by noted researchers such as Braida et al (1979), Walker and Dillon (1982), and Dillon (1988). A reasonable question is: why this paper? The fact is that over the last 10 years there has been a dramatic increase in the number of scientific papers and clinical reports on the use of compression in hearing aids. The present attitude towards compression hearing aids is certainly more positive than that expressed in previous reports. This change in interest from linear amplification with peak clipping to an alternative output limiting approach is also reflected in the increasing number of hearing aid manufacturers incorporating compression circuitry in their hearing aid design. While hearing aids using compression as output limiting offers some advantages over hearing aids using peak clipping, the use of compression is not without controversies. Some of the theoretical arguments made in favor of a particular compression approach may have practical limitations. In addition, many benefits reported with one form of compression may not be exclusive of that compression approach. This paper will review the electroacoustic specifications for compression hearing aids, and examine some theoretical and practical advantages of different compression approaches. In addition, considerations will be given to how some of the theoretical issues may require clinicians to re-evaluate their current practice of fitting such devices. Perhaps a better understanding of these issues may facilitate one's choice for a particular output limiting approach for a hearing aid wearer.