Inside the Research | September 2017 Hearing Review
Ted Venema, PhD, has been a well-known author and educator for over 20 years and recently released the third edition of his book, Compression For Clinicians: A Compass for Hearing Aid Fittings (Plural Publishing).1 We thought this would be a good opportunity to revisit some of the topics surrounding this constantly evolving area.
Beck: Hi Ted. Great to speak with you again and congratulations on your latest book. I have to say, the book gets better with each edition and I can hardly wait to read the 5th edition!
Venema: Thanks Doug. Well, the third edition was published by Plural Publishing and I know you know that group very well. They are fabulous…but the third may be the final edition. Then again, never say never.
Beck: Fair enough. For the few people in our profession who may not be familiar with you, please briefly review your professional history.
Venema: I earned a BA in Philosophy from Calvin College in Grand Rapids, Mich, and had never heard of audiology. Years later, my friend at the time (my spouse, now) suggested I become a speech therapist. I enrolled at Western Washington University in Bellingham, Wash, and like many speech students, I ended up taking a lateral shift sideways and earned an MA in audiology. I worked as a clinical audiologist at the Canadian Hearing Society in Toronto for 3 years, but always knew I wanted to go on for further studies. I earned my PhD in 1993 from the University of Oklahoma. I taught at Auburn University for 2 years, and then moved back to Canada and worked at Unitron for 6 years. After that, I was an assistant professor at Western University in London, Ontario, for another 5 or 6 years. In fact, I think I met you while I was teaching there? I think we may have both been speaking at the same venue…Nonetheless, after teaching there, I started a 2-year Hearing Instrument Specialist program at Conestoga College in Kitchener, Ontario, and I taught there for about 7 years. After that, my girlfriend (now my wife) and I moved to the Western side of Canada and now live in Victoria, BC, Canada, also known as the “wet coast.” Currently, I teach online courses for Ozarks Technical Community College in Missouri in their hearing instrument program.
Beck: Excellent! Which classes are you teaching?
Venema: This past year I taught Acoustics, and as you might have guessed I also taught Compression, Real-ear Measurement, and I teach Hearing Disorders. It varies semester by semester, based on what they need, but it’s a real joy for me and the students are fantastic.
Beck: I should note that your book addresses other topics beyond compression. For example, it starts with “Common Clinical Encounters: Do We Really Know Them?”; proceeds through the topics of inner and outer hair cell damage and cochlear dead zones; reviews the ideas behind both old and new concepts in fitting methods and algorithms; delves into some of the finer points of verification, and tackles the topics of compression in the DSL and NAL fitting methods. It then brings the reader into a comprehensive look at compression in analog and digital aids—as well as compression with directional microphones and more advanced features like digital noise reduction and adaptive dynamic compression. So clearly, the book offers quite a bit more than a contemporary view on compression.
Venema: Thanks for mentioning that! Throughout the book, I try to separately address the ideas and concepts of “sensory” (as in outer hair cell issues) versus “neural” (as in inner hair cell issues). Because, as you know, Doug, there is a world of difference between the two, yet we tend to minimize those differences when we use terms like “sensorineural hearing loss” or “SNHL.”
Beck: So let’s talk a little about inner versus outer hair cell issues. Outer hair cell (OHC) loss is a sensory loss, and it’s the most common type of damage to the auditory system, resulting in a mild-to-moderate degree of hearing loss. OHC damage comes about most often from presbycusis and noise-induced hearing loss, and these are comparatively simple problems to address with amplification, as the patient needs audibility (the ability to perceive all the speech sounds) and an improved signal-to-noise ratio (SNR) to help them focus on the sounds of maximal interest. In general, people with mild OHC loss have decent-to-excellent word recognition and usually a mild-to-moderate high frequency SNHL—and that’s pretty straightforward.
Venema: Right! In contrast, inner hair cell (IHC) loss is a whole different kettle of fish. IHC loss usually tends to follow OHC loss, so it’s usually associated with a more severe degree of hearing loss. With IHC loss, one’s speech discrimination ability becomes more severely compromised. Of note, OHC loss and IHC loss are best respectively served by Wide Dynamic Range Compression (WDRC) and Output Limiting Compression (OLC). WDRC was designed to roughly imitate the OHCs: it amplifies soft sounds a lot, and loud sounds by little or nothing at all. OLC provides lots of gain for soft and average inputs and suddenly slams on the brakes for loud inputs.
Another distinction is the necessity for hearing aids to provide not only gain, but also an improved signal-to-noise ratio (SNR). An improved SNR is especially necessary for those with severe hearing loss due to IHC loss. Again you need audibility, but now the hearing loss severity and damage is more significant, and the hearing loss might be moderate-to-severe-to-profound—where simply making it louder is not going to satisfy these people; they also crave clarity!
Beck: That reminds me of the guidelines Harvey Dillion wrote about when he suggested that, for every 10 dB of hearing loss (based on a 4 frequency pure-tone average), we need to improve the SNR by 3 dB just to maintain the intelligibility the person has unaided. So for example, if someone has a flat 65 dB loss, and given that 0-25 dB is considered “normal hearing” for adults, that same person has 40 dB of hearing loss, and so they would require a 12 dB improvement in the SNR.
Venema: That makes perfect sense and I agree. And, of course, those are the goals of modern hearing aids: to make sounds audible and to improve the SNR. I think one has to pay attention to the words of Mead Killion, PhD, from some years back when he reported the problem with IHC loss is the fact that you have a garbled signal traveling from the ear to the brain, and so the brain has to work significantly harder to make sense of the sound.
Here’s another interesting clinical twist: because the degree of hearing loss is more significant for people with IHC loss—perhaps 70 dB or worse—they are often easier to fit with hearing aids! That is, without hearing aids, it can be extremely difficult for them to hear conversational speech at all. Amplification allows them to participate, to achieve audibility—although admittedly, the whole experience is still very difficult—as their own internal auditory system prevents them from hearing clearly.
Beck: So you’re saying that regarding hearing aids for this population, the “glass is half full?”
Venema: Exactly. They can achieve audibility with powerful, but usually less expensive hearing aids, with fewer bells & whistles, because they may not be able to perceive the automatic processing ability of sophisticated amplification. The mild-to-moderate hearing loss population—those who can still hear without their hearing aids—are ironically the clients who are often more difficult to fit!
Beck: And so that may take us to a brief discussion of digital noise reduction (DNR). I often argue that DNR is just about the worst name for circuit ever devised, as it hardly reduces noise—unless the noise is a steady state like a HVAC system, the humming of a refrigerator, motor noise, etc. However the most difficult noise of all time, which we all want reduced, is the dynamic sound of other people talking while we’re trying to listen to a particular person.
Venema: Thanks for saying “digital noise reduction” and not “digital noise removal.” That’s a very important difference. We’re on the same page on that one! The assumption made about noise is that its intensity is relatively steady over time, much like that of a fan or an air conditioner. On the other hand, the intensity of speech spoken close up is “staccato,” with lots of starts and stops; it fluctuates wildly over time. Even the “hubbub” and “babble” of background speech is more steady in intensity over time compared to that for close-up speech.
Trouble is, when the DNR in a multi-channel hearing aid senses steady-state noise in any of its channels, the gain in those channels is reduced for both the speech and the noise in those channels! So the real challenge for DNR is not a matter of improving speech understanding in noise; rather, it is to ruin the understanding of speech as little as possible, or mitigate its impact upon speech!
And so in 2017 and moving forward, to objectively help people hear better in noise, it’s our obligation to improve their Speech in Noise (SIN) score. We should evaluate their SIN score, and arguably our primary goal should be to improve their SIN score.
Beck: Absolutely. I’ve been saying the most-important measure we can obtain is the SIN. And, to be frank, it only takes 3 to 5 minutes, and makes all the difference in the world. It’s surprising to realize that the single most-common complaint of people with hearing loss and people wearing hearing aids is understanding speech in noise, yet fewer than 20% of all hearing care professionals measure it.
To me, it’s a simple and easy measure to obtain, and it is the only way to document the patient’s experience, and their primary complaint. The goal then becomes improving their ability to understand SIN. And here’s some tough love: if the hearing aids have not improved their SIN, it may be a failed fitting!
Venema: I couldn’t agree more. HCPs and clients need to understand that, when you’re 1-3 meters away from people speaking, most hearing aid circuits will recognize the speech sounds are highly dynamic and DNR will not be able to do much! When you’re much farther away, like 7-10 meters from a group of people speaking at a dinner table, the same people speaking may sound more steady-state-ish, and perhaps the DNR will be more useful as the “once-dynamic sound” approaches a more “steady-state” presentation, such as hub-bub and babble. Yet, there is a trade-off: as the DNR becomes active in the lower frequency channels, it does take away some “noise” which is really speech. So, in those situations, some low and mid-frequency speech sounds may actually be attenuated.
That said, here’s something to consider however, about DNR—and I wrote about that in Chapter 9 of the book which looks at the clinical benefits of DNR to those of directional microphones. The one good thing about DNR is that, subjectively, it may enhance the listening comfort in noisy environments. This may have a significant contribution to the hearing aid fitting: namely, the client may end up wearing the hearing aids more often!
Beck: Of course, the other technology often used to reduce background noise is directional mics. And, although the directivity index may indicate a 4, 5, or 6 dB directional microphone advantage, that number results from a manikin in an anechoic chamber listening to pure-tones in relative silence. In the real-world, although certainly beneficial, I suspect the actual benefit is closer to 1 to 2 dB. Your thoughts?
Venema: I think that’s correct. And of note, even the very best directional mic system is considerably less effective than its specification sheet indicates, given an open-canal or open-ear fitting, as lots of noise comes into the ear canal without going through the hearing aid. Still, it should be said that even a few dB improvement in SNR can lead to an objective improvement in listening performance in noise. To that end, directional mics have their definite role.
Beck: So before I let you run, tell me your thoughts on real-ear measurements (REMs): where we are and do they really matter?
Venema: Ahhhh. I was hoping you’d ask! First, I’ll refer to your new article2 on automated REMs published in the April Hearing Review, along with your interview last month in this column with Gus Mueller.3 The simple facts are that, in 2017, speed and accuracy matter—and REMs matter, too! So, if we can accomplish REM measures through the hearing aid, fantastic! If not, the primary measures which seem to matter in 2017 are real-ear aided responses (REARs), which are more-or-less the measurement of sound with the hearing aids in place (in-situ) and turned on. I think it’s important to gather REARs on every fitting so we have verification of the actual sound—the aided “groceries” if you will—being delivered to the client’s ear-drum. It’s well known that, without measuring the sound between the hearing aid and the ear drum, we are truly operating in the dark. We know with certainty that a true estimate of aided outputs cannot be determined via first fittings. I mean, asking the patient “How does that sound?” only goes so far!
Beck: And rather than going into a discussion of how to do REMs, I loved what you wrote on page 160 about why to acquire REMs. So please give us an abstract here, and perhaps embellish it a bit!
Venema: OK, let’s do it. I wrote in the new book (and I actually got much of it from Adam Perrie, an HCP I know in Ontario, Canada) about some common objections to doing REMs, along with some snappy answers…
Statement #1: REM equipment is too expensive.
Response #1: It starts at few thousand dollars, a profit you’ll make on the sale of a few hearing aids!
Statement #2: I don’t have to.
Response #2: Look closely at your bylaws; it’s rapidly becoming “best practice.”
Statement #3: (From a non-audiologist HCP) Audiologists don’t have to.
Response #3: Imagine offering better service than them.
Statement #4: I prefer client satisfaction scales.
Response #4: How this trumps objective measures is a true mystery.
Statement #5: My competition doesn’t bother, why should I?
Response #5: God forbid you should offer better service than the competition.
Statement #6: The software already does the work.
Response #6: Read the book again!
Beck: Thanks Ted. I greatly enjoyed the discussion, and I totally applaud and endorse the book—I believe it should be required reading for all HCPs.
Venema: Thanks Doug. Very best wishes and I’ll see you on the lecture circuit!
1. Venema TH. Compression for Clinicians: A Compass for Hearing Aid Fittings. 3rd ed. San Diego: Plural Publishing;2017.
2. Beck DL, Crowe N. Easy, fast, and accurate: Hearing aid fittings via an automated REM system using IMC 2. Hearing Review. 2017;24(4):30-31.
3. Beck DL, Mueller HG. Speech mapping and probe microphone measurements: An interview with Gus Mueller, PhD. Hearing Review. 2017;24(7):38-39.