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Interview with Laurel Christensen, Ph.D., Vice President, Research and Development, GN ReSound Group

Laurel Christensen, PhD

September 28, 2009

Topic: Introducing ReSound Live™

Laurel Christensen, Ph.D.

CAROLYN SMAKA: I have the pleasure today of speaking with Laurel Christensen from ReSound. Welcome to AudiologyOnline.

LAUREL CHRISTENSEN: Thank you for having me.

SMAKA: Dr. Christensen, can you talk about your background and your current role at ReSound?

CHRISTENSEN: Sure. I've been an audiologist for 20 years which is hard to believe. My first clinical audiology job after receiving my master's degree from Indiana University in 1989 was working for an otologist in Indianapolis. I worked a few days a week while I pursued my Ph.D at the same time also at IU. After receiving my Ph.D, I became an Assistant Professor at LSU Medical Center in New Orleans as part of both the Department of Communication Disorders and Kresge Hearing Research Laboratory. During my time at LSUMC, I was fortunate to be invited to participate in some clinical trials of hearing aid technologies for several hearing aid manufacturers. Through this work, I developed a real interest in hearing aid development.

After seven years at LSUMC, I was given an opportunity to do a sabbatical at Etymotic Research (ER) in 1998, but decided instead to leave my job at LSUMC completely and go to work for ER full time. At ER, I was able to be a part of product development for several products. After five years at Etymotic, I was recruited by GN ReSound to start an audiology research team in the United States. I started out heading up a small team of audiologists in Chicago doing product verification and clinical trials. That grew into my current position in Research and Development (R&D), where I am in charge of both Audiology and Research. These teams combine with several others and make up the R&D function for GN ReSound Group. About two-thirds of our development is done in Europe, and the other one-third is done in the U.S., here in Chicago.

SMAKA: How long does product development typically take from the idea phase to the, okay, we're ready to launch it phase?

CHRISTENSEN: That's a good question. It completely depends upon whether or not your product is going to require a new chip and complete new functionality, or if the product will use an existing chip with added signal processing or new hardware.

For products that require a new chip, it's about a three-year period to develop the new DSP, the hybrid, mechanics, and software. A chip cycle will typically be several years, during which time new products will be developed on the same platform. For new products using an existing chip, the development time is approximately one year to lock in the specifications and do what's needed to develop the product.

SMAKA: That's a great segue into our topic today, which is a brand new product, ReSound Live™. How did this development come about?

CHRISTENSEN: ReSound Live™ is our complete new flagship product line. There are three different price points - Live 9, Live 7 and Live 5, all being introduced at the same time.

The Live™ introduction represents the culmination of several years of work that we have done to solve some end-user sound quality problems. In Sergei Kochkin's MarkeTrak VII (2005), the top factors related to end-user satisfaction with hearing instruments were outlined. In the article, Kochkin states, "Incremental improvements in these areas will drive improvements in overall user satisfaction." We looked at these factors, and while overall benefit was number one, we noticed that a number of factors related to sound quality - things such as sound clarity, sound richness, sound fidelity and naturalness of sound. In fact, upon further examination we found that three of the top ten factors were actually related to sound quality. People are looking for better sound quality than they currently have in their hearing aids today.

ReSound Live™ was designed to be a breakthrough in sound quality and an overall better hearing experience. We've included features to enhance the richness and fidelity of sound for the end user. In addition, we know how important hearing in noise is for end users. Kochkin (2005) indicates that the ability to hear in noise, as well as in small groups and leisure activities which are often noisy, is also among the top factors important to satisfaction. In the development of ReSound Live™, therefore, we take another step forward in providing the best hearing in noise possible. The product offers five microphone response options to provide maximum flexibility for the dispenser and end-user.

Lastly, Live™ was designed to be easy to use and comfortable. To that end, we're introducing an entirely new digital feedback suppression system in Live™ called Dual Stabilizer® II DFS with WhistleControl™. This feedback cancellation system is very effective at both increasing usable gain and reducing dynamic feedback, the kind that's caused by pulling on a hat, putting a telephone to the ear, or by movements near the hearing instrument at the ear.

SMAKA: The name Live evokes a performance, concert or event. Is that what you had in mind?

CHRISTENSEN: Yes, exactly. With the name Live, we wanted to evoke the idea of a state-of-the-art, surround-sound, theater-like experience, that speaks to the new fidelity offered by this product.

SMAKA: When I think about the sound quality of hearing instruments today as compared to when I started out in audiology over 15 years ago, the difference is unbelievable. But a person who has never listened to a hearing aid before has a very different perspective and expectation.

CHRISTENSEN: Good point. Also, if you consider some of the features over the years that have provided good end-user benefits, they've come with side effects that have negatively affected sound quality and thus might not have been used as often as needed.

For example, directional microphones provide a measurable end-user benefit when listening in backgrounds with noise, however, this hearing aid setting is inherently noisier. To reduce the internal noise in the instrument in the directional setting, the manufacturer most often introduces a low cut to the frequency response. Although the cut is effective at reducing the internal noise, the change in frequency response substantially changes both the overall quality of the sound and the gain in the low frequencies that is often required for people with low frequency hearing loss to understand speech.

Think about how you adjust your stereo system at home or how you would adjust an equalizer in front of you, where you have total control over treble and bass. If you were to listen to music, speech or other sounds and adjust the equalizer to where things sound best, you would not likely cut all of the bass response. Most people get the perception of a rich, full sound experience by increasing the low frequencies. So, traditional directional responses take away the rich, natural sound quality that end-users desire.

In ReSound Live™, we introduce a new sound package called Surround Sound by ReSound. This feature set includes Warp compression at its foundation;the surround sound processor, Dual Stabilizer® II DFS with WhistleControl™, NoiseTracker™ II, and the Environmental Optimizer™. At the heart of this feature set is the surround sound processor. This processor always maintains an omnidirectional response for the lowest frequencies. In a directional setting, the higher frequencies will have a directional response for good signal-to-noise ratio improvement. Thus, in the directional setting, the richness of sound that is so important to the overall listening experience is maintained.

SMAKA: What other features contribute to Live's™ high-fidelity and to improving hearing in noise?

CHRISTENSEN: As I mentioned earlier, one of the primary challenges of helping patients hear in noise is getting them to use a directional program. The lack of great sound quality and hassle of changing programs often diminish the benefit of sophisticated directional systems for patients. Surround Sound by ReSound eliminates this sound quality barrier to the use of directional programs by patients. No matter which directional option a professional chooses the Live instrument with Surround Sound Processing will offer superior sound quality.

The second component to offering better speech understanding in noise is the level of sophistication offered by the directional programs in an instrument. Live™ has several options for hearing in noise. No other hearing aid available has this many options. One of the options called Natural Directionality was originally introduced in our Azure™ hearing instrument. When listening in the Natural Directionality setting, the hearing instrument in one ear has an omnidirectional microphone response, while the other hearing instrument has a directional response. Using a setting like this has been shown to provide the same directional benefit in real world environments as using two hearing instruments in the directional setting. (To name a few of the research sites I would mention Ruth Bentler at University of Iowa, Jurgen Keisling at University ENT Clinic in Giessen, Germany, and also Brian Walden and Mary Cord at Walter Reed Army Medical Center.) There are many advantages to leaving one hearing instrument in the omnidirectional setting. The biggest advantage is not having to rely on the environmental steering or auto steering within the hearing instrument to switch the hearing instrument into a directional setting when necessary. Several studies have shown that these automatic hearing aids are often not in the setting the patient should be in for a given environment. In addition, it is impossible for the hearing instrument to know what the patient wants to listen to. This signal of interest may well be behind the person and if switched to directional in both hearing instruments there is no way for a user to hear this signal.

My own home is a perfect example. In my living room in the evening, there can be multiple speech signals and noise from every direction including a television, children and adult voices, computer game noise, toys that make noise, and even a toddler who can be talking, screaming, or crying at any given moment. There is no way a hearing instrument can determine what I need or want to hear. I need to be able to hear everything even though I may not want to. The same is true for someone with a hearing instrument - limiting them to a narrow cone or tunnel of hearing to the front does not allow them to listen to their environment in a normal manner.

Our philosophy at ReSound is to give patients access to the acoustic information which will allow them to orient themselves in the environment. No hearing instrument intelligence is anywhere near as sophisticated as the brain in integrating this information to form an understanding of the listening environment. The ability to hear what's going on all around you and form a picture of your environment is what allows you to decide where to place your attention and to focus on that. Knowing where to direct your attention actually makes listening in noise an easier task. We equate this to giving patients a complete surround sound experience - because they are not cut off from the sounds occurring around them and because of the way the sound is processed, they get a natural-sounding experience that allows them to choose what they're going to listen to. At ReSound, we don't want to put a patient in a tunnel because we know there are things outside of the tunnel that the patient may want or need to hear. When patients can hear everything, they can decide where to direct their attention, and that's the idea behind Natural Directionality.

With Live™, we've taken Natural Directionality a bit further. As I mentioned, Live's™ surround sound processor provides split band directionality with omnidirectional always maintained in the low frequencies, and in a directional setting, a directional response in the high frequencies. Live's™ directionality, due to the new surround sound processor is completely transparent across the two hearing aids. There's no way that the end user would know that one hearing aid is in a directional setting, and the other is in omni. We call this Natural Directionality II and it really enhances both directionality and the overall listening experience.

SMAKA: When I first saw Natural Directionality on Azure, I was thinking, "This is a whole new direction from where other manufacturers seem to be going with directional."

CHRISTENSEN: Yes, when we came out with Natural Directionality, we were kind of going against the grain. Directional microphones had been out for a very long time, and satisfaction rates are higher for people who have hearing aids with directional mics. But we were basically saying, oh, but you don't really need two hearing aids set to directional;you only need one. Beneficial features in hearing aids often come with undesirable side effects when patients use them. For directionality this side effect really is the tunnel hearing and the inability of the hearing aid to really know what the patient is listening for.

The message is simple in Natural Directionality;we want to keep people listening as they listened before they had hearing aids, with the ability to hear things from all around them. Patients do better in real life if they can listen to what's around them and also get the benefit of the directionality from one hearing aid set to directional.

SMAKA: That's a really good point. We tell people with directional hearing aids to make sure that you face what you want to listen to. But as you know when you have kids, you really need to be listening for them when they're not facing you, because that's when they're up to something. [laughs]

CHRISTENSEN: [laughs]. True - it's hard to face what you want to listen to when you don't even know its happening because it's behind you. Unfortunately, that's often the case with traditional dual, directional settings that reduce sounds from behind you.

SMAKA: Dr. Christensen, you mentioned that ReSound Live™ was designed to be easy-to-use and comfortable. We know these factors are critical to a hearing aid fitting - what does Live™ bring to the table?

CHRISTENSEN: Let's talk about the new feedback control system called Dual Stabilizer® II DFS with WhistleControl™. ReSoundAIR set the standard in terms of ease of use and comfort, and there is no doubt that ReSound has since been the leader with what we would call "static gain" due to a feedback suppression system. We had the very first feedback cancellation system where we actually cancel the feedback, not reduce gain, but true feedback cancellation. We have never lost the leadership position of providing the most additional static gain in our hearing aids with the feedback system on.

SMAKA: Can you explain static gain?

CHRISTENSEN: Sure. Static gain is easy to measure in the clinic. For example, fit a completely open hearing aid on a patient and turn the feedback system off. Then, increase the gain in the high frequencies until the hearing aid feeds back and note how much gain was needed for this to occur. Now you have one set of gain numbers probably averaging around 15 dB, because that's about the most gain you can get in the high frequencies in a completely open hearing aid without a feedback system. Then, turn the feedback system on, and increase the gain again until the hearing aid feeds back. The difference between the gain needed to achieve feedback with the feedback system on vs off is what we call "headroom" or "static gain." It is the additional gain provided because the feedback management system is active.

Even if the system does well in terms of this "static" feedback, the ability to handle dynamic feedback that is caused by putting something like a hat on your head or putting a phone up to your ear, though, is a totally different kind of feedback animal. Some feedback cancellation systems adapt pretty well to these kinds of changes but the downside is that they also attack sounds that are not feedback, like microwave beeps or keys jangling or even finger-snapping. This creates distorted ringing and chirping sounds that can be very annoying for the user. This is why some manufacturers have "music" settings for their feedback cancellation systems where they slow down the adaptation to try and prevent it from interfering with the music. The ReSound system also adapts but we actually limit the amount of adaptation in order to make the system not react to environmental non-feedback sounds, which vastly improves the sound quality over a system that adapts no matter what. Again, there's often a downside, and for our system it is that feedback may not always be cancelled in extreme situations where the feedback path changes a lot, like when holding a phone up to the hearing instrument.

In Live™, we wanted to add a dynamic feedback system to reduce feedback in these extreme kinds of situations, while maintaining the good static gain and excellent sound quality that we have always provided. We did this without compromising or taking anything away. In hearing aids from other manufacturers, it can be one or the other;you might get good static gain but without the dynamic system turned on at that same time. With Live™, we are introducing a Whistle Control feature for dynamic feedback. When a whistle is detected in the instrument, it takes the whistle out, and restores the gain in the hearing aid to the gain prescription.

If you think about how the feedback loop is continually amplifying and that's what causes feedback, essentially Whistle Control stops that crazy loop and takes the gain to the level that it should have been before. If you watch it in real time with a probe mic system, you can see the feedback peak come up, and then disappear as the original frequency response is restored. It's a great system for controlling the whistle without losing gain, and without compromising the sound quality of the hearing aid.

SMAKA: You mentioned ReSound Live™ is not a product;it's a product line. What's the difference between Live 9, 7 and 5?

CHRISTENSEN: The flagship product is ReSound Live 9, which has all the features we've been discussing.

In addition to being fully-featured, Live 9 is an extremely flexible system. For example, with Live 9, the dispenser can control the "directional mix" of the product. The directional mix determines the frequency where omni processing is occurring below and directional processing is occurring above this frequency. In addition to full control over the surround sound processor, Live 9 includes Natural Directionality II, all of the Whistle Control features, as well as NoiseTracker II, and the Environmental Optimizer. Although we are obviously big believers in the benefits of Natural Directionality, if there's a patient out there who for some reason really wants a dual directional setting, you can give them that. There is also the option of setting up an adaptive directional system. Live™ also includes a unique feature called Autoscope, which will automatically widen or narrow the width of the beam of the directional system based on an analysis of where the signal of interest is coming from. Even with a bilateral directional setting, the end-user is going to have more access to environmental sounds occuring outside the directional beam because of the omnidirectional processing in the low frequencies. Like I've said before no one offers more directional settings.

Live 7 and Live 5 include a sub-set of features of Live 9. It's a matter of determining which is best for each patient, depending on the number and type of listening environments they are in. For best performance in all environments, Live 9 is recommended, but Live 5 still has a pretty impressive feature set for a more budget-oriented hearing aid.

SMAKA: What models or form factors are available with Live™?

CHRISTENSEN: Live 9, Live 7 and Live 5 all encompass a full product line from CICs to power BTEs. They also include our remote microphone products, the new form factor where we've taken the microphone out of the case.

You can think of the remote microphone products as being similar to a CIC where the microphone is moved out of the case and placed up in the concha of the ear. Because the microphone is moved out of the case, these instruments can be made smaller, or with a much, much larger vent, to accommodate as open a fitting as possible with a CIC form factor. Another advantage is that the microphone is in a location where it is not exposed to wind at all, so there are no wind noise issues with this form factor. This is a benefit for patients who sail, golf, cycle, or participate in any kind of outdoor activity where wind noise would be a problem with other hearing aids.

The Live™ product line also includes a new receiver in the ear model. It's a very nice cosmetic form factor for patients who want a very small BTE and receiver in the ear.

SMAKA: "Live 5 with ReSound Surround Sound" should be a new rap song, I'm loving the rhyme. You guys should see if you could get that going to promote the product. [laughs]

CHRISTENSEN: [laughs]. I'll see what I can do!

SMAKA: You can see why I'm not in marketing. When will Live™ instruments be available for order?

CHRISTENSEN: The official launch is early October. At the very same time, we're launching a new version of our very, very popular dot product, called dot² by ReSound®. This product also includes Surround Sound by ReSound and is a multi-program version of our popular dot by Resound®.

SMAKA: Wow, you are busy, that's a lot of new products all at once.

CHRISTENSEN: We are definitely busy. But the great thing is it is actually very simple. All six new products are based on the same technology.

SMAKA: Thank you for your time, Dr. Christensen, and wishing you much success with all the new developments.

CHRISTENSEN: Thank you, Carolyn.


Kochkin, S. (2005). MarkeTrak VII: Customer satisfaction with hearing instruments in the digital age. Hearing Journal, 9, 30-43.

About ReSound

ReSound develops technology and solutions to improve quality of life for hearing impaired throughout the world. Founded in 1999 through a merger of GN Danavox and ReSound Corporation combining 90 years of hearing instrument development, ReSound today upholds its illustrious history as a leading manufacturer of cutting-edge hearing instruments in major global markets. ReSound North America is headquartered in Bloomington, MN. For more information, visit, or the ReSound web channel on Audiology Online.
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laurel christensen

Laurel Christensen, PhD

Chief Audiology Officer for GN ReSound Group

Laurel A. Christensen, Ph.D. is the Chief Audiology Officer for GN ReSound Group. In this role she leads a global team of 26 audiologists that are responsible for all aspects of audiology for the company including new product trials, audiology input to marketing, and global audiology relations which encompasses training and product support to subsidiaries world-wide. Prior to joining GN ReSound, she was a researcher and Director of Sales and Marketing at Etymotic Research in Elk Grove Village, IL. While at Etymotic, she was part of the development team for the D-MIC, the Digi-K, and the ERO-SCAN (otoacoustic emissions test system). Prior to this position, she was a tenured Associate Professor on the faculty at Louisiana State University Medical Center and part of the Kresge Hearing Research Laboratory in New Orleans, LA. During this time at LSUMC, she had multiple grants and contracts to do research including hearing aid regulatory research. In addition to her position at GN ReSound, she holds adjunct faculty appointments at Northwestern and Rush Universities. She served as an Associate Editor for both Trends in Amplification and the Journal of Speech and Hearing Research. Currently, she is on the board of the American Auditory Society and is a member of the advisory board for the Au.D. program at Rush University. Christensen received her Master’s degree in clinical audiology in 1989 and her Ph.D. in audiology in 1992, both from Indiana University.

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