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

Laurel Christensen, PhD

June 6, 2005
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Topic: Metrix - Amplification Technology from GN ReSound
Beck: Good morning Laurel, thanks for joining me today.

Christensen: Hi Doug. Nice to be here.

Beck: Laurel, although I'd like to focus our discussion on the new Metrix product from GN ReSound. However, if you don't mind, would you please tell me a little about your professional background first?

Christensen: Absolutely. I earned my master's in 1989 from Indiana University and my doctorate three years later, also from Indiana University. My doctoral dissertation was related to that and had to do with speech understanding and aging and this continues to be my main research focus. After graduation, I went to Louisiana State University Medical Center in New Orleans and I was on the faculty in the School of for Allied Health and Kresge Hearing Research Laboratory. After 7 years in New Orleans, I left the university and joined Etymotic Research in Illinois. I was the Director of Sales and Marketing at Etymotic. I joined GN ReSound two and a half years ago. I have a team of 176 audiologists, and we do basic and developmental research and clinical trials in both Chicago and also Copenhagen.

Beck: Very good. Thanks Laurel. Please tell me about the Metrix?

Christensen: The Metrix is our newest hearing aid. It was officially launched just a few weeks ago, May 16, 2005. The Metrix is our newest, most sophisticated, high-end product.

Beck: How did GNR go about designing the Metrix? What was the goal?

Christensen: The goal was to solve the real, day-to-day end user problems. For example, we wanted to address poor maximize sound quality issues, difficulty hearing in noise problems and fitting accuracy. We also wanted to continue to lead the industry in and we wanted to have occlusion free fittings. This product contains major advancements in adaptive directionality and noise reduction. Other major issues for us were adaptive directionality and noise reduction...and this product just does a superb job of handling these issues. Everything in the Metrix is new. The platform and the Coyote III chip, hardware and fitting software were developed together for this product chip are all new, and they're in all new hardware and a completely new fitting software program, too.

Beck: OK -- Let's talk about some of the specific parameters of the Metrix...How about if we start with noise reduction? What sort of noise reduction program is used?

Christensen: The noise reduction program is an "industry first." Rather than using standard modulation detection techniques, which are common in the industry, we use a spectral subtraction method. For example, imagine a spectral picture of noise and a spectral picture of speech. Then, combine the pictures to create a total sound picture of speech and noise, and then lastly, if attenuate the noise,
you're left with just the speech.

Beck: That sounds simple when you present it in those terms, but I'm sure accomplishing that subtraction in real-time is rather intense!

Christensen: Yes, it is. In spectral subtraction, we estimate the noise when there is no speech signal present. Based on this noise estimate, we then calculate a gain for both the signal and noise together that will make the envelope of the signal resemble a signal with less noise but the same amount of speech signal. Many of the competitive systems remove too many high frequency sounds and the end-user experiences a rather dull, muted sound. Of course, we cannot remove all the noise, nor would that be desirable, as eliminating all of the noise would make the sound artificial and could be disorienting for the user. And often, you know the "noise" some patients complain about, is often speech sounds they don't want to hear....but as we apply this technology across the 17 bands, it makes an enormous difference, and importantly, it doesn't remove speech sounds...speech integrity is maintained, while the majority noise is removed.

Beck: What about directionality?

Christensen: The directional system in the Metrix is adaptive dynamic, and works independently in each of the 17 bands effectively to attenuate multiple frequency noise sources originating at different locations.

Beck: So if a given sound of frequency X comes from one direction, while a different sound of frequency Y comes from another location, the hearing aid has the ability to attenuate both sounds?

Christensen: Yes, both sounds can be attenuated at once.

Beck: So in a cocktail party scenario, this is going to be a busy hearing aid circuit!

Christnsen: Yes, in that situation Metrix will constantly and instantly analyze the ever-changing acoustic environment to maximize the perception of conversational speech across all the bands, by evaluating multiple locations of multiple noise sources, across 17 bands in real time.

Beck: How would the Metrix know which speech sound to attend to, and which sound to attenuate?

Christensen: In our directional system, we assumes that the signal of interest is in the front. We have a very sophisticated chip that finely focuses on sounds originating in front of the listener, as you're most likely to want to attend to sounds exactly in front of you. We steer the front lobe of the directional pattern, to focus more towards the exact front of the listener than any other instrument on the market. Typically, in most directional hearing aids, the directional front lobe is off center a little, not at the true zero azimuth. In the Metrix, we've changed that by steering it back to zero, and we pick up an extra dB or two -- and that matters. Typical competing frontal lobes can be 70 to 80 or 90 degrees across the front....our lobe is much narrower, perhaps 40 or 45 degrees, depending on the frequency, so it is very narrow and focused, to better capture speech coming from the front of the wearer.

Beck: Excellent point. What about directionality in the ITC version as compared to the BTE?

Christensen: The ITC version has directionality and the DI is good, but the full shell ITE or BTE maximizes directionality and produces an increase of some 40 to 50 percent of intelligibility in noise.

Beck: That's very impressive. Is there a user controlled VC available on the Metrix instruments?

Christensen: Yes.

Beck: What can you tell me about "wind noise" reduction in the Metrix?

Christensen: Yes, we have a wind noise reduction system available too.The Metrix can handle wind noise within its directional system. It's built into the directional microphones and software and is easily managed.

Beck: Please tell me a little about the Metrix digital feedback suppression?

Christensen: This is our 5th generation of digital feedback suppression, so we've been producing these systems and improving them for a long time. One question that comes up with feedback suppression is headroom, and that's important,. Another and equally important issue is the sound quality which is often compromised when digital feedback suppression is working. So, we've addressed these issues, and importantly, the new digital feedback suppression is available works equally well in the omni directional system and in the directional response, which is unique compared to other multi-channel adaptive directional systems. and due to exclusive features of our system such as the calibration and adaptation filter constraints, we suppress feedback without compromising sound quality, while maintaining headroom. In other words, we don't reduce gain while engaging feedback reduction. Rather, we introduce an equal and opposite signal, allowing us to eliminate feedback without sacrificing headroom or sound quality.

Beck: Laurel two more topics before I let you run...Would you please address the multimedia fitting system, which I think is really very important, and would you also tell me about the data logging function of the Metrix?

Christensen: Sure Doug...The RAVE is a multimedia fitting system and it really is an impressive fitting system. It has 250 sounds including surround sound environments played and plays them through a five speaker system...but yet it's very easy to set-up, and does a good job simulating "real-world" environments. You can present all the sounds the patient might be exposed to throughout their day. It also includes a hearing loss simulator for counseling significant others. It really is a great fitting system.

Regarding data logging, as you know this is an old idea that has become popular again. It's built into the Metrix and allows the professional to get a clear picture of how the hearing aid has been used. It tracks things like how see how many hours the aid has been worn, the what sound environments the instruments were worn in, the programs and volume control settings and other features, too. The volume controls, and importantly, it makes suggestions based on the wearer's actual use, as to how to better program the device for that individual.

Beck: Thanks so much Laurel. The new Metrix sounds very exciting, and I'm
very appreciative of your time.

Christensen: My pleasure Doug.

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For more information on GN ReSound, visit the GN ReSound website.

For more information on Metrix, CLICK HERE.





NEW 4-part series presented in partnership with the National Acoustics Lab | October 5, 12, 19, + 26 | 5:00 pm EDT | Course Typ


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.