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Beyond Stethosets: Evaluating the Sound Quality Advantages of Beltone First through Clinical Assessment Stephen A. Hallenbeck, Au.D. Natural, comfortable or otherwise pleasant hearing aid sound quality has been reported by end users as critical Whistle Stop efficiently removes feedback through phase for success with amplification. At the same time, these subjective descriptors highlight the innate ambiguity of cancellation and situation-specific temporary gain reduc- FACTORS INFLUENCING SOUND QUALITY sound quality and the tremendous challenge associated with quantifying these characteristics to ensure the best- tion, often before feedback is even audible to the client. There are several areas which exert an influence over sounding hearing aid is chosen for each client. AFX Music Mode promotes the most accurate feedback sound quality. The first and possibly most important com- cancellation for music without additional sound distortion. ponent of sound quality is related to the primary function of Prospective hearing aid users generally expect that hearing healthcare practitioners will employ their expertise to In sum, the signal processing and advanced directional a hearing aid; specifically, providing the user with audibility efficiently guide them through the decision-making process of which hearing aid will be best suited to them. Fur- and hearing comfort features of Beltone First provide a through prescriptive gain. A common problem encoun- ther, they may not expect to have to try several different hearing aids to determine the best-sounding ones. Given state-of-the-art sound quality experience for users. tered in initial hearing aid fittings is that clients can have 1 adverse immediate reactions to even minimal levels of am- the importance of sound quality and the inherent difficultly with quantifying it, how can professionals effectively and rapidly evaluate hearing aid sound quality to better serve their clients? And do real differences in sound quality across hearing aid manufacturers’ products truly exist? ATTRIBUTES OF BELTONE FIRST QUALITY FOR CLIENTS TM THAT PROMOTE BETTER SOUND QUANTIFYING DIFFERENCES IN HEARING AID SOUND QUALITY ACROSS MANUFACTURERS plification, simply because sounds are perceived differently The hearing aid industry has recognized that the sound the least amount of gain without occluding the ear canal quality of a hearing aid is a major component which influ- would always be judged as the most natural sounding. as compared to their natural, impaired hearing. As such, it could be argued that the hearing aid which provides Beltone hearing aids have always been designed with come the inherent low-cut in amplification from directional ences the acceptance of amplification. Further, manufac- Of course, this strategy is absolutely counterproductive sound quality in mind. Rapid 17 signal processing, which processing while maintaining a purer sound quality. This turers have also recognized that hearing professionals may to rehabilitation through use of amplification, and should models the input signal and applies amplification analo- omnidirectionality in the low frequencies may also permit benefit from more objective methods of evaluating sound be avoided. However, differences in both generic and pro- gous to the ear’s natural processing of sounds, provides an easier listening experience, as clients experience audi- quality, if these objective methods can indeed be derived. prietary prescriptive fitting rules, coupled with the first-fit Beltone with a clear advantage from the start over other tory awareness to all directions for the low frequencies, To address this need, listening panels consisting of individ- strategies designed to provide lower gain at the first-fit, manufacturers who use less-sophisticated compression regardless of the directional pattern. In other words, clients uals with hearing loss were assembled to evaluate sound can influence the sound quality of the instrument being strategies. The selection of three time constants – Syllabic, do not feel as if they are listening “in a tunnel” because off- quality across hearing aid manufacturers. The results of fit. Thus, when evaluating sound quality across manufac- Normal and AVC – enables the professional to personalize axis sounds are inaudible, as occurs with a traditional full these listening panels revealed significant, validated differ- turers, it may be optimal to evaluate sound quality at the the compression characteristics to the client’s needs. Two directional setting. The Mixing Point between this omnidi- ences in sound quality across a variety of manufacturers’ first-fit gain settings as well as at equivalent gain settings types of output compression ensure that very loud sounds rectional and directional processing is adjustable for top- hearing aids (Figure 1). Given that these differences are to ensure a fair and even test. do not exceed the client’s uncomfortable levels, and also level models, allowing the professional greater abilities to present, and that sound quality influences a client’s ac- control the output in each of the processing channels. This fine-tune per the client’s needs. ceptance of amplification, sound quality should definitely Other areas of hearing aid processing which influence be included in the decision-making process of which hear- sound quality include the contributions of hearing aid fea- ing aid is best. tures, such as feedback suppression and directionality. A processing, occurring largely behind-the-scenes, is largely 2 responsible for the sound quality advantages enjoyed by Finally, Beltone’s features designed to maximize hearing Beltone First. comfort round out the sound quality experience. Smart good feedback suppression system will be transparent to Gain Pro enables the listener to move through varied the listener, effectively preventing feedback without add- In addition to superior signal processing, Beltone’s array sound environments throughout the day, with built-in ad- ing any sound distortions or artifacts as byproducts of this of advanced directional features are designed to maintain justments to Sound Cleaner and gain levels. Sound Shifter feedback cancellation. Of course, additional sounds such the integrity of the sound while improving different attrib- enables certain clients to access high-frequency sounds as squeaks and squeals produced by the hearing aid but utes of the signal received by the client. CrossLink Direc- that were previously inaudible to them. Silencer reduces not present in the actual input signal are generally regard- tionality affords every possible binaural directional pattern the gain for low-input sounds in every channel, ensuring ed as detrimental to sound quality by the user. Directional- – bilateral omnidirectional, bilateral directional and asym- that internal processing and external fans and low-level ity can affect sound quality as well, depending on how it is metric directional – in one automatic program, depending motor sounds are not over-amplified. Wind Noise Reduc- implemented by the manufacturer. If low-frequency equali- on the classification of the environment and the location tion reduces amplification of turbulent wind flow around zation of gains is not achieved for directionality, users can of speech sources. However, every directional option pro- the microphones. Synchronized SATISFY gradually and often perceive a difference in loudness when they switch vides split-band processing, with omnidirectionality for low comfortably transitions clients to the optimal levels of gain frequencies and directionality for high frequencies, to over- for best speech intelligibility. And Feedback Eraser with Figure 1. Preference ratings for current hearing aids.2 Error bars indicate 95% confidence intervals. from an omnidirectional to a directional mode, thereby affecting the sound quality. For these reasons, it is usually desirable to clinically assess sound quality with features clinic with a quick change of coupling to the professional’s If the “listen in” option is selected, the following steps can tings. Use coupler or probe microphone measures to enabled, as they would be during the client’s everyday use ears. Alternately, a “listen in” feature available in some help a hearing professional systematically compare sound match the prescribed target outputs, using the same of the hearing aids. verification equipment through the test box or through quality across different hearing aid manufacturers, both at modulated speech signal. Fine tune gains as neces- probe microphone measurements can help the profes- proprietary first-fit and equalized gain settings. sary to achieve matched outputs across the frequency HOW TO ASSESS SOUND QUALITY IN THE CLINIC sional evaluate sound quality in a wider range of controlled sound environments than can be achieved in a typical clin- 1. Program each hearing aid with its proprietary first-fit Due to expectations of end users that hearing profession- ic. The “listen in” feature may also be useful when evaluat- gain settings for a typical sloping hearing loss, with de- als recommend the best-sounding hearing aids for them, ing sound quality for high gain levels, as in some cases the fault feature settings. it is advantageous to evaluate sound quality of different equipment may allow for the “listen in” volume level to be hearing aids at different settings before dispensing them decreased for the professional’s comfort. range. 7. At each of these levels, “listen in” to the hearing aid response. How is the sound quality at each level? Bright or dull? Tinny? Distorted in any way? 2. Through coupler or probe microphone measures, run to clients. The manner in which sound quality is assessed output or Speech Mapping curves with a modulated 8. Select a music input or a “live microphone” on the veri- can vary. A stethoset can be used by the professional to However, each of these three listening test options has its speech signal at soft (55-60 dB SPL), moderate (65-70 fication equipment, and “listen in” on the sound qual- listen to the hearing aid response in the clinic. Along these inherent benefits and drawbacks. Table 1 lists these con- dB SPL) and loud (75-80 dB SPL) levels. Through fine ity produced. Is the sound tinny or distorted? How same lines, behind-the-ear (BTE) or receiver-in-the-ear siderations along with the author’s subjective ranking of tuning of gains, match the prescribed target outputs are loud and soft dynamics reproduced in the hearing (RIE) hearing aids can be worn by the professional in the the quality of these listening test options. (according to manually-entered targets on the verifica- aids? Are any additional squeals produced by the hear- tion equipment, or through visual approximation (“eye- ing aid in response to musical tones? Option Listening Check-Stethoset Wearing the Devices “Listen in” options using the test box and/or probe microphone equipment Table 1. Clinical Sound Quality Testing Options Strengths Weaknesses Overall Quality of Test Quick, easy, simple to complete Unknown input levels; high gain may limit the number of real world cases you can accurately evaluate Good Provides a real-world sound experience with more accurate coupling to the ear than a stethoset provides Difficult to evaluate performance at high gain if the clinician has normal or near normal hearing thresholds; Difficulties coupling to the ear in the case of custom devices Better Controlled environment to systematically and objectively evaluate input signal variations and the hearing aid response Expensive equipment that may not be readily available balling”) of the output targets on the fitting software). 9. (Optional) Systematically turn the various hearing aid 3. At each of these levels, “listen in” to the hearing aid response. How is the sound quality at each level? Bright features on and off to evaluate any impact they have on sound quality. or dull? Tinny? Distorted in any way? Best fication equipment, and “listen in” on the sound qual- FINAL THOUGHTS ON SOUND QUALITY ity produced. Is the sound tinny or distorted? How Sound quality is an elusive, highly individualized, but vital are loud and soft dynamics reproduced in the hearing aspect of hearing aid use. Professionals are challenged to aids? Are any additional squeals produced by the hear- become connoisseurs of hearing aid sound quality, amidst ing aid in response to musical tones? a wide range of hearing aid manufacturers and options. 4. Select a music input or a “live microphone” on the veri- The protocol outlined above is provided as a guideline for 5. Next, choose a prescriptive rule that can be imple- evaluating the sound quality of newly-introduced products mented across all manufacturers. Since many first-fit on the market, as well as for comparisons among current settings employ the manufacturer’s proprietary pre- and older products. Thorough evaluation of sound quality scriptive rule, a generic rule such as NAL-NL2 or DSL can provide a valuable, deeper insight into the technical may be optimal. Program each hearing aid for the possibilities available with hearing aids today. In turn, these same sloping hearing loss with its respective default insights can be used to help counsel clients on realistic ex- feature settings. pectations, and to help troubleshoot user complaints in a more efficient manner. With greater understanding of the 6. Select the chosen generic prescriptive rule in the verifi- quality of sound produced through hearing aid technology, cation equipment and display targets for the same soft, hearing professionals can gain further expertise to provide medium and loud inputs as used with the first-fit set- the best outcomes for their clients. REFERENCES 1. Kochkin S. (2010). Marke trak VIII: Consumer satisfaction with hearing aids is slowly increasing. The Hearing Journal, 63(1), 19-27. 2. Jespersen C. Sound quality in high end hearing instruments. In preparation. M201063-GB-14.02-Rev.A Worldwide Headquarters Beltone A/S Lautrupbjerg 7 DK-2750 Ballerup Denmark Tel.: + 45 45 75 11 11 Fax: + 45 45 75 11 19 www.beltone-hearing.com