NAL-NL2 Empirical Adjustments

NAL-NL1, the first procedure from the National Acoustic Laboratories (NAL) for prescribing nonlinear gain, was a purely theoretically derived formula aimed at maximizing speech intelligibility for any input level of speech while keeping the overall loudness of speech at or below normal loudness. The formula was obtained through an optimization process in which speech intelligibility and loudness were predicted from selected models. Using updated models and applying some revisions to the derivation process, a theoretically derived NAL-NL2 formula was obtained in a similar way. Further adjustments, directed by empirical data collected in studies using NAL-NL1 as the baseline response, have been made to the theoretically derived formula. Specifically, empirical data have demonstrated that (a) female hearing aid users prefer lower overall gain than male users; (b) new hearing aid users with more than a mild hearing loss prefer increasingly less gain with increasing degree of hearing loss than experienced hearing aid users, and require up to 2 years to adapt to gain levels selected by experienced hearing aid users; (c) unilaterally and bilaterally fitted hearing aid users prefer overall gain levels that vary less than estimated by the bilateral correction factor; (d) adults prefer lower overall gain than children; and (e) people with severe/profound hearing loss prefer lower compression ratios than predicted when fitted with fast-acting compression. The literature and data leading to these conclusions are summarized and discussed in this article, and the procedure for implementing the adjustments to the theoretically derived NAL-NL2 formula is described.

[1]  Benjamin W Y Hornsby,et al.  Using trainable hearing aids to examine real-world preferred gain. , 2008, Journal of the American Academy of Audiology.

[2]  R. Plomp Noise, Amplification, and Compression: Considerations of Three Main Issues in Hearing Aid Design , 1994, Ear and hearing.

[3]  Hugh J. McDermott,et al.  The Design and Evaluation of a Hearing Aid with Trainable Amplification Parameters , 2007, Ear and hearing.

[4]  G Keidser,et al.  Comparing Loudness Normalization (IHAFF) with Speech Intelligibility Maximization (NAL-NL1) when Implemented in a Two-Channel Device , 2001, Ear and hearing.

[5]  Justin A. Zakis,et al.  Preferred overall loudness. II: Listening through hearing aids in field and laboratory tests , 2006, International journal of audiology.

[6]  R M Cox,et al.  Maturation of hearing aid benefit: objective and subjective measurements. , 1992, Ear and hearing.

[7]  M. Florentine,et al.  Measures of the ecological loudness of speech , 2011 .

[8]  Harvey Dillon,et al.  A cross-over, double-blind comparison of the NAL-NL1 and the DSL v4.1 prescriptions for children with mild to moderately severe hearing loss , 2010, International journal of audiology.

[9]  Gitte Keidser,et al.  Clinical Evaluation of Australian Hearing's Guidelines for Fitting Multiple Memory Hearing Aids , 2005 .

[10]  I Hochberg,et al.  Most comfortable listening for the loudness and intelligibility of speech. , 1975, Audiology : official organ of the International Society of Audiology.

[11]  R Plomp,et al.  The negative effect of amplitude compression in multichannel hearing aids in the light of the modulation-transfer function. , 1988, The Journal of the Acoustical Society of America.

[12]  R A Bentler,et al.  An Examination of Several Characteristics that Affect the Prediction of OSPL90 in Hearing Aids , 2001, Ear and hearing.

[13]  Harvey Dillon,et al.  Evaluation of the NAL-NL1 and DSL v4.1 prescriptions for children: Preference in real world use , 2010, International journal of audiology.

[14]  APPLICATION OF A "RELATIVE" PROCEDURE TO A PROBLEM IN BINAURAL BEAT PERCEPTION. REP 63-17. , 1963, [Report]. Civil Aeromedical Research Institute.

[15]  Larry E Humes,et al.  Changes in hearing-aid benefit following 1 or 2 years of hearing-aid use by older adults. , 2002, Journal of speech, language, and hearing research : JSLHR.

[16]  C V Palmer,et al.  The functionally and physiologically plastic adult auditory system. , 1998, The Journal of the Acoustical Society of America.

[17]  I. M. Ventry,et al.  Most comfortable loudness for pure tones, noise, and speech. , 1971, The Journal of the Acoustical Society of America.

[18]  Harvey Dillon,et al.  NAL-NL1: A new procedure for fitting non-linear hearing aids , 1999 .

[19]  P. Newall,et al.  Hearing aid gain and frequency response requirements for the severely/profoundly hearing impaired. , 1990, Ear and hearing.

[20]  D Byrne,et al.  Evaluation of the National Acoustic Laboratories' new hearing aid selection procedure. , 1988, Journal of speech and hearing research.

[21]  B E Walden,et al.  Binaural loudness summation in the hearing impaired. , 1987, Journal of speech and hearing research.

[22]  Gitte Keidser,et al.  Variation in preferred gain with experience for hearing-aid users , 2008, International journal of audiology.

[23]  T. Ching,et al.  Children's speech perception and loudness ratings when fitted with hearing aids using the DSL v.4.1 and the NAL-NL1 prescriptions , 2010, International journal of audiology.

[24]  R C Seewald,et al.  The input/output formula: a theoretical approach to the fitting of personal amplification devices. , 1995, The Journal of the Acoustical Society of America.

[25]  Gitte Keidser,et al.  A Review and Analysis: Does Amplification Experience Have an Effect on Preferred Gain over Time? , 2005 .

[26]  Gitte Keidser,et al.  The preferred response slopes and two-channel compression ratios in twenty listening conditions by hearing-impaired and normal-hearing listeners and their relationship to the acoustic input , 2005, International journal of audiology.

[27]  G Keidser,et al.  NAL-NL1 procedure for fitting nonlinear hearing aids: characteristics and comparisons with other procedures. , 2001, Journal of the American Academy of Audiology.

[28]  Gitte Keidser,et al.  Client-Based Adjustments of Hearing Aid Gain: The Effect of Different Control Configurations , 2008, Ear and hearing.

[29]  Jeremy Marozeau,et al.  Testing the binaural equal-loudness-ratio hypothesis with hearing-impaired listeners. , 2009, The Journal of the Acoustical Society of America.

[30]  Jeremy Marozeau,et al.  Monaural and binaural loudness of 5- and 200-ms tones in normal and impaired hearing. , 2006, The Journal of the Acoustical Society of America.

[31]  Gitte Keidser,et al.  The effect of the base line response on self-adjustments of hearing aid gain. , 2008, The Journal of the Acoustical Society of America.

[32]  H. Dillon,et al.  The National Acoustic Laboratories' (NAL) New Procedure for Selecting the Gain and Frequency Response of a Hearing Aid , 1986, Ear and hearing.

[33]  Mary Florentine,et al.  Binaural Loudness Summation for Speech and Tones Presented via Earphones and Loudspeakers , 2009, Ear and hearing.

[34]  Earl E. Johnson,et al.  A comparison of gain for adults from generic hearing aid prescriptive methods: impacts on predicted loudness, frequency bandwidth, and speech intelligibility. , 2011, Journal of the American Academy of Audiology.

[36]  H Levitt,et al.  The effect of compression ratio and release time on the categorical rating of sound quality. , 1998, The Journal of the Acoustical Society of America.

[37]  Gitte Keidser,et al.  The trainable hearing aid: What will it do for clients and clinicians? , 2006 .

[38]  Sheila Moodie,et al.  The Desired Sensation Level Multistage Input/Output Algorithm , 2005, Trends in amplification.

[39]  Gitte Keidser,et al.  Derivation of the NAL-NL2 prescription procedure , 2010 .

[40]  Anna K Nabelek,et al.  The influence of listener's gender on the acceptance of background noise. , 2003, Journal of the American Academy of Audiology.

[41]  J. Hall,et al.  Diotic loudness summation in normal and impaired hearing. , 1985, Journal of speech and hearing research.

[42]  Braida Ld,et al.  Multiband compression limiting for hearing-impaired listeners. , 1987 .

[43]  Directional audiometry. 3. The influence of azimuth on the perception of speech in patients with monaural hearing loss. , 1971, Acta oto-laryngologica.

[44]  J. Landes Application of a J-Q Model for Fracture in the Ductile-Brittle Transition , 1997 .

[45]  L D Braida,et al.  Multiband compression limiting for hearing-impaired listeners. , 1987, Journal of rehabilitation research and development.

[46]  Brian C J Moore How Much Do We Gain by Gain Control in Hearing Aids? , 1990 .

[47]  Gitte Keidser,et al.  Preferred low- and high-frequency compression ratios among hearing aid users with moderately severe to profound hearing loss. , 2007, Journal of the American Academy of Audiology.

[48]  Harvey Dillon What ’ s New in Prescriptive Fittings Down Under ? Gitte Keidser , .

[49]  Gitte Keidser,et al.  Effect of low-frequency gain and venting effects on the benefit derived from directionality and noise reduction in hearing aids , 2007, International journal of audiology.

[50]  Brian C J Moore,et al.  Development of a new method for deriving initial fittings for hearing aids with multi-channel compression: CAMEQ2-HF , 2010, International journal of audiology.

[51]  R M Cox,et al.  The Contour Test of Loudness Perception , 1997, Ear and hearing.

[52]  C W Turner,et al.  The Time Course of Hearing Aid Benefit , 1997, Ear and hearing.

[53]  Wouter A. Dreschler,et al.  The Effects of Syllabic Compression and Frequency Shaping on Speech Intelligibility in Hearing , 1994, Ear and hearing.

[54]  Robyn M. Cox,et al.  Using Loudness Data for Hearing Aid Selection: The IHAFF Approach , 1995 .

[55]  P. Dermody,et al.  Loudness Summation with Binaural Hearing Aids , 1975 .

[56]  Wouter A Dreschler,et al.  Audiologist-Driven Versus Patient-Driven Fine Tuning of Hearing Instruments , 2012, Trends in amplification.