More On Our Recommendation For Remote Mic/FM Use For All Hearing Impaired Children

In a previous article on selecting the appropriate Phonak Roger receiver, we urged that all hearing impaired children use FM or digital Remote Mic technology to give them the improved signal-to-noise (S/N) ratio to increase their listening ease, hence reducing their cognitive overload; and in fact other experts with far more clinical and research experience than us have concurred (see Three 60 Minute Free Webinars On FM ALD’s You Must Watch). However, we received this thoughtful reply from Holly Teagle PhD, who is an audiologist we respect at the excellent UNC-Chapel Hill pediatric CI and ABI program; and we believe that her concerns are important enough to address in detail in this new, separate article.

Dr Teagle writes:

I work at a large pediatric cochlear implant clinic which uses all three cochlear implant manufacturers and serves a diverse population of children. While FM/DM use with cochlear implants can be successful, I highly disagree that it should be used with all children with cochlear implants. At our center we do not recommend use of this technology until a child’s programming levels are relatively stable, a detection audiogram of about 25 dB HL across frequencies has been obtained, and the child is able to participate at some level in speech perception assessment so use of the device can be verified. It is also important that recipients are reliable reporters of device function and sound quality. Additionally, the experience and knowledge of the person with the microphone and the environmental need should be considered. This excludes many CI children from being good candidates for FM/DM.

The Hearing Blog Replies:

Dr Teagle’s concerns are certainly valid, as improperly configured analog FM systems8, 11 can indeed do more harm than good, especially when there is interference present above the capture ratio (typically ≈2dB)1, 2 and the receiver circuit is unable to squelch, or discriminate out the spurious signal, as can happen with low power analog FM transmissions where the receiver demodulator2 is not driven to full quieting, i.e. the audio is not crystal clear like the FM broadcast audio you hear on your car radio. Basically, full quieting occurs whenever the receiver demodulator stage is driven into saturation, and no further improvement in SINADA (or approximately, S/N) occurs, no matter how strong the desired RF signal. So-called “digital FM” systems such as the Phonak Roger, Williams Digiwave, and Bellman Audio Domino do not suffer from these problems, as they all rely on 2.45 gHz digital audio transmission using slight-but-proprietary variations of the IEEE 802.15.4/6 Bluetooth 4.0 Low Energy/HIBAN protocol. As with any digital audio system such as the Sirius/XM receiver in your car, as long as the bits can be picked out of the noise, crystal-clear sound will be received, as any interference is absorbed and filtered out in the digital-to-analog conversion process.

In addition, trouble can arise with both analog and digital FM systems, as they can both suffer when the clinician makes a poor choice by coupling a separate non-headworn receiver into the hearing aids or CI’s worn by infants & toddlers. These poor choices fall into two primary categories: Using the ergonomically dodgy direct audio input (DAI) cables between the receiver and headworn devices; or much worse, using baseband induction (“hearing”) loop transmissionD between the receiver and headworn instruments, whether it’s using a neckloop or “looped” classroom, as both orientation of the magnetic flux lines to the induction pickup “T-coils” changes with head motion, and unexpected electromagnetic interference make this obsolete technology never suitable for children too young to report a reception problem.

However, at this point the astute reader may have noticed that we did not include “Remote Mic” or “RM” in the above two paragraphs, as this technology is both all-digital and transmitted directly to the hearing aids or CI’s, either directly via the ReSound Unite wireless system, also available with licensee Cochlear’s Nucleus 6 CI4, 5 and BP-400 & 500 BAHA devices, or through a bodyworn streamer dongle, such as those from Phonak, Siemens, and Unitron. In addition to the ReSound/Cochlear Unite Mini Mic, Phonak has their similar 2.45 gHz “Roger” digital transmission system available with headworn micro-receivers, including purpose-built for CI’s & their own hearing aids, and universal “X” receivers that plug into many other hearing aids; however as we pointed out in October, the Roger system was not incorporated into Phonak’s new Venture platform hearing aids, even as an extra-cost option.7

One of the features we really like is passive or active monitoring of hearing aid and speech processor performance, either through status lights as found on ReSound UP Smart pediatric aids (not available in US or Canada) or two-way telemetry; and to this end the Phonak Roger system provides bidirectional link status monitoring when an Inspiro transmitter is used with Roger X (02) universal or other dedicated  (02) “pediatric” receivers.3

However, as we have uncovered, there are several caveats to using headworn Roger receivers, especially the universal X receiver, that are germane to their use on infants and toddlers:

  • We have uncovered an undervoltage coordination problem causing radio dropout when the X (03) [and probably X (02)] receiver is used with the ReSound Enzo hearing aid: As it turns out, when the battery voltage drops below a certain threshold in the 1.15 volt range the radio drops out, while the low battery alarm on the Enzo does not chime for many hours. We have alerted both ReSound and Phonak to this problem; however neither manufacturer has addressed it at the time of this article;
  •  According to Siemens officials in Piscataway, when the Roger receiver is used with their Micon series hearing aids, audible “pumping” occurs, which is an interaction between some sort of PID or other control vector in the transmitter &/or receiver and the wide dynamic range compression (WDRC) in the Siemens aids themselves. Phonak claims that the response of the system is linear up to a certain point and then goes into 10:1 limiting near the peak; however we also know that some noise reduction (hence at least one PID or other control vector) is used in the Roger Pen Mic when it is switched to “conference table” mode when laying flat. Siemens’ engineering staff in Germany has been in discussions with their Swiss counterparts at Phonak; however all that has occurred to date is finger-pointing at each other… And knowing our engineer brothers, we know which finger is doing the pointing;
  • Worth noting is that because both the Unite and Roger systems use a 2-way protocol for frequency-hopping coordination, meaning the receivers also briefly transmit back to the transmitter a data packet several hundred times per second, the added battery drain of about 3.0 mA for the first generation Roger receiver, 2.4 mA for their second generation deviceC and about 2.8 mA for the Unite system6 can make using a hearing aid fueled by a #13 battery — Especially these crappy “mercury free” cells — a dicey proposition at best; and also making a #312-powered aid out of the question. That Being Said, bidirectional link status monitoring is available when the Inspiro transmitter and -02 series “pediatric” receivers are used together, which mostly addresses this problem… Provided the parent or teacher pays attention, a salient point to which Dr Teagle alludes;
  • Especially for infants and toddlers we do not recommend using click-on direct audio input (DAI) boots, as they are notoriously mechanically unreliable.
    Click-on DAI boots are a no-no with infants and toddlers

    Click-on DAI boots are a no-no with infants and toddlers

    Instead, we recommend hearing aids that have the DAI socket on the chassis; or better, built into a field-replaceable battery door as found on the ReSound Enzo and corresponding UP Smart aids. [The reason we especially like the Enzo DAI setup is that here in the United States there is a tendency at schools to unplug the receiver at the end of each school day “for safekeeping;” however since a DAI socket only has a life of about 100 mating cycles, this means the aid must go back to the repair shop about twice a year where a new socket is soldered to the chassis, while on the Enzo it is simply swapped out on the desktop in about 30 seconds.]

There is a separate issue of using a digital transmission system when the audio must be relayed to the hearing aids using a streamer (dongle). Four of the “Big Six” hearing aid & CI companies — Sonova (Phonak, AB, & Unitron), Demant (Oticon, Bernafon, & Oticon Medical CI’s), Siemens, and Widex — use proprietary 10.6 mHz ISM digital audio transmission protocolsF between their streamers, acting as a relay between Bluetooth and other audio signals, and the low power radios in the hearing aids; compared to ReSound, Cochlear, and Starkey.

Phonak_Roger_and_ComPilot-2511-525px

Phonak ComPilot with Roger X(03) receiver plugged in and matching remote mic on the right, ReSound Enzo DAI battery door with Roger X(03) receiver plugged in on the left, Roger Clip-on Mic on the left, and Roger Pen Mic on the bottom

Whether to use one of these streamers on a pediatric patient to relay digitally transmitted audio is a decision the clinician needs to make on a case-by-case basis, as when 10.6 mHz is used as the final link to the hearing aids &/or CI’s, smaller hearing aids with #13 and even #312 battery power become acceptable due to overall lower current drain… But at the price of wearing the dongle around the neck, with the clinician and parents making the final call.

If a streamer is decided upon, there are still other landmines to avoid: Latency between the remote mic and the streamer itself, as some remote mics use Bluetooth transmission; and in fact Oticon’s RM solution is particularly dodgy, even with the Streamer Pro However, the Phonak/AB ComPilot I & II, Oticon Streamer Pro, and Siemens miniTec all have 3-pin DAI sockets on them so a Roger receiver can be plugged in.

One other landmine we uncovered in our Phonak training last November applies to bimodal (hearing aid + CI) patients: The new Venture platform hearing aids require the ComPilot II, while the older Quest platform hearing aids and Advanced Bionics Naida q70 speech processor require the original ComPilot, as the new ComPilot II is not backwards-compatible to the Quest and earlier platforms. Because of this, The Hearing Blog recommends the dedicated headworn Roger 17(02) and appropriate hearing aid FM receivers be used, as for infants and toddlers this is a more robust solution.

In short, although Dr Teagle’s concern about reliability for infants and toddlers is indeed valid, we believe from our own testing as well as others’ clinical experience such as at Hearts for Hearing8, 9, 10 that the newer all-digital UHF Roger and Unite systems are robust enough for this use, and will deliver the tremendous benefits of improved signal-to-noise to this population, hence our contention that all hearing impaired children of all ages be equipped with this vital FM/RM technology.

 Addendum:

Of course, as Jane Madell PhD helpfully points out in this video, FM systems only work when the teacher is wearing the transmitter, and it is switched on!

As we reported three years ago, individuals with hearing loss actually process sound differently in noisy environments, due to erosion of temporal resolution and processing in the presence of noise, demonstrating the need for the improved speech-to-noise level (S/N ratio) FM assistive systems provide. What’s more, even in relatively quiet settings, the reverberation time Tr (or T60) found in many rooms is often far in excess of the acceptable limit of 550 mSec.1 Basically, by using a wireless assistive listening system, the child will reap the low-hanging “listening ease” fruit that can be snatched just for the taking. To drive this point home, put your earbuds in and watch this independently produced demonstration, recorded in an actual Vermont classroom:

References:

  1. FM Reception – squelch, quieting & capture ratio: Ian Poole, Radio-Electronics.com;
  2. FM Demodulation / Detection TutorialIan Poole, Radio-Electronics.com;
  3. Selecting a Phonak Roger Receiver: The Hearing Blog, October 2, 2014;
  4. FDA Finally Approves Use of ReSound Wireless Accessories With The Nucleus 6 CI Processor: The Hearing Blog, September 14, 2014;
  5. ReSound & Cochlear Wireless Accessory Compatibility: The Hearing Blog, September 30, 2014;
  6. Coming This Week: The ReSound LiNX “Made For iPhone” Hearing Aid You Can Actually Use: The Hearing Blog, August 30, 2014;
  7. Sonova Panned By Stock Analysts Over Lack Of 2.4gHz Digital Connectivity In Venture Platform, Costco Backlash: The Hearing Blog, October 30, 2014
  8. Programming Cochlear Implants, Second Edition: Jace Wolfe PhD and Erin Schafer PhD.G Plural Publishing: ISBN-13: 978-1-59756-552-3 ISBN-10: 1597565520. Book review of first edition here; review of second edition in progress;
  9. AudiologyOnline.com recorded course #25544: Cochlear Implants and Remote Microphone Technology, Presented in Partnership with Seminars in Hearing; Jace Wolfe PhD. Abstract:
    Despite advances in cochlear implant (CI) technology and impressive outcomes for recipients, CI users often continue to experience difficulty understanding in noisy and reverberant environments. Performance in these situations may be improved with wireless remote microphone technology. This webinar reviews several studies that have explored the use of wireless remote mic technology for CI users based on the article published in Seminars in Hearing (volume 35, no. 3, August 2014) by the presenter;
  10. AudiologyOnline.com recorded course #25551: Use of Wireless Technology for Children with Auditory Processing Disorders, Attention-Deficit Hyperactivity Disorder, and Language Disorders, Presented in Partnership with Seminars in Hearing; Erin Schafer PhD.G Abstract:
    This webinar presents evidence to support the use of wireless, remote microphone technology for improving speech-recognition performance in noise and classroom-listening abilities in children diagnosed with auditory processing disorders (APDs), attention-deficit hyperactivity disorder (ADHD), and autism spectrum disorders (ASDs). Following the review of evidence, case studies will be presented to support device fitting procedures and to report performance on behavioral measures and subjective questionnaires following the fitting;
  11. Permitted FM ChannelsE when using the Freedom Speech processor: p16, FM Solutions for Cochlear Implants, Phonak.
  12. ANSI/ASA S12.60-2010 Standards on Classroom Acoustics Parts 1 & 2, available for free download at the Acoustical Society of America website store, courtesy of Armstrong;
  13. Johnson, Cheryl DeConde (March 2015). 20Q: Understanding and supporting reluctant users of remote microphone technology. AudiologyOnline, Article 13554.
  14. DOJ/OSEP. (November 12, 2014). Frequently asked questions on effective communication for students with hearing, vision, or speech disabilities in public elementary and secondary schools (PDF file);
  15. Johnson, Cheryl DeConde (2014). Important ADA Policy Guidance on Effective Communication. Educational Audiology Review (PDF file);

Bootnotes:

A: SINAD is “Signal In Noise And Distortion,” and is the mathematically correct way to refer to the ratio of desired to undesired components in an audio signal. SINAD is defined as:
   (Signal + Noise + Distortion)
        (Noise + Distortion)
…however when combined noise and distortion are only 1-2% then SINAD → S/N;

B: Note that the SINAD definition applies to audio circuits such as hearing aids and audio amplifiers, and does not really apply when there is a major time component in the system, such as what is referred to as “noise” that occurs from the room reverberations that mask speech formants — That’s a whole new ballgame and is beyond this article, except to say that this additional reverberant “noise” only strengthens the case that FM/RM be mandatory for all hearing impaired children;

Roger-1-and-2-text-2517-cropC: Phonak made a quiet but welcome running change in Spring 2014 when they switched to their second generation chip inside their Roger headworn receivers: Besides on a drain meter where you will see a drop in power consumption from 3.0 to 2.4 mA, you can tell them apart as on the X universal receivers they switched to cadmium plated pins as the brass plating on the original series would flake off, and possibly cause a short circuit. In addition, another welcome change is the new receivers boot up about 2 seconds faster, almost immediately;

D: We had the pleasure of meeting the passionate-but-pleasant Juliëtte Sterkens at #AN15 several weeks ago. She is a tireless advocate for communications access for the hearing impaired, and certainly worthy of the accolades and awards she has earned; and in fact we agree 95% with her, including on the need for a common standard of audio transmission to hearing aid and CI users. However, on her principled position on widespread baseband induction “hearing” loops, our differences are intractable; and on that sole technical point we “agreed to disagree;”

E: To avoid interference, the following analog FM channels are recommended by Phonak to be used with the MicroLink Freedom CI speech processor:
216 mHz N Band: N09, N12, N13, N16, N17, N18, N52, N57, N61, N62, N64, N65, N68, N73, N76
168 mHz H Band: H06, H07, H16, H17, H18, H19, H20, H47, H48, H57, H59, H77, H78, H79, H85, H86, H87, H88, H89, H90

F: On one major point we agree with the aforementioned Juliëtte Sterkens: The desperate need for a common industry standard for wireless direct-to-hearing aid and CI audio transmission, especially for public venues such as theaters, arenas, and houses of worship. On this point, the leadership of the Hearing Industries Ass’n trade group has been a miserable #FAIL, as although four of the “Big Six” manufacturers use the 10.6 mHz ISM band for their HIBAN networks between their dongles and hearing devices, each of these four have their own proprietary — hence incompatible — encoding and transmission protocols (and Starkey’s 900 mHz platform on some of their hearing aids is a fifth). Given that in 2014 fully 80% of the hearing aids dispensed in the US have wireless capabilities built in, this presents a miserable situation for the hearing impaired community. Post-Jobs Apple tried to bring the industry together with their “Made for iPhone” BT4 Low Energy (“BLE”) program, but so far only GN ReSound, Starkey and Cochlear have fully signed on. You can publicly register your complaint with HIA here;

University of North Texas Audiology Professor and Program Director Erin Schafer PhDG: We also have the pleasure of learning that our friend, the aforementioned Professor Erin Schafer PhD, is the new head of the audiology school at the University of North Texas; and we wish her all the best~

 

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About the author

Dan Schwartz

Electrical Engineer, via Georgia Tech

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