Breaking It Down | MFI Hearing Aids

Jennifer Groth, ReSoundBy Jenny Groth

Until now, it has not been feasible to implement Bluetooth directly in hearing aids mainly due to power constraints, thus necessitating a wireless accessory for any communication with cell phones or smart devices. However, Bluetooth version 4.0 includes a low energy feature which meets the power constraints of hearing aids. Branded by the Bluetooth SIG (Special Interest Group) as “Bluetooth Smart,” this technology is a “power-friendly” version of the open Bluetooth wireless standard and has become popular particularly for monitoring devices like heart rate monitors and fitness trackers.

The availability of the low energy Bluetooth feature has made MFi hearing aids possible. An MFi hearing aid connects wirelessly to iOS devices without any additional hardware. According to Apple, “these hearing aids deliver a power-efficient, high-quality digital audio experience” and also allow users to manage their hearing aids from their iPhone devices.

A major part of the challenge of developing MFi hearing aids is mastery of robust radio frequency transmission at 2.4 GHz. Because its digital wireless hearing aid system was already based on radio frequency transmission at 2.4 GHz rather than the more common near-field magnetic induction (NFMI), ReSound was in a favorable position to develop an MFi hearing aid – the ReSound LiNX – relatively quickly.

Fresh appleSo what can MFi hearing aids do? One of the most attractive features of MFi is audio streaming in high quality stereo. Any type of audio played from an iOS device can be streamed to MFi hearing aids, including music, podcasts, games, FaceTime calls, Netflix or YouTube videos just to name a few. While all of these uses certainly can add to the enjoyment and utility of using an Apple device, perhaps the most significant benefit is the streaming of phone calls to the hearing aids. Phone use is made difficult by the absence of visual cues, inappropriate or inadequate coupling to the phone and the presence of background noise. Not surprisingly, many hearing aid users feel they are unsuccessful on the phone.

Receiving the phone signal directly from the phone to the hearing aids with no intermediate accessory provides an obvious benefit in terms of convenience to the user. In addition, it has been established that a bilateral wireless signal optimizes benefit for hearing on the phone1. A recent study of the benefit of different phone options including MFi reinforced this finding, but also suggests that MFi may provide additional benefit compared to streaming the phone signal via a wireless accessory with conventional Bluetooth2. In this study, listeners were administered an adaptive speech-in-noise test with the speech presented unilaterally in four different telephone conditions:

  1. Using the hearing aid microphone (“Acoustic Phone”)
  2. Using the hearing aid telecoil (“Telecoil Phone”)
  3. Streaming the phone signal via Bluetooth through a wireless hearing aid accessory (“Phone Clip+”)
  4. Streaming the phone signal directly from the iPhone (“ReSound LiNX MFi”)

figure-groth-blogPerformance in all wireless conditions exceeded the “Acoustic Phone” condition. The average SRT scores in dB for the four test conditions including 95% confidence intervals are shown.  All conditions are unilateral, with the phone signal in only one ear. The authors also noted the greater variability for the “Acoustic Phone” and “Telecoil Phone” conditions than the two digital wireless conditions, which they attributed to individual difficulties in placing and maintaining the telephone correctly for signal reception. As a result they predict more reliable benefit with the digital wireless solutions. What is also striking about these results is that the MFi condition was significantly better than either the “Telecoil Phone” or “Phone Clip+” conditions. This was in contrast to the expectation that the two digital wireless phone solutions would yield equivalent results. The authors speculate that this may be related to a decline in signal quality caused by the extra link needed when using a Bluetooth-based hearing aid accessory (phone-to-accessory-to-hearing aids). As mentioned, MFi also gives users the opportunity to manage their hearing aids from the iOS devices. In the case of the

ReSound LiNX, the ReSound Smart™ app enables this functionality. First of all, the ReSound Smart app serves as a remote control for the hearing instruments. Users can change programs, adjust volume and choose the input to the hearing aids. One adjustment type allowed by the ReSound Smart app that typically is not available to hearing aid users is an adjustment of treble and bass. This can be particularly useful for specific listening situations, such as music listening. Additionally, this app offers the capability to associate specific hearing instrument settings including the listening program, volume and treble/bass adjustments with a geographical location. This functionality is called “geo-tagging.” Finally, a “find my hearing aid” feature can help locate a misplaced device, and tutorials provide usage and troubleshooting advice that is easily accessible.

This content was originally published on on May 7, 2014.


  1. Picou EM, Ricketts TA. Comparison of wireless and acoustic hearing aid-based telephone listening strategies. Ear & Hearing. 2011; 32(2): 209-220.
  2. Nesgaard Pedersen J, Kirkwood B. Speech Intelligibility Benefits of Assisted Telephone Listening Methods. In press. 2014.

© 2014 The GN ReSound Group, all rights reserved. Apple, iPhone, iPad and iPod touch are trademarks of Apple Inc, registered in the U.S. and other countries. Bluetooth is a trademark of Bluetooth SIG, Inc.

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10 thoughts on “Breaking It Down | MFI Hearing Aids”

  1. The one feature that would make this even better is if answering a phone call would mute the Linx other microphones. You can do this manually once the call is underway by opening the Resound app and muting the microphones for the duration of the call. Interestingly, the microphones are automatically turned back on when the call is completed. This would be a very nice feature to add if you have any ability to pass along to Resound. It makes a huge difference in hearing the other person.

  2. All this is well and good if, a big if, the HA’s stay paired. For example, this morning I woke turning on the bluetooth on my iPhone 5c. Then closed the battery doors on the HA. 15 minutes later I started streaming iTunes music to the HA’s. Walking in the street the commuter traffic got unbearable so I opened the Linx App and muted the mic. Worked fine on a 1 hr walk. Got home un-muted the mic, closed iTunes and put the iPhone in my pocket and went about my business. 2 hours later I opened the app and it ran for 2 minutes then told me that there was no connection. What I’ve been doing for almost a month of trial with the Linx is to shut down the iPhone and restart it. Then and only then will they stayed paired. I shut down now on average 4 x per day:Even with fresh batteries I still need to do this. Not a good user experience.
    By the way my batteries are not giving me any low battery waring until about day 5, not bad but is this causing the bluetooth issues I’m having. I called the tech and ReSound and she told me that if I wanted to always stay paired I needed to change them every 2 days, Really?
    I keep posting on many blogs & websites and reading that I’m not the only one having issues.

    1. Hi Frank. We’re sorry to hear about your pairing issues. We know you’ve already discussed this with one of our consumer support representatives, but if you’d like to discuss further, we’d be happy to connect you with someone. Just let us know and we’ll have someone reach out to you.

      1. Gary Hitchcock

        This is pretty much the canned response to any comment about problems.Telling the customer to call tech support is just avoiding answering the question. Tech support seems to be clueless in many cases.

        Suggestion to Resound social media representative: provide specific, technical (OK, semi-technical) responses that address the issue and what Resound is doing to resolve the problem. Maybe even the solution.

        BTW, Frank. You’re right. Many people still have pairing problems. Just last night, I could not my Linx to pair with my iPhone 6 Plus running iOS 8.3. i’ve had them since August, 2014.

        The short battery life is due to a bad design decision on the part of Resound. The 312 was selected to provide the thinest, lightest HA they could. The de facto industry standard 13 battery should have be selected, certainly in the high powered version. my loss is in the 80 – 90 db range.

    1. Hi Harold, you can use the “Add a place” feature to save settings to programs, based on your GPS coordinates. If you use different programs frequently at home or work, for example, you can make your preferred settings in a specific program, then “add a place” to save the settings (this video might help: If you’re streaming audio from your phone into your ReSound LiNX, you won’t be able to save these settings. However if you do frequently adjust volume or have certain preferences when you’re streaming (if you prefer more bass), you could consider having your hearing healthcare professional change the overall settings within the software they used to fit you. Hopefully this answers your question, but if not, I’d be happy to connect you with one of our consumer support team members to walk you through this in more detail. Let me know if you’d like someone to reach out to you!

      1. Thanks for your quick and helpful reply.
        One more question . . . can I edit the names of the places? For example, it appears possible to have more than one place at the same geographical address? I use different settings for my office and the dining room of our retirement complex – – both have the same geographical address, and I would like to edit the names to reflect this.

      2. When you use the “Add a place” feature, you won’t be able to change the names at this time. And, since both your office and dining room have the same geographical address, the ReSound Smart app won’t differentiate between rooms. However, your hearing healthcare professional can set up a different programs for one of the locations (for example, with more gain and noise reduction for the dining room) so instead of changing “places,” you can just change “programs.” Let us know if there is anything else we can do to help!

  3. I have a problem with the linx hearing aids… I am an Audiologist from South Africa and it has happened with 2 different patients – when streaming sound from their iPhone, the sound is mickey mouse like? It is not clear at all. Please help!

    1. Hello Chezne, thank you for contacting ReSound. This blog is monitored by the U.S. subsidiary of ReSound but we will pass your message onto the appropriate party at our headquarters to get back to you.

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