By Barbra Timmer, MAudSA, MBA

Wireless connectivity is a term embraced and seemingly well-understood by the hearing care industry. The ability to connect hearing aids to other audio devices, such as MP3 players, personal computers, and television, has meant tangible benefits to patients with hearing loss. What appears to be less well understood is how wireless communication allows a pair of hearing aids to connect with each other, and how the wireless frequency inherent in the hearing aid technology enables, or limits, the features that can utilize this capability.

A pair of hearing aids can transmit data codes to synchronize with each, or can transmit full audio signal to stream to each other. Moore1 distinguished these two capabilities as exchanging either control signals (in the case of synchronization) or audio signals (in the case of streaming). In part, the confusion about these different levels of wireless functionality may be due to hearing aid manufacturers applying the label “binaural processing” to all such wireless functionality, even when referring to simple command/control exchange. In actual fact, very few hearing aids available today do both.

All major hearing aid manufacturers today offer hearing aids that synchronize through the exchange of control signals. Simple command codes are exchanged between such devices to synchronize aspects such as volume, programs, and compression characteristics, for certain features such as microphone mode. While there is agreement in the benefit of synchronized volume or program changes for user convenience, hearing performance benefits are scarce, with the literature showing limited improvement.

Sockalingam et al2 investigated localization and sound quality differences in synchronized and unsynchronized modes. Although localization was significantly better when the hearing aids were synchronized, the user preference for this mode was unclear, and depended on the listening situation. Smith et al3 reported no significant difference in using hearing aids in a synchronized versus an unsynchronized mode when measured by the Speech, Spatial, and Qualities (SSQ) of Hearing Scale.

The final reported preferences for wearing the hearing aids in the synchronized mode may be attributed to a halo effect, as the users were not blinded to the hearing aid mode. Kreisman et al4 showed improved speech understanding in noise when using a synchronized pair of devices; however, because the comparison was to older-technology unsynchronized devices with a narrow frequency range, it is unclear if the benefit can be ascribed to the synchronization or to the difference in bandwidth between the two pair of hearing aids. The lack of empirical data to support the benefit of synchronizing hearing aid features may be explained by Beutelmann and Brand5 who found that patients with a hearing loss were less able to make use of binaural cues than those with normal hearing.  

Moore1 was not alone in suggesting that streaming audio signals between hearing aids could “lead to further benefits for the hearing impaired.” Sandrock and Schum6 also envisaged this capability would improve “both directional hearing and listening in noise.”

Moore1 did point out that further investigation was necessary to examine the extent of the benefit. A number of such investigations have since been conducted, looking at the benefits of such binaural streaming when communicating in noisy environments, in windy situations, on the telephone, and in the car.

Noisy Environments

The development of directional microphones has been the hearing aid technology most instrumental in improving speech understanding in noisy environments. A review of the evidence for directional microphones by Bentler7 supports the technology available at that stage (in 2005), and further progress has been made in the 8 years since her review was published. Although the benefits of directional microphones may be reduced in the case of an open fitting, studies show that it is still more beneficial than using omnidirectional microphones.8,9

The ability to stream a full audio signal between two hearing aids allows an even greater benefit of directionality, as it incorporates not two microphones per ear, but a network of four microphones across two hearing aids. This creates more advanced beamformer polar responses that were previously unavailable with directional microphones in hearing aids that were either not linked or merely synchronized.

The result from this binaural beamforming, commercially available under the feature name StereoZoom, is greater speech understanding and user preference, compared to other advanced directional microphones.10-12

A recent study presented by Picou13 showed that, compared to the omnidirectional mode, the binaural beamformer improved speech recognition in noise, decreased listening effort, and improved recall. A speech recognition advantage also was found in comparison to an advanced monaural directional mode.

Timmer1 opt
Figure 1. The exchange of full audio data between hearing instruments facilitates binaural signal processing such as binaural beamforming.
Figure 2. The relationship between satisfaction and the number of environments in which the wearer benefits from their hearing aids. Adapted from Kochkin.27


Windy Situations

Wind noise is an environmental effect that can be disturbing to wearers of hearing aids. Kochkin14 reports that, in terms of signal processing or sound quality, MarkeTrak respondents were least satisfied with their hearing aid in wind noise.

Several solutions have been suggested in the past to combat this, from completely-in-the-canal fitting15 to various mixed omnidirectional and directional microphone modes.16 These clearly incorporate making a compromise, be it on hearing aid fitting style or speech understanding by reducing directional benefit.

The ability to stream a full audio signal between two hearing aids allows the pair of devices to detect where the better speech-to-noise ratio is and present only those low frequencies with the least amount of wind noise to the listener. A Phonak binaural streaming algorithm, called Speech in Wind, ensures not only comfort but also improved speech intelligibility in windy listening situations.17,18

Using the Telephone

Picou and Ricketts19 found that presenting the telephone signal to both ears resulted in significantly better speech recognition than a telephone listening strategy that presented the telephone signal to only one ear. Binaural telephone listening can be accomplished by using a relay or streamer that acts as intermediary between the telephone and the hearing aids. However, in technologies that allow for data streaming between two hearing aids, such a relay is unnecessary and the listener can enjoy binaural hearing on the phone simply by holding up the handset or mobile phone to one ear.20

In the Car

Among the various everyday listening situations, listening while driving a car may be one of the most challenging. Several studies have shown that the car is a common, complex, and loud sound environment for patients.21-23 A number of hearing aid features have been developed to deal with this, such as using asymmetrical directional settings or asymmetrical gain settings in a pair of hearing aids. These tactics can help make the listening situation more comfortable, but may not enhance speech understanding.

The Phonak auto ZoomControl feature harnesses the streaming ability of Binaural VoiceStream Technology to improve speech understanding when the signal that the listener wants to hear may not be in front of them, such as when driving a car. When comparing different hearing aid technologies in a car listening situation, Stangl et al24 showed that only the pair of hearing aids that streamed the full audio signal from one hearing aid to the other was able to improve speech perception when the speaker was seated either next to the listener or behind them.

New Solutions for CROS and BiCROS Fittings

Another significant benefit from Binaural VoiceStream Technology is for those patients who need a CROS or BiCROS fitting. The Phonak CROS solutions no longer involve the use of cables, or audio shoes, but offer high-end signal processing and access to a large number of hearing aid features. This results in hearing performance and user preference not previously seen with CROS applications.25,26

Innovation with Purpose

As Kochkin27 suggests, the more listening situations in which hearing aids can satisfactorily perform, the more hearing aids, in general, would be recommended by those who wear them.

The ability to stream full audio data between two hearing instruments provides solutions for sound environments that have not been sufficiently addressed by any other hearing aid technology. It is such innovation with purpose that will support overall satisfaction with hearing aids.

BarbaraTimmer opt

Barbra Timmer, MAudSA, MBA, completed her Audiology studies at the University of Queensland in Australia, and her MBA from the Sydney Graduate School of Management. She joined Phonak in 1996 and transferred to its Swiss headquarters in 2010, eventually serving as the company’s director of audiology and education in charge of its Audiology & Training, Pediatric Audiology, Clinical Research, and Validation Teams. In 2013, she took on a new role with Phonak as research audiologist and is concurrently pursuing a research degree at the University of Queensland. CORRESPONDENCE can be addressed to: [email protected]



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