Forum Proceedings

Technology Area

Clinicians, researchers and manufacturers identified FM Systems as an area that would benefit from new and innovative technology. They believed that improvement in FM system technology would help in developing better assistive hearing products that would meet significant end-user needs, and create significant business opportunities. FM based ALS include personal FM systems, large area FM systems, and FM sound-field classroom systems.

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Market Need

Hearing aids provide user-customized processing of sound signals picked up by the hearing aid's microphones, telecoil or FM receiver (either in-built or an accessory to the hearing aid). Modern hearing aids use signal processing to make speech more understandable for hearing impaired persons (e.g., algorithms to remove certain undesirable sounds, compression or amplification of the certain frequency sound signal, etc.).

Assistive Listening Systems (ALS) are typically used to amplify selected sound signals, to overcome background noises, enhance sound in large public venues or to improve one-to-one conversations. An ALS reduces the acoustical space between a remote sound source and the listener. Many ALS are currently available, including (but not limited to) infrared systems, FM systems, and inductive loop systems. Each of these ALS transmits a relatively noise-free signal from a remote sound source directly to the receivers of one or more users wearing an appropriate receiver.

ALS can be used in combination with hearing aids, or by themselves. In many cases, use of an ALS in conjunction with a hearing aid provides the user with the optimal sound clarity and comprehension. ALS also includes such devices as amplified doorbells, phones and alarm clocks.

Binaural hearing aids currently refers to the use of hearing aids in both ears where each hearing aid processes its sound signal independently. The user's residual ability to process binaural sound cues (e.g. head shadow, phase and timing) may or may not be significant. A communication link between these hearing aids would permit true binaural processing by the hearing aids themselves. In order to be accepted, this communication link should be wireless (Kompis, Feuz, Valentini, & Pelizzone, 2000)

It is estimated that there are more than 20 million people in the U.S. who experience some form of hearing loss.^* Hearing aids or assistive listening systems can aid about ninety to ninety-five percent of this population. A large majority of these people (approximately eighty-percent) have chosen not to make use of available technologies. This leaves more than 16 million people with substantially correctable hearing loss who are not seeking treatment, or addressing their hearing loss by other means.

According to the 1990‑91 National Health Survey study, 3.6 million people who identified themselves as having hearing problems used hearing aids. ^* Use of hearing aids is highest among the 18 years of age and older groups whose hearing loss became significant after the age of 19. In 1999, hearing aid sales in the United States were estimated at 1.9 million units.^** The hearing aid industry accounted for $1 billion in revenue in 1993 and is currently estimated at $1.43 billion (5.2% compound growth rate; Frost & Sullivan, 1994).

Assistive Listening Systems have general market potential beyond the needs of people with hearing impairments. For the hearing impairment market, an Advance Data Reports from the National Center for Health Statistics reported that in the U.S., approximately 874,000 persons who are "hard of hearing" use amplified telephones, ALS, and other hearing technologies (not including hearing aids; National Center for Health Statistics, 1997). This figure represents less than 5% of the population who could benefit from such technology. ALS are used as private, noise free communication channels. For example, IR or FM listening systems are already common in schools and museums. The potential ALS market is broader than the hearing aid market because of general market ALS applications for the non-hearing impaired (e.g. guided tours through a museum exhibit) and for persons with non-hearing disabilities (e.g. blindness).

The Americans with Disabilities Act (ADA) and the Telecommunications Act have increased the popularity and availability of assistive technologies for employment, education, and access to buildings, transportation and telecommunications. The ADA requires that any business (auditoriums, theaters, etc) with 50 or more fixed seats in an assembly area must make ALS available for at least 4% of the seating capacity (Bakke, Levitt, Ross, & Erickson, 1999).  In practice, many ALS are "provided upon request," rather than being permanently installed. However, an ALS that is not permanently installed may or may not be available to the user in a timely fashion. In addition, ALS equipment may not be installed or maintained (e.g., batteries uncharged, incomplete systems) properly.

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Basis for Discussion

Assistive Listening Systems bring a remote, essentially noise-free sound signal directly to the hearing impaired listener across the intervening reverberant and noise filled acoustic space. ALS extend the hearing range of these individuals.

Directional hearing aids attenuate peripheral sounds and focus on sounds directly in front of the listener. These devices provide better understanding of speech in noise when the speaker is close by but provide little benefit when the speaker is distant. Used in conjunction with hearing aids, wearable and hand-held "directional beam-forming microphone arrays" further improve the perception of close by speakers.

ALS are typically classified by the technology that provides the wireless link between a distant transmitter and body worn receiver. The three most common technologies use infrared light, an electromagnetic field and radio waves to establish this link.

This discussion focuses on systems using FM (frequency modulated) radio waves. Some hearing aids already use in-built or external FM receivers that can be coupled to ALS as well as hand-held and wearable directional microphones (AVR Sonovation, 2000; Phonak, 2000). An FM communication link between hearing aids would support advanced binaural processing. Small area ALS might use short-range FM remote microphones.

Improvements to and application extensions of FM technology will provide important benefits for end-users and significant business opportunities to manufacturers.

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Current Technology

The following discussion relates primarily to FM personal systems, large area systems and sound field systems. The sound input of a personal or large area FM ALS is frequency modulated and transmitted. Transmissions typically use non-overlapping 50 kHz bands (referred to as "narrow band transmission"), or 150 kHz / 200 kHz bands (referred to as "broad band transmission") in two portions of the frequency spectrum - 72 MHz to 75 MHz and 216 MHz to 217 MHz. Federal Communication Commission regulations limit the permitted maximum power of the transmitted signal. The typical range (transmitter to receiver) for FM ALS is approximately 300 to 500 feet (at 72 MHz to 75 MHz). Range can be increased by using a larger antenna or by transmitting at higher frequencies (216 MHz to 217 MHz).

The portion of the frequency spectrum employed by FM ALS is non-exclusive and unlicensed. These systems are therefore subject to interference from other radio transmissions (e.g. pagers, emergency vehicles, etc.). Some FM ALS can transmit and receive in a number of frequency bands (as many as 50 narrow bands or 10 wide bands). Because these bands are non-overlapping, simultaneous, non-interfering communication can take place within the same environment. If an extraneous radio signal causes interference, the transmission frequency of the FM ALS can be changed (e.g. to the frequency of another narrow band). The listener then manually changes their receiver to match this frequency.

Large Area FM Assistive Listening Systems

A large area FM ALS is most commonly used for single input, multiple listener environments such as conference and classrooms, churches, nursing homes, theaters, and courtrooms. The most common input device is a single microphone, but multiple microphone positions and alternative sound sources such as tape machines and audio‑mixing equipment may also be interfaced to the system.

Many large area FM ALSs can provide a range of input preprocessing options. It is unclear whether such preprocessing, coupled with the customized signal processing provided by each listeners' hearing aid will generally improve signal clarity or speech comprehension. The dynamic range of input signals can be quite large and some form of input compression will often be necessary to avoid saturating the output signal while still maintaining audibility at low input levels.

Various options are available by which to interface the FM receiver to the listener's hearing aid. Hearing aids with T-coils, neck-loops or silhouette inductors can be plugged into the FM receiver. For hearing aids lacking a T-coil, earphones can be employed. Earphones probably won't comfortably fit over a BTE (behind-the-ear) hearing aid. Some hearing aids will also accept direct audio inputs (DAI).

FM ALS portable receivers can use rechargeable batteries (typically 6-10 hours of continuous use between charges) or disposable batteries (typically 18-70 hours between replacement). The systems require administration -batteries must be charged or replaced and receiver hygiene maintained.

Personal FM Systems

These wireless communication devices act much like a radio station. FM systems have a transmitter that accepts microphone input and transmits the FM equivalent signal. The FM signal is picked up by a receiver antenna, amplified, and transformed back into a sound signal. The speaker wears a compact transmitter and microphone while the listener wears portable receivers and earphones.

Wireless Headphones

There is no physical connection between the transmitter and the receiver in the headphone. Available in both FM and Infrared, the input can be through an audio jack plug on the TV, or through a microphone placed near the TV speaker. This system is gaining acceptance for home entertainment (e.g., TV, music, etc.) where a person needs a volume level that would disturb others.

FM Sound-Field Systems

These devices are essentially Public Address (P.A.) systems whose input device is a wireless microphone. The speaker talks into the FM microphone/transmitter that transforms and broadcasts the signal to an FM receiver/amplifier connected to, or physically located within, a loudspeaker. This system amplifies the speaker's voice to the point that the level of his or her speech is clearly audible above the backgrounds sounds.

Hearing aids that communicate sound information from one hearing aid to the other via wireless, amplitude modulated (AM) carrier appeared briefly in the marketplace. Some BTE hearing aids now employ built‑in or external FM receivers.

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Statement of the Problem

The following discussion is based upon issues raised during interviews and panels involving researchers, manufacturers and end-users.

• FM ALS transmissions are subject to radio interference and electromagnetic noise. FM (or related wireless) ALS having improved robustness to radio interference and electromagnetic noise are needed. In addition, FM ALS transmissions can spill over into adjacent environments and can easily be intercepted by anyone having an appropriate receiver. FM (or related wireless) ALS supporting private and secure communication with FM systems are needed. The performance of FM ALS receivers can vary with antenna orientation, the wearers body orientation, and environmental factors.
• FM ALS that automatically switch transmission frequencies are desired. Manual switching between transmission frequencies is a simple, low cost approach but is not user-friendly. Manual switching can be difficult for persons having low manual dexterity. In general, when manually switching frequencies, the continuity of communication can be broken and important information lost.
• FM ALS are limited in situations where a person is trying to listen to one voice in a crowd. FM ALS supporting multi-input, multi-listener communication are needed. Such systems would have many applications in small group settings such as meetings, banquets and family dinners. In one possible scenario, each speaker could have a short‑range, remote FM microphone (each its own frequency band). Each listener could have a small mixer, receiver with numbers and activity lights corresponding to each of the FM microphones. The listener selects the microphone that he/she wanted to "hear" by flipping a switch (the corresponding light would then come on). The selected transmission would be re­broadcast on the listener's private frequency and picked up by their built-in or external FM receiver. Many other scenarios are of course possible.
• FM receivers need to be simple, with very few visible controls, otherwise people may get intimidated by them. The cosmetic qualities of the technology need to be unobtrusive to be accepted by the user and non-user alike, in order to avoid stigma and abandonment.
• The brain can best process the speech signals when it is provided with binaural cues (head shadowing, time delays, and phase differences) in the differing sound signals received by each ear. Binaural hearing aids refer to the use of hearing aids in both ears where each hearing aid processes its sound signal independently. The user's residual ability to process binaural sound cues (e.g. head shadow, phase and timing) may or may not be significant. A communication link between these hearing aids would permit true binaural processing by the hearing aids themselves. This communication link should be wireless, interference-free, and have low power requirements. Hearing aid batteries currently supply approximately 2 mw of power.

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Issues to Consider

The following are issues to consider when developing new and/or improved FM Technologies.

The Need

• What are the important, unmet (or poorly met) user needs related to FM Assistive Listening Systems?
• What populations or demographics (e.g., degree of hearing loss, characteristics of hearing loss, cause of hearing loss, age, etc.) are most affected by these needs/problems?
• In which environments and for which activities is this need or problem most significant?
• What accommodations (or behavioral changes) do hearing impaired persons make in order to function in these environments and accomplish these activities?

State-of-the-Practice

• What FM assistive listening products are used by, or prescribed for, hearing impaired persons in order to address these problems or needs?
• What are the strengths (e.g., performance, cost, etc.) of these products?
• What are the weaknesses (e.g., performance, cost, etc.) of these products?

Future Technology and Products

• What significant technical improvements are needed?
• What technical barriers (e.g. environmental factors, power consumption, size, etc.) must be overcome in order to achieve these technical improvements?
• What breakthrough technologies (not present in current products) might better address the identified needs and problems?
• What technical barriers (e.g. environmental factors, power consumption, size, etc.) must be overcome in order to achieve these technical breakthroughs?

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References

Avrsono Company. (2000). Extended-Ear. Available: http://www.medicine-news.com/articles/devices/phonak.html (March 29, 2000).

Bakke, M, Levitt, H, Ross, M, & Erickson, F. (1999). Large Area Assistive Listening System: Review and Recommendations, Final Report to United States Architectural and Transportation Barriers Compliance Board. Jackson Heights: RERC on Hearing Enhancement.

Frost & Sullivan. (1994). World Audiology Product Markets. Available: http://www.frost.com (March 29, 2000).

Kompis, M, Feuz, P, Valentini, G, & Pelizzone, M. (2000). A Combined Fixed/Adaptive Beam Forming Noise-Reduction System for Hearing Aids. Available: http://www.orlinsel.ch/research/beam.htm (March 29, 2000).

National Center for Health Statistics. (1997). Advance Data: Vital Statistics of the Centers for Disease Control and Prevention (Number 292). Hyattsville, MD: National Center for Health Statistics.

Phonak, A. (2000). Biomedical Device Manufacturers - Medicine News. Available: http://www.medicine-news.com/articles/devices/phonak.html (March 29, 2000).

^* The study included non-institutionalized persons over the age of three.

^** Report published by the Hearing Industries Association Statistical Report, ending December 31, 1999. Numbers were based upon data supplied by 37 companies that agreed to participate in the report. Within this number the total number of hearing aids can be further broken down to: Behind-the-Ear (372,000 units), Completely-In-the-Canal (195,700), In-the-Canal (385,700), Body Aids, Eyeglasses, and others (53,200). Exports from the USA were estimated at 500,000 for this same time-period.

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