Frequently Asked Questions About SoundRecover
Carolyn Smaka: Great to speak with you again, Christine. You recently authored an article, Sound Bytes on SoundRecover, that has been very popular, and I thought it would be great to provide a summary of a few of the key topics here today. Can you provide an overview or definition for those who haven’t used SoundRecover?
Christine Jones: SoundRecover, generically known as non-linear frequency compression, is a form of frequency lowering that is applied in hearing instruments to improve access to high frequency information. It was developed in response to the necessity to deliver high frequency information that is critical for speech understanding, along with the technical challenges of doing that. The bandwidth of modern hearing aids may be insufficient for a number of reasons: hearing loss tends to be the worst in the high-frequency region; ear-level hearing instruments have technological limits when it comes to high-frequency output; feedback can be a limiting factor with increasing high-frequency gain; and high-frequency consonants, critical for speech understanding, are some of the softest parts of speech. SoundRecover is a technology that gradually applies some shifting and lowering to just the highest frequencies in order to move them to a space where those sounds may be more audible, hearing may be a little better, and more gain is available.
Carolyn: Who are candidates for SoundRecover from an audiological standpoint, and can this technology be used for both children and adults?
Christine: The evidence that we have so far indicates that both children and adults are candidates for SoundRecover. Compared to adults, children typically show more benefit (Glista et al., 2009) and adapt quickly. We know that audibility for high frequency consonants is extremely important during the critical speech and language learning window. The more severe the hearing loss is in the high frequencies, the greater the likelihood that high frequency consonants may be inaudible with conventional processing, and this is when SoundRecover really becomes beneficial. However, there have been studies that show that for very high frequency female /s/ sounds that peak at about 9kHz, even subjects with mild hearing loss can obtain some benefit from SoundRecover. In terms of adults, there are multiple studies that have shown benefit with adults from mild to severe hearing loss. Many of these studies are listed in the references of my recent article.
Carolyn: That leads me to another question. Who would not be a candidate for SoundRecover?
Christine: We want to apply SoundRecover when benefit or additional audibility is realized. Since SoundRecover is a form of compression, there is the potential for altering signal quality, so if you cannot derive benefit, there would not be a reason to turn it on. This can happen, for example, in patients with a reverse slope hearing loss, where hearing returns to normal in the high frequencies. It could also happen in the case of a corner audiogram, which requires the compression thresholds to be set below 2 kHz. I have seen patients who benefit from SoundRecover with that kind of audiogram, but I have also seen patients where this very aggressive setting results in consonant confusion and disruption of some of the vowel formants. For those conditions, I would be very cautious. On the other side of the spectrum, if you have a patient whose audiogram is such that you can achieve full audibility for speech in the high frequencies without SoundRecover, then it would be best not to apply it.
Carolyn: You mentioned that SoundRecover is a form of compression. Is there an acclimatization period, i.e., does it take patients a while to get used to SoundRecover?
Christine: Acclimatization is a topic that we are still learning about when it comes to SoundRecover. Studies with children have shown that there tends to be measurable benefit immediately after SoundRecover has been applied, when it is applied for the right candidates and fitted appropriately. Jace Wolfe and colleagues (2011) conducted a study with a group of children with moderate to moderately-severe hearing loss, who did benefit immediately from SoundRecover in quiet, but did not show immediate benefit in noise. They were retested six months later and some benefit in noise was measured, suggesting there was an acclimatization effect. Danielle Glista’s work on the acclimatization period for adults has shown that there is not one predictable pathway of learning or acclimatization for all patients. She studied a time course of 38 weeks in total. Some patients initially benefitted and then plateaued, where no additional benefit was realized over time. Some patients took a little bit of time in order to achieve maximum benefit. Then there were even patients who initially showed a decrement with SoundRecover because they needed to relearn some of the sounds they hadn’t heard and attach meaning to them. It is not predictable how an individual patient will benefit from SoundRecover; patients may differ in how they respond to it initially and then how they learn to best use it over time.
Carolyn: That is not a convenient answer for us but it does make sense when you think of individual variability with hearing aid benefit in general. Are there things that we can do to help people along with SoundRecover, such as auditory training or counseling?
Christine: That is a good question. There has not been any formal work done in this area to determine if a certain curriculum or auditory training tool will expedite the acclimatization period or optimize benefit with SoundRecover. However, adults that I have talked to have expressed the importance of tuning into the new sounds that they hear with SoundRecover right away. Many have told me that it has been helpful to have family members assist them in attaching meaning to the new sounds right from the start. When you start to hear sounds that you have not heard for many years, it can unclear as to what those sounds are. Are they sounds that you should pay attention to or not?
One woman told me that shortly after being fitted with SoundRecover, she was cooking in her kitchen and the smoke alarm sounded. She had no idea what that sound was, and so I think that counseling both patients and supportive family members to the kinds of high frequency environmental sounds that may become audible for the patient is important. Examples of these sounds may include signals and alerts from the car, from the microwave, sounds that food makes when it is being cooked, and certainly important alerting signals from fire and smoke detectors. The faster someone can understand what those sounds mean in the environment, the faster they will achieve benefit as well as comfort and connection to the acoustic world around them.
It is probably even more dramatic with children who may have never heard some of the sounds they may hear with SoundRecover. It is important for parents, when they suspect that there is a signal or a sound that might be new to the child, to stop and alert the child to that sound, and try to help the child assign meaning to new sounds in their environment.
Carolyn: Could you fit SoundRecover in cases where there is an asymmetric or unilateral hearing loss?
Christine: Let’s start with asymmetric hearing first. In that case, there is not strong evidence in the literature for how to fit those losses with amplification in general. The Phonak Target software by default will base SoundRecover parameters on the hearing in the better ear of a bilateral fitting, which means it could somewhat underfit the poorer ear. Some clinicians optimize SoundRecover settings in each ear individually as you would for gain and amplitude compression, and other clinicians maintain the defaults based on the better ear. There is no right answer as yet. Jace Wolfe (submitted, 2013) investigated this and did not find a difference between patients who were fitted to the better ear and patients who were optimized for each ear individually, but that may not necessarily be the final answer. Other researchers have started investigating this topic, so we look forward to further insight in the future.
In terms of unilateral hearing loss, there is no evidence from the literature right now regarding the use of SoundRecover for unilateral fittings. Anecdotally, we know of patients who have been successfully fitted unilaterally with SoundRecover.
Carolyn: You mentioned earlier about when SoundRecover is “fitted appropriately”. What does it mean that SoundRecover is fitted appropriately, and how do we verify it?
Christine: With SoundRecover, the recommendation is that you use just enough of it to achieve your desired level of audibility and no more. One of the best tools for assessing whether you need SoundRecover and how much, is electroacoustic verification. The procedure would start with meeting prescriptive targets across as broad a bandwidth as possible with frequency lowering turned off. Then, assess the patient’s access to high frequency stimuli. You can use various tools in real-ear systems to assess whether sounds like /s/ and /sh/ are audible, but still distinguishable. If you find that the patient is still lacking some high frequency audibility, then the weakest SoundRecover settings that would result in the desired benefit should be applied. Excessive compression should always be avoided. When you believe you have completed the fitting and fine tuning, there are now some behavioral tests including the UWO Plurals Test and the Phonak Phoneme Perception Tests, or PPT, that allow you to assess patient benefit and confirm the fitting parameters.
Readers who would like a complete guide to verification of nonlinear frequency compression with the AudioScan Verifit, can download the guidelines developed by Glista and Scollie (2009) at UWO.
Carolyn: Are there any potential pitfalls or things clinicians should be aware of if they are new to fitting SoundRecover?
Christine: When SoundRecover is applied at very strong settings, below 2 KHz in particular, that could potentially have a detrimental impact on sound quality. At these aggressive settings, not only will consonants be highly compressed, but now we have high frequency information being placed in the spectrum of vowels, and particularly second formant information. This could lead to a detriment in sound quality the patient would not tolerate. SoundRecover is great tool for improving access to sound for patients, but you want to apply it to achieve desired benefit and not more than that. The Phonak Target software will never apply a kneepoint below 1.9 kHz, but it can be manually lowered down to a kneepoint of 1.5 kHz.
A very convenient by-product of SoundRecover is that the risk of feedback can be substantially reduced as a result of changing the output frequency response. However, we do not recommend applying frequency compression specifically as a feedback manager as this could introduce distortion without the benefit of additional audibility. If feedback is an issue, we recommend evaluating the physical fit of the device or earmold, and using the feedback manager as needed.
Carolyn: One thing I was going to mention was that as I was reviewing this article, I cannot believe how much research has been done on this technology and how much is still in progress. There is a lot of evidence behind it.
Christine: There is some amazing guidance available in the literature today. While there are still many questions left to be answered, frequency lowering is one of the most heavily researched hearing instrument features of the last few years, and there has been no waning in interest. I speak to clinicians and researchers on an ongoing basis who are very motivated to continue to answer the clinical questions that exist with SoundRecover, and to expand our understanding of both the benefits and the limitations of this technology. We have good data to work with, along with a steady stream of new data and new insights about this technology.
Carolyn: Thanks again for your time to discuss this exciting technology. Readers who would like more details, information and references about SoundRecover are referred to your recent article, Sound Bytes on SoundRecover.
Glista, D., & Scollie, S. (2009). Pediatric verification considerations for instruments with SoundRecover (non-linear frequency compression) using the latest Audioscan Verifit® tests. National Centre for Audiology, University of Western Ontario, Canada. Retrieved from http://www.phonakpro.com/com/b2b/en/evidence/topics/soundrecover.html
Wolfe, J., John, A., Schafer, E., Nyffeler, M., Boretzki, M., & Caraway, T., et al. (2011). Long-term effects of non-linear frequency compression for children with moderate hearing loss. International Journal of Audiology, 50(6), 396–404. doi: 10.3109/14992027.2010.551788.
Wolfe, J., et al. (2013, submitted). Journal of the American Academy of Audiology.