By Tammara Stender, AuD
The ReSound Verso’s new Binaural Fusion technology strategy is detailed, along with the use of 2.4 GHz device-to-device wireless communication to provide greater hearing benefit to users. The introduction of the Invisible-In-the-Canal (IIC) model are also discussed.
Natural design is the pinnacle of functionality to which technology designed by humans can only aspire. Normal hearing and the brain’s natural processing abilities cannot be duplicated by machines such as hearing instruments. With this in mind, there are two approaches to hearing instrument design: with and without respect for naturally occurring processes.
On the one hand, hearing instrument technology can be designed to fulfill a given need—such as improved signal-to-noise ratio—without regard for the natural workings of the human auditory system. However, when hearing instruments work in isolation of each other, or make decisions without allowing for user choice of the most important sound source, an unnatural auditory experience can result. On the other hand, if the human auditory system is used as a guide and as “the standard” to which technology should be held accountable, the focus switches from the technology in and of itself to the hearing aid user—the individual.
ReSound has historically based its hearing systems on our understanding of the natural workings of the human auditory system. With these considerations in mind, the company is launching its latest hearing instruments designed to support natural processes: the ReSound Verso.
The Verso product family is the first in the hearing instrument market to offer device-to-device wireless transmission using 2.4 GHz wireless technology. The development of this technology for use in hearing instruments also has contributed new knowledge in the field of wireless research, as it was previously considered impossible to achieve device-to-device wireless communication in the 2.4 GHz frequency band. This wireless communication utilizes ear-to-ear technology in a way that supports the brain’s natural processing of sounds and is specifically aimed at providing user benefits in complex and changing environments. Binaural Fusion technology incorporates innovative approaches to directional processing and environmental steering of features.
Binaural Fusion is not the only way device-to-device communicative capabilities are utilized with ReSound Verso products. Traditional automatic directional switching between omnidirectional and directional processing depending on the sound environment is further enhanced by inter-device communication to result in the new Synchronized SoftSwitching. Phone use is made easier with Comfort Phone, which improves on ReSound’s PhoneNow feature to automatically reduce gain for the non-phone ear. And finally, traditional applications for device-to-device communication, Synchronized Push Button and Synchronized Volume Control, streamline the usability of Verso hearing instruments.
In addition, ReSound Verso offers other advancements apart from device-to-device communication technology. The new Range II integrated circuit affords lower power consumption, sound quality improvements, and greater memory capacity. A new version of digital feedback suppression, DFS Ultra II, provides better control against feedback and sound artifacts while also including a new setting designed to improve sound quality for music listening. The Verso family includes a full product line-up, including a new model: the Invisible-In-the-Canal (IIC) device. The Aventa 3.4 fitting software provides an additional compression threshold and fine-tuning control, improving fitting flexibility.
Verso also continues the tradition of Surround Sound by ReSound, which strives to replicate the way the ear receives and processes sounds naturally. WARP processing and Wide Dynamic Range Compression (WDRC) model the signal to preserve temporal information and restore non-linearity. NoiseTracker II cleans both steady-state and multi-talker babble noise from the signal. Directional Mix, a frequency-dependent approach to directional processing, balances the signal by eliminating traditional sound quality and low-frequency audibility problems. Additionally, frequency-dependent directional processing preserves spectral cues for better front-back localization abilities.1 Stabilization of the input signal by the new DFS Ultra II eradicates feedback and sound artifacts. The Binaural Fusion strategy is designed to complement and enhance Surround Sound.
Binaural Fusion for Natural
Human Auditory Processing
The human brain receives auditory inputs from each ear and integrates them into a mental representation of the sound environment. One method in which the brain organizes these acoustic inputs into a complete portrayal of the sounds around the listener is termed “auditory scene analysis.”2
The theory of auditory scene analysis describes the way listeners are able to discriminate different sound sources in the overall acoustic environment and attune to a particular signal of interest to them. For example, if a person is talking with a friend on a busy shopping street, she can tune-in to the friend’s voice in the midst of other people’s conversations and surrounding noises (Figure 1). Auditory scenes are analyzed by the brain using “bottom-up” and “top-down” processing. “Bottom-up” processing involves how all the sounds in the acoustic environment are perceived. Higher-level “top-down” processing enables the person to focus on the signal of interest (in this case, the friend). Other sounds in the environment are suppressed in the listener’s brain so the signal of interest is more audible.
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| Figure 1. “Bottom-up” and “top-down” processing is involved in everyday situations. These processes in the brain allow listeners to detect sounds in the environment and choose to attend to the signal of interest. |
However, listening landscapes are often dynamic, and the signal of interest may change. If another friend calls the listener’s name from behind her, that signal may become the most important. Optimally, the hearing instrument user would be able to detect the distant voice even while providing directional benefit for the friend nearby.
ReSound’s new Binaural Fusion strategy re-establishes the synergistic relationship between human auditory processing in the brain and sensory inputs from the ears. With the focus directed away from the hearing instruments and toward the natural auditory processes, the technology plays a supporting role to the binaural processing capabilities of the brain. The Binaural Fusion approach finds the most intense speech signal in the listening environment and ensures it is audible, but goes one step further. By not making assumptions about the hearing instrument user’s signal of interest, it provides the necessary surrounding auditory information to the individual to allow for user intent to manifest. The user is in control, and can choose to attune to or ignore sounds in the environment.
Binaural Fusion puts the emphasis on providing the most advantageous auditory information to the brain, which allows for these natural higher-level processes to occur. The sound environment is modeled at the level of the hearing instruments, which independently analyze the type and level of sounds in the listening environment based on the location of sound sources and the signal-to-noise ratio for speech. This bilateral assessment is exchanged between the hearing instruments to reach a comprehensive assessment of the listening setting. A solution is then derived for the most appropriate sound processing. This cooperative effort between the hearing instruments results in the most advantageous binaural microphone response, as well as coordinated noise reduction and gain settings for the listening environment.
Thus, the Binaural Fusion strategy introduces two new features: Binaural Directionality and Binaural Environmental Optimizer II. (For an in-depth discussion on the research and development of Binaural Fusion technology, download this PDF.)
Binaural Directionality. Binaural Directionality represents a large step forward in directional hearing aid processing. As a binaural strategy for microphone configuration steering between the two hearing instruments, it takes advantage of scientifically proven better-ear listening strategies, interaural phase differences, and auditory spatial attention strategies.3-7 Binaural Directionality provides the most advantageous microphone response for both hearing instruments in a binaural fitting, while still preserving the user’s ability to focus on the signal of interest. Every possible microphone response is offered by Binaural Directionality: bilateral omnidirectional, bilateral directional, and bilateral omnidirectional and directional, with either the right or the left hearing instrument assigned a directional response, based on the listening environment. Published research was instrumental in designing and determining which response would be the most natural, preferable, and advantageous for binaural processing in a given situation (Table 1).
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| Table 1. Binaural directivity responses and research supporting the instances in which these are most beneficial. |
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Binaural Fusion: An Analogy The Binaural Fusion strategy can be compared to a typical driving experience. Drivers tend to prioritize the view from the windshield as generally the most salient, to avoid collisions. However, it behooves drivers to monitor the rear- and side-view mirrors, to be aware of other surrounding drivers not necessarily in their direct line of sight. With Binaural Fusion, the view from the windshield (analogous to the loudest speech signal) is still prioritized and optimized for the best speech intelligibility. However, the option to glance in the rear- and side-view mirrors (akin to other surrounding sounds) is maintained. Binaural Fusion analyzes inputs from both ears to derive the binaural response, enabling the user to enjoy improved speech discrimination in noise in conjunction with better listening ease and monitoring abilities for surrounding sounds—in a single hearing instrument program. As a driver instinctively prioritizes the front view while keeping an eye on the surroundings, Binaural Fusion promotes more natural, instinctual listening abilities in complex and noisy environments. |
Based on this research, a bilateral omnidirectional response is chosen in quiet environments; a bilateraldirectional response is selected when speech is directly in front of the listener; and an appropriate asymmetric response (omnidirectional on one side and directional on the other) is chosen when speech is not directly in front of the listener in a noisy environment. This response allows users to detect other sound sources behind or around them, and turn to face these sound sources as they choose. The directional benefit is greatest for signals in front of the listener; yet the difference is that the user is not isolated and unaware of other, possibly important surrounding signals.
Research trial testing was conducted to ascertain the percentage of use time spent in each microphone configuration. Datalogging results were obtained from 29 subjects fitted with ReSound Verso devices programmed with Binaural Directionality over a 4-week period. The results indicated that the hearing instruments were on average in the bilateral omnidirectional mode 78% of the time, and were in some form of directional mode (bilateral directional or asymmetric directional) 22% of the time. These percentages were in agreement with other published studies regarding user-preferred microphone modes during weartime.8,16
Binaural Environmental Optimizer II. Environmental Optimizer II is an environmental steering feature that adjusts gain and NoiseTracker II settings based on the acoustic surroundings. With the incorporation of wireless information exchange between the hearing instruments, the new Binaural Environmental Optimizer II takes Environmental Optimizer II to the next level. Since the environment is more fully and comprehensively classified based on inputs from each hearing instrument in a binaural pair, better agreement and congruence in the sound environment information can be gleaned. As before, classification occurs based on the environment’s overall intensity level and the signal-to-noise ratio. Noise reduction and gain adjustments are made based on this classification, but are also synchronized and optimized between the two hearing instruments. This synchronization allows for a more accurate depiction of the sound environment for the user. Binaural Environmental Optimizer II can provide better listening comfort, audibility, and sound quality as the user encounters different environments throughout the day.
Solving Processing Problems with Music and Feedback Control Systems
Music is a completely unique auditory experience. Unlike most speech and other environmental sounds, it often has tonal qualities; for example, the notes in a flute solo or a piano sonata have distinct puretone-like qualities. Yet music is customarily treated the same as speech and other sounds by hearing instrument processing, including digital feedback cancellation. Some feedback management systems will misinterpret these puretones as feedback, and subsequently attempt to cancel them. This erroneous attempt to cancel non-feedback tones leads to sound artifacts, the insertion of artificial sounds by the hearing instrument. Since these artifacts are unnatural, sound quality is likewise degraded, and by extension, user satisfaction for music listening may decrease.
DFS Ultra II with Music Mode. With the launch of the ReSound Verso line, digital feedback suppression has been further optimized to correctly handle all sounds in the environment—including music. DFS Ultra II includes better precision and scaling to more accurately cancel feedback for all sounds.
For music, a specific setting of DFS Ultra II has been created: Music Mode. Music Mode is distinct from other settings of DFS Ultra II because it analyzes the input sound over a longer period of time. This allows for even more accuracy when distinguishing true feedback from other tonal input sounds, such as those commonly found in music. Music Mode provides a built-in mild level of Whistle Control. Due to its longer analysis time, Music Mode is considered a less-aggressive feedback cancellation setting than other settings of DFS Ultra II, which were designed for speech and other environmental sounds. (For further discussion into the development and research behind DFS Ultra II with Music Mode, visit: http://tinyurl.com/bt9b9f9.)
A New Solution for Phone Use
Adequate phone use is a necessity for most hearing instrument users. However, it poses a unique set of challenges due to the lack of visual cues and the high likelihood of background noise in many situations. Modern phone solutions with hearing instruments have made recent strides toward ameliorating these difficulties. The latest MarkeTrak VIII survey17 reported users of current hearing instruments experience a 60% reduction in hearing handicap. Introduced with the Verso line, ReSound offers another solution to the menu of options for improving phone use with hearing instruments. (For a full menu of solutions, visit http://tinyurl.com/bb3k97x.)
Comfort Phone. Comfort Phone utilizes ReSound Verso’s device-to-device wireless communication to enhance the PhoneNow feature. PhoneNow automatically switches the hearing instrument program to a telecoil or acoustic phone setting when a phone with a small magnet attached is brought near the hearing instrument. Comfort Phone improves on the PhoneNow feature by automatically reducing gains by 6 dB for the non-phone ear. When PhoneNow is deactivated by removing the phone, Comfort Phone automatically restores the original or optimal gain for the user’s environment. This reduced amplification for other sounds and background noise lessens the listening effort and strain for the user. However, the minor gain reduction still affords hearing instrument users some degree of environmental sound awareness, which may be beneficial if they decide another sound source in the background is more important than the phone conversation. The end result of Comfort Phone technology is that the phone experience becomes easier while the user maintains a degree of natural sound awareness.
The IIC: More than Cosmetic Appeal
Invisible-In-the-Canal devices are very popular for the obvious reason that they are so discreet and cosmetically appealing. Yet they offer more benefits than what is seen at first glance. Due to the deep placement of the microphone within the ear canal, wind noise is nearly eliminated. The anatomical structures of the external ear shield the microphone from the turbulent air flow created when wind strikes a surface.18 Another advantage of deep microphone location in the ear canal is the maintenance of spectral cues used in localizing sound sources in the environment. Since the high-frequency pinna effects are preserved, natural front-back localization abilities are maintained.19-22 Finally, deep placement of the microphone in the canal enables many users to hold the phone normally to their ears, with feedback controlled both by the distance of the phone to the microphone and by the digital feedback suppression system.
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| Figure 2. The Verso IIC is discreet and cosmetically appealing. |
The ReSound Verso IIC (Figure 2) offers each of the user benefits common to other IICs, but provides additional advantages for both the user and the hearing professional. The Surround Sound by ReSound experience is included in all Verso IIC devices, and includes advanced WARP processing and leading features such as NoiseTracker II and Environmental Optimizer II. Environmental Optimizer II automatically adjusts the gain and noise reduction settings as the listening situations change, reducing the need for manual program or volume controls. Further, no special or exceedingly deep earmold impression is required. (For more information on the Verso IIC, visit: http://tinyurl.com/arm23ef.)
Tammara Stender, AuD, is senior audiologist at GN ReSound Global Audiology in Glenview, Ill. CORRESPONDENCE can be addressed to Dr Stender at: [email protected] |
Summary
ReSound’s use of 2.4 GHz device-to-device technology in the Verso line focuses on supporting natural processing abilities by the human brain. The new Binaural Fusion strategy puts the hearing instrument user in the driver’s seat, allowing for user intent and determination of the most salient sound source in the environment. ReSound’s judicious use of device-to-device communication and technology also affords better listening experiences for two notoriously difficult situations: on the phone and while enjoying music. With a full product line-up, including the Verso IIC, a wide range of individuals can experience the difference when natural processing abilities and technology converge.
References
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