The key to wireless audiological breakthroughs lies in the ability for two hearing aids to communicate directly and continuously with each other and to external audio and communication devices. This article examines the potential benefits of digital wireless technology, using the Widex Clear440 and WidexLink devices as examples.
In two previous articles, we provided a description of wireless technologies1 and the rationale behind the WidexLink platform used in the Clear440 hearing aids.2 This proprietary wireless platform exchanges information (audio and data) between hearing aids and connects with audio devices in the wearers’ environments—all achieved through applications of both short-range and long-range wireless transmissions.
Figure 1. Short- and long-range transmissions achieved with the WidexLink wireless platform.
For the dispensing professionals, the real question is how WidexLink technology may accelerate the wearers’ use and acceptance of hearing aids. This may be best appreciated with knowing what audiological features are realized with the application of WidexLink and how they may benefit end users.
By way of review, Figure 1 shows the range of everyday devices that can be enhanced by the use of WidexLink. Communication among devices within the circle is achieved through short-range wireless transmission. The devices include the Clear hearing aids, the RC-DEX, the TV-DEX, and the M-DEX. Communication with devices outside the circle is achieved through long-range wireless transmission. They include computers, stereo hi-fi audio equipment, and portable entertainment systems such as MP3, television, cell phones, etc.
Easy Connectivity with External Devices and Better Sound Quality
The hearing industry has used wireless transmission technology for some time. The remote control devices that were used by many earlier programmable and digital hearing aids (and are still being used by some) employ short-range wireless transmission. The use of frequency modulation (FM) and its integration into the wearers’ personal hearing aids is an example of utilizing long-range wireless transmission technology.
This article was submitted to HR by Francis Kuk, PhD, and Bryan Crose, BSc, (pictured) of the Widex Office of Research in Clinical Amplification (ORCA), Lisle, Ill, and Thomas Kyhn, BSc, Martin Mørkebjerg, MSc, Mike Lind Rank, PhD, Magnus Nørgaard, PhD, and Helge Pontoppidan Föh, MSc, of Widex A/S, Lynge, Denmark. Correspondence can be addressed to HR or Francis Kuk, PhD, at .
However, these are examples of analog wireless technology, which has the limitations of high current drain, limited flexibility, and higher susceptibility to interference.2 The wireless technology that is being heralded today is digital wireless technology. It is reasonable to expect that digital wireless technology may realize higher performance than analog wireless technology, due to several factors:
TV/stereo reception. The environmental conditions in which TV viewing is done—such as the distance between the TV and hearing aid wearer, room acoustics, reverberation, background noise, etc—could degrade the quality of the TV signal when it reaches the hearing aids. Use of TV viewing devices may ensure excellent sound quality at a favorable SNR. Currently, there are several hearing aid manufacturers offering TV viewing devices. They typically have a transmission range of 10 m (33 ft), but they vary substantially in terms of their bit rate (from 120 kbits/s to 300 kbits/s), their audio bandwidth (from an upper range of 5000 Hz to 9500 Hz), and their transmission delay (from 35 ms to 150 ms). The latter affects the sound quality of the transmitted audio signals, with increased “hollowness” and echoic sensation as the delay is increased beyond 10 ms. Figure 2 shows that a delay as short as 30 ms would result in a metallic sound quality. Delays longer than 150 ms could result in a dis-synchrony between the visual and audio signals.
The TV-DEX by Widex is an optional assistive listening device (ALD) that allows communication between the TV (and other audio devices, such as a stereo player, MP3, etc) and Clear440 hearing aids. The TV-DEX includes a base station that accepts direct line input from the TV (and one additional audio player). It then transmits that input to the TV-DEX controller, which is placed close to the wearer when in use. When not in use, the TV-DEX can be inserted back into the base station to be recharged. TV signals from the TV-DEX are relayed to the Clear440 hearing aids. The maximum distance between the TV-DEX controller and its base station is 10 m, and the distance between the TV-DEX control unit and the Clear440 hearing aids is 1 m.
Figure 2. Perceptual consequence of transmission delay. As the delay moves upwards of 30 ms, sound quality starts to become an issue; delays longer than 150 ms can result in audio-visual dis-synchrony.
An important advantage of the TV-DEX is that Bluetooth is not used. Instead, a high-frequency carrier (2.4 GHz) is used to carry the TV signal in a stereo format at 212 kbit/s. With an audio transmission bandwidth from 100 Hz to 11,000 Hz, the TV-DEX reproduces rich and clear sound. To ensure excellent sound quality of the TV signals and perfect synchrony between the visual and acoustic signals, Echo-Free™ technology is utilized to achieve a delay of less than 10 ms.
The TV-DEX allows the wearers to control the volume of the transmitted TV signal and the hearing aid microphone signal separately. Thus, one may use the TV-DEX alone (Room Off) or with the mic on as a TV + HA (Room On) option.
Eco-Tech III technology is used to optimize the battery life of the hearing aids while the DEX devices are active. This results in less than 10% increase in current consumption during wireless transmission and lower current drain during “Room Off” operation than during normal use. Each charge of the TV-DEX controller unit allows approximately 10 hours of continuous use. This is significantly longer than the currently available commercial TV viewing devices, which typically last only 5 to 6 hours.
Communication on cell phone. While Bluetooth suffers from the limitations of high current drain and long delay, the fact that almost all commercial cellular phones use this protocol makes it necessary to include Bluetooth in the WidexLink wireless platform. The long delay of Bluetooth is still an issue; however, it is not as problematic when used with a telephone input. This is because no visual feedback is provided in cell phone communication, and direct sounds are not present to interact with the transmitted sounds to result in a metallic, hollow, or echoic sound quality.
The M-DEX by Widex is the wireless solution that provides connectivity between the Clear440 and the cell phone. When it is used as a cell phone, there is a microphone on the M-DEX that picks up the hearing aid wearer’s voice. For hands-free operation, the M-DEX may be worn around the wearer’s neck within a meter from the Clear440. This allows convenience of use and consistency of input with the use of cell phones.
Figure 3. Free-focus feature on the M-DEX showing the directions that receive the maximum sensitivity when the specific “-focus” is selected.
The M-DEX is also an optional master remote control (RC) that adjusts the volume and program settings on the hearing aids. There is also a built-in (or integrated) telecoil that picks up the inductive signals in the wearer’s environment and sends them to the hearing aids via short-range transmission. This may be a looped theater or classroom, or a TV that has been looped. Thus, one may still be able to utilize the inductive signal even if one’s hearing aids do not have a telecoil (such as in CICs).
In addition, a Free-Focus control allows the wearer to select which direction he/she wants to hear most (ie, optimize audibility). Figure 3 shows the sensitivity of the hearing aid array to sounds from different directions when a different “focus” is selected. For example, when the wearer selects the “right-focus,” the microphone on that side is set to an omnidirectional mode with no noise reduction, while the opposite ear has maximum noise reduction (18 dB on average). On the other hand, when a “front-focus” or “back-focus” is selected, the polar pattern of the microphone will switch to the appropriate directional mode.
Enhancement of Signal Processing Algorithms
A prime reason for digital wireless transmission is the potential of data exchange (audio and parameter settings) between the two Clear hearing aids at a very fast rate. Such an exchange increases the sophistication of the sound processing by the hearing aids and can potentially result in higher wearer satisfaction.
Audio sharing and Phone+. With the WidexLink wireless platform, the hearing aids wirelessly transmit audio data from one ear to the other ear using short-range transmission at 212 kbits/s. One application of such audio streaming capability is the Phone+ feature; during telephone use, the audio signal received at the ear is wirelessly transmitted to the opposite ear while the microphone on that ear is muted. In this way, phone conversation is heard in both ears with minimal noise interference from the environment. Because of binaural summation of loudness, the phone signal is also perceived to be louder, making it easier for the wearer to follow the conversation.
Data exchange/interear communication. The advantage of wirelessly exchanging data between two hearing aids is that each aid can evaluate information from the other device (such as levels and types of sounds received by the other hearing aid, evaluation of compression parameters, etc) so the two devices can work together for improvement of overall hearing aid performance.
Benefits of Integrated Signal Processing
The above benefits are made possible not only because wireless is available, but also the acoustic analysis performed by each individual hearing aid has become more accurate and precise with the use of C-Integrated Signal Processing (C-ISP) technology. An accurate acoustic analysis is a prerequisite for information sharing between hearing aids. The benefits realized by two hearing aids sharing information with each other are called InterEar benefits. They include:
Synchronization of volume control (VC) settings between hearing aids. For most people, the overall output of their hearing aids should be the same in both ears. If the wearer increases the VC on one ear for a front-facing sound, it is highly likely that the VC on the other ear should also be increased. By sending synchronization data every time the VC is pressed (ie, on demand), the VC settings between the two hearing aids are synchronized quickly. This is a benefit of convenience for the wearers, especially for those who use the hearing aids without a remote control.
Synchronization of listening program between hearing aids. One would also expect wearers to use the same listening program for both ears in an acoustic environment. A synchronized use of the same listening program is a convenience benefit for the hearing aid wearers. In cases where the wearer desires different programs on each side, the dispenser can select a “compound” program, which is a specific combination of listening programs for each ear. For example, a compound program may have the master program for the right ear and the telecoil program for the left ear.
Monitoring of partner hearing aid. Because both partners of a pair of Clear440 hearing aids are constantly sending data at a rate of 21 samples/s to each other, a loss of the synchronization data received by one of the hearing aids could signal a loss of communication between the two hearing aids. This may be the result of external electromagnetic interference, an expired battery, or when transmission distance has been exceeded. In any case, the hearing aid(s) with the working battery will set off a voice alarm and a blinking LED to warn the wearer of such an occurrence.
Because of the frequent update, the alarm serves as an “early-warning system” for the wearer to check the other hearing aid. It can also help prevent the loss of a partner hearing aid (although it is not intended as a tool to locate a missing partner hearing aid!).
Coordination of compression. A compression hearing aid—especially those with fast attack and release times—provides more gain for lower input level sounds and less gain for higher input level sounds. This compensates for the reduced dynamic range of the hearing-impaired ear so that soft sounds are audible and loud sounds are comfortable. While this mechanism is acceptable when the compression hearing aid acts alone, it could be confusing for a wearer to localize a sound source when these compression hearing aids are worn in a binaural fashion (ie, the majority of users today). This is because the interaural intensity cue, an important cue for localization of high frequency sounds, is disrupted.
The following example may help explain the situation. Imagine a sound being presented to the right side of a hearing aid wearer. The sound reaches the hearing aid on the right at a higher intensity level than that on the left because of the head-shadow effect. The relative intensity difference between ears is the inter-aural level difference (ILD). If the wearer has linear hearing aids on both ears at the fixed gain setting, the output of the hearing aids would maintain the natural ILDs.
However, if the hearing aids are fast-acting compression hearing aids, the gain on the right hearing aid will be lower than the gain on the left hearing aid because the input level on the right is higher. This results in a reduced ILD, which could lead to an increase in localization errors in quiet.
Figure 4a-c. Illustration of the interaural level difference (ILD) in an a) unaided or linear hearing aid condition; b) in an aided condition with fast-acting compression but without interear data exchange; and c) in an aided condition where coordinated compression is used.
There are two approaches to preserve the ILD. One is through the use of compression circuitry with purposely longer attack and release times (ie, slow-acting). Kuk3 provided a rationale and explanation on the action of slow-acting compression. Briefly, such a circuit maintains the short-term intensity difference of sounds but alters their long-term intensity relationship. Thus, the ILD between ears is maintained. This has been the design rationale of all Widex hearing digital hearing aids since the earliest days of the Senso in 1996.
Another approach that would preserve ILD is to share information of the input level at each hearing aid microphone and use the higher input level to set gain for both hearing aids according to the input-output (I/O) characteristics. This maintains the ILD between ears and is shown in Figure 4c. The use of coordinated, slow-acting compression would further ensure that such cues are preserved.
More accurate identification of feedback. An important objective in designing an active feedback cancellation system is to make sure that the signal identified as feedback is indeed feedback and not a musical tone. Otherwise, these signals will be cancelled unnecessarily and poor sound quality and/or intermittent periods of silence may result.
Many of the feedback issues have been addressed by Widex through the use of ISP technology. The use of multiple feedback cancellation paths within each microphone characteristic helped to ensure minimum risk of feedback with changes in polar pattern4 in all Inteo and Mind hearing aids.
In the Clear hearing aids, wireless communication between hearing aids allows further ascertainment about the nature of a questionable feedback signal. In this case, because the input to the hearing aids can be synchronously monitored, each hearing aid of a binaural pair can compare the input to the other hearing aid with its own input. A feedback signal will more likely be greater on one side than the other (Figure 5, top); whereas an external sound will more likely arrive at the microphones of both ears at a similar magnitude (Figure 5, bottom). Thus, by comparing the inputs between ears, one can further improve the accuracy of the feedback identification algorithm.
Figure 5. Input spectra of sounds measured at the microphones of a binaural pair of Clear440 hearing aids. On the top, where the input from the right ear is higher than the left ear, it is assumed that the right ear has a feedback problem. On the bottom where the inputs are identical between ears, it would suggest natural sounds reaching both ears.
The increased stability against feedback reduces the likelihood of unnecessary feedback. This leads to the use of more available gain and further ensures a more natural sound quality.
InterEar (IE) Zen. One of the unique features of the Clear440 is the availability of the IE-Zen program. This is an optional listening program where the wearers can have access to randomly generated fractal music with the push of a button.5
Zen is designed as a tool for relaxation and tinnitus management. Its efficacy for both functions (relaxation and tinnitus) has been demonstrated in several studies.6,7 The ability of the Clear440 hearing aids to wirelessly transmit data between ears at a fast rate (of 21 times/sec) allows each hearing aid to know if they are worn in a binaural or monaural mode. If only one aid is worn (ie, monaural mode), the Zen program proceeds to generate the full range of tones like it does in the Mind hearing aids; if binaural Clear440s are worn, the tones generated from each ear are coordinated to be complementary to each other. For example, while the current Zen may generate tones 1, 2, 3, 4, 5, 6 on both sides, the IE Zen worn in the binaural mode may generate tones 1, 3, 5 on one side and 2, 4, 6 on the other ear. This provides a more pleasant and relaxing experience than the uncoordinated Zen tones.
Coordination of noise reduction modes. Speech understanding in noise is the most sought-after benefit from hearing aids. The problem has been approached by Widex with the use of the High Definition Locator directional microphone system and a single-microphone solution using two noise reduction algorithms.
The Classic Noise Reduction (CNR) algorithm identifies continuous unmodulated signals as noise during silent pauses, then reduces gain in the appropriate frequency channels. The amount of gain reduction is based on the overall input level and the signal-to-noise ratio.8
The Speech Enhancer (SE) algorithm identifies noise in a similar manner as the Classic NR, but it also considers the hearing loss of the wearer in its formulation of gain reduction. In some frequency regions, it may increase gain in order to maximize the Speech Intelligibility Index (SII), as shown in the top row of Figure 6. Peeters et al9 reported on the rationale of these two algorithms and showed that the SE improved the SNR by 2 to 3 dB.
Figure 6. Illustration on the mechanism of the IE-speech enhancer. When IE is activated, speech detected on the dominant side will maintain maximum speech intelligibility index (SII) with gain increase, while the other side will reduce gain for the noise and not increase gain for speech on that side.
The IE-speech enhancer (IE-SE) noise management program brings noise reduction to a higher level of sophistication. By sharing the results of the acoustic analyses conducted between ears wirelessly, each hearing aid decides if it has a dominant speech input or dominant noise content. Once that decision is made, the side with the dominant speech will be set to the SE noise reduction to optimize the SII through appropriate gain reduction AND gain increase. The side with the dominant noise will be set for SE but with gain reduction only. In essence, it raises the level of the speech input on one side and reduces the level of the noise input on the opposite side (Figure 6, bottom).
Almost all modern hearing aids are programmed with computers. Not too long ago, hearing aids had to be physically connected to an interface called the Hi-Pro box, which in turn was connected to the computer via cables. This tied the clinicians and the wearers to the computer during programming. It also required manufacturer-specific and model-specific programming cables.
The application of Bluetooth in the wireless Noahlink programmer is a major step forward. It brings flexibility and speed to hearing aid programming. The Noahlink is wirelessly connected to the computer via Bluetooth, and the hearing aids are physically connected (via cables) to the portable Noahlink. This arrangement provides tremendous flexibility and efficiency to the programming over the wired interface Hi-Pro box. Tasks such as paired comparison of program settings, real-time display of input to the hearing aids,10 and increased speed of programming are possible. It also frees the wearers from being “tied” to the programming station, allowing movement of the wearer into different acoustic environments during programming. A practical advantage is that clinicians can perform hearing aid programming outside a booth while patients sit inside the booth.11
Despite the wireless nature of Bluetooth, the wearers’ hearing aids are still physically connected to the Noahlink via connecting cables. Different programming cables are needed for different manufacturers and for their various models. On the other hand, one can replace the cable functions by integrating short-range wireless transmission within the current Noahlink Bluetooth. A new programming device, the nEarCom, is a “neck-hook” attachment to the current Noahlink interface that enables data to/from the hearing aids to be transmitted wirelessly to Noahlink. The advantage of the nEarCom is that no programming cables are needed regardless of the hearing aid styles (such as BTE vs CIC style) for the participating manufacturers. Only a manufacturer-specific programming module needs to be inserted into the neck hook for access. This removes one source of clutter and/or confusion in the hearing aid clinic and streamlines programming.
The key to wireless audiological breakthroughs lies in the ability for two hearing aids to communicate directly and continuously with each other and to external audio and communication devices. The WidexLink digital wireless transmission technology provides this convenient physical basis for more thorough analysis of the environment. It also provides a more flexible and sophisticated processing that allows hearing aid wearers better control of their acoustic environments. The end result is a richer and cleaner sound quality, which may further improve wearer satisfaction for hearing aids. In selecting a wireless hearing aid system, it is important that clinicians are fully aware of the wireless features and how they may help their patients. Wireless brings the world closer—clearly and conveniently.
- Kuk F, Crose B, Korhonen P, Kyhn T, Mørkebjerg M, Rank M, Kidmose P, Jensen M, Larsen S, Ungstrup M. Digital wireless hearing aids, Part 1: A primer. Hearing Review. 2010;17(3):54-67. Accessed May 1, 2011.
- Kuk F, Korhonen P, Crose B, Kyhn T, Mørkebjerg M, Rank ML, Kidmose P, Jensen MH, Larsen SM, Ungstrup M. Digital wireless hearing aids, Part 2: Considerations in developing a new wireless platform. Hearing Review. 2011;18(6):46-53.
- Kuk F. Rationale and requirements for a slow acting compression hearing aid. Hear Jour. 1998;51(6):45-53,79.
- Kuk F, Jessen A, Klingby K, Henningsen L, Peeters H, Keenan D. Changing with the times: additional criteria to judge the effectiveness of active feedback cancellation algorithm. Hearing Review. 2006;13(10):38-48. Accessed July 11, 2011.
- Kuk F, Peeters H. Hearing aids as music synthesizer. Hearing Review. 2008;15(11):28-38. Accessed July 11, 2011.
- Sweetow R, Henderson-Sabes J. Effects of acoustical stimuli delivered through hearing aids on tinnitus. J Am Acad Audiol. 2010;21(7):461-473.
- Kuk F, Peeters H, Lau C. The efficacy of fractal music employed in hearing aids for tinnitus management. Hearing Review. 2010;17(10):32-42. Accessed July 11, 2011.
- Kuk F, Ludvigsen C, Paludan-Muller C. Improving hearing aid performance in noise: challenges and strategies. Hear Jour. 2002;55(4):34-46.
- Peeters H, Kuk F, Lau C, Keenan D. Subjective and objective measures of noise management algorithms. J Am Acad Audiol. 2009;20(2):89-98.
- Kuk F, Damsgaard A, Bulow M, Ludvigsen C. Using digital hearing aids to visualize real-life effects of signal processing. Hear Jour. 2004;57(4):40-49.
- Ingrao B. Bluetooth technology: toward more wireless hearing care solutions. Hearing Review. 2005;12(1):26-27,88. Accessed July 11, 2011.
Citation for this article:
Kuk F, Crose B, Kyhn T, Mørkebjerg M, Rank ML, Nørgaard M, Pontoppidan H. Digital Wireless Hearing Aids, Part 3: Audiological Benefits. Hearing Review. 2011;18(8):48-56.