The Independent Hearing Aid Fitting Forum (IHAFF) Protocol

The Independent Hearing Aid Fitting Forum (IHAFF) protocol was developed between 1993 and 1994 during numerous weekend meetings in Denver, Tampa, Anaheim and Chicago. The protocol was the brainchild of Dennis Van Vliet and Michael Marion, who were frustrated by the gap between the ever-evolving technology and the tools available for selecting, fitting and verifying the performance of hearing aids. As clinicians, they were concerned that there was a general lack of knowledge on how to appropriately determine if their patient was a better candidate for wide dynamic range compression, compression limiting, or compression in which the compressor is activated at an intermediate level. Further, they were concerned about the decisions that clinicians were being asked to make everyday which did not need to be made just a few years ago. For example, how to appropriately adjust the compression ratio (CR), compression kneepoint (KP), release time or output in one or more channels. In addition, they were concerned that the present prescriptive formulas, which are appropriate when fitting linear hearing aids, are not appropriate when fitting hearing aids with nonlinear signal processing. Finally, Dennis and Michael did not see any activity when attending professional meetings or reading professional journals which gave them any hope that relief for their concerns was forthcoming. Due to these concerns, Michael and Dennis believed that it was necessary to gather colleagues together who might be able to develop a protocol to help clinicians better serve their patients when dispensing hearing aids containing both linear and nonlinear signal processing. The members of the IHAFF committee were Lucille Beck, Ruth Bentler, Robyn Cox, David Fabry, Gail Gudmundsen, David Hawkins, Mead Killion, Michael Marion, Gus Mueller, Larry Revit, Michael Valente and Dennis Van Vliet. Margo Skinner was an early member of the committee but had to leave because of other commitments. As the reader can imagine, the discussions at these meetings were stimulating, challenging, intriguing, heated and controversial. Numerous fitting and verification strategies were discussed and discarded for a variety of reasons. For example, early discussions centered around referencing all measurements (threshold and loudness judgments) to dB SPL near the eardrum (i.e., SPL-O-GRAM). However, this idea was dropped because equipment was not available to perform these tasks in a clinically efficient manner at the time of the discussions. As the reader knows, such equipment is now available (i.e., the Madsen Auracle, Etymonic Design's AudioScan, Starkey Pro-Connect, ReSound's Real Ear Loudness Mapping (RELM) and Frye real ear analyzers). Discussions were also especially prolonged around the issue of “predicting” loudness judgments from threshold as opposed to individual measurement of loudness judgments. The final IHAFF protocol requires individual measurement of loudness scaling. Important considerations such as counseling, fine-tuning, aural rehabilitation, assistive listening devices, directional microphones, remote controls or digital volume controls were discussed, but it was decided not to include these issues in the final document. The result of those meetings, phone calls, faxes and e-mail messages is the IHAFF protocol. The primary goal of the IHAFF protocol is to “normalize” the loudness experiences of the hearing-impaired patient. Specifically, the goals of the IHAFF protocol are: Sounds judged as “soft” by a normal listener should be audible and judged as “soft” by a hearing-impaired listener who is wearing hearing aids. Sounds judged as “comfortable” by a normal listener should be judged as “comfortable” by a hearing-impaired listener who is wearing hearing aids. Sounds judged as “loud” by a normal listener should be judged as “loud”, but not “uncomfortably loud” by a hearing-impaired listener who is wearing hearing aids. Also, to prevent amplified sounds from exceeding the user's uncomfortable loudness level (LDL). Typically for a cochlear-impaired listener, the use of compression and more than one processing channel will be needed to reach these goals. That is, less gain would be supplied at the higher input levels (compression) if the patient exhibits loudness recruitment, and greater compression might well be needed in the high frequency region where typically the dynamic range between threshold and UCL is reduced in comparison to the dynamic range in the low frequency region. This issue of Trends in Amplification is dedicated to providing the reader with a better knowledge of how to implement the IHAFF protocol. The manuscript is divided into two sections. The first section describes, in detail, how to operate the software that has been developed to assist the user to implement the IHAFF protocol. The second section illustrates the implementation of the IHAFF protocol by “walking through” the entire process with one of our patients.