The Desired Sensation Level multistage input/output algorithm

Abstract

The Desired Sensation Level (DSL) Method was revised to support hearing instrument fitting for infants, young children, and adults who use modern hearing instrument technologies, including multichannel compression, expansion, and multimemory capability. The aims of this revision are to maintain aspects of the previous versions of the DSL Method that have been supported by research, while extending the method to account for adult-child differences in preference and listening requirements. The goals of this version (5.0) include avoiding loudness discomfort, selecting a frequency response that meets audibility requirements, choosing compression characteristics that appropriately match technology to the user's needs, and accommodating the overall prescription to meet individual needs for use in various listening environments. This review summarizes the status of research on the use of the DSL Method with pediatric and adult populations and presents a series of revisions that have been made during the generation of DSL v5.0. This article concludes with case examples that illustrate key differences between the DSL v4.1 and DSL v5.0 prescriptions.

Figure 1.

Stimulus levels used for loudness ratings of passages of speech. Calibration targets for three overall levels of speech are shown: soft speech (53 dB SPL, ∘), average speech (70 dB SPL, +), and loud speech (83 dB SPL, ♦), all referred to the free field (FF). The measured 1/3-octave band spectra at each overall level are shown by the solid lines.

Figure 2.

Observed limits of fit to targets for 89 ears in a clinical study using DSL with adult hearing instrument users. The highest and lowest audiometric frequencies that were within 5 dB of target are shown against the average hearing level of the fitted ear. Target reference was the DSL 4.1 target for speech-level inputs at 70 dB SPL. PTA = pure-tone average.

Figure 3.

Aided loudness ratings for both normally hearing listeners and hearing instrument users. The mean and the ± 2 standard deviation range for the normally hearing listeners are plotted as solid lines. The mean aided loudness ratings (•) from the hearing instrument users are shown, along with the ± 2 standard deviation range (vertical bars). Most hearing instrument users had aided loudness ratings that were within the normal range. See Table 1 for category descriptors. FF = free field.

Figure 4.

Unaided (Panel A) vs Aided (Panel B) results obtained from the speech-in-noise (SIN) test of hearing impaired listeners. Mean performance is shown (▪) along with the 95% confidence interval (vertical bars). The performance of a sample of normally hearing listeners is also shown (95% confidence interval, solid lines).

Figure 5.

Listening and communication situations nominated by adult hearing instrument users as priorities for hearing instrument fitting on the Client Oriented Scale of Improvement.

Figure 6.

Results of the Client Oriented Scale of Improvement for a sample of adult hearing instrument users fitted using the DSL Method. Panel A shows Degree of Change scores. Panel B shows Final Ability scores. Each bar indicates the number of respondents indicating a given outcome rating. Results are shown for the self-nominated communication situations, in order of situation priority, as well as the average rating across situations for each listener.

Figure 7.

Recommended vs preferred listening levels (measured in 2-cc coupler gain at 2000 Hz) for three groups of subjects: children (□), new adult hearing instrument users (Δ), and experienced adult hearing instrument users (•). Regression lines (see text for details) are shown for each subject group, along with a diagonal line at target listening levels.

Figure 8.

Comparison of DSL v4.1 targets derived using ANSI 1989 and ANSI 1996 audiometric calibration standards. Filled symbols represent targets generated using ANSI 1989 values and open symbols show targets from ANSI 1996. The solid and dashed lines without symbols represent minimum audible pressure (MAP) values used in DSL v4.1 and ANSI 1996 occluded ear simulator (OES).

Figure 9.

Unaided long term average speech spectra assumed by the DSL Method in versions 4.1 (thin lines) and 5.0 (thick lines) when representing low-, moderate-, and high-level speech. See text for specific details regarding sources and overall levels.

Figure 10.

The DSL[i/o] target input/output function (thick line) for a 50 dB HL threshold at 1000 Hz, computed using a loudness normalization strategy. The input levels are plotted in dB SPL in the sound field (SF). The output levels are plotted in dB SPL in the real ear (RE). The dashed lines represent the limits of the auditory area at this frequency. The diagonal line represents unaided signals (unity gain). Detection thresholds have been converted to dB RE SPL and used to predict upper limits of comfort (both shown by dashed lines).

Figure 11.

Conceptual illustration of the computational stages included in the DSLm[i/o] algorithm. WDRC = wide-dynamic-range compression.

Figure 12.

Electroacoustic evaluation of two high-level signals measured on the same hearing instrument. Displayed curves indicate the measured levels of an aided 90 dB SPL pure-tone sweep (*), the aided dynamic range (thin lines) and long-term average speech spectrum (thick line) of speech are presented at 82 dB SPL. Insets show input/output plots for the same aid, measured for speech-weighted noise (right) and pure tones (left) at 500 (*), 1000 (□), 2000 (⋄), and 4000 Hz (+).

Figure 13.

Target real-ear aided response (REAR) levels for four frequencies from two prescriptive formulas (DSL[i/o] and NAL-NL1) for flat hearing threshold levels ranging from 0 through 110 dB HL. Target calculations assume an adult user, TDH phones, and a behind-the-ear-style hearing instrument with one channel.

Figure 14.

Comparison of measured crest factor for speech from linear hearing instruments vs either nonlinear, fast-acting hearing instruments (a) or nonlinear, multichannel hearing instruments (b).

Figure 15.

Comparison of DSL[i/o] and DSLm[i/o] target input/output functions, shown as thick and thin lines respectively. The dashed lines mark the detection thresholds and upper limits of comfort. The target level for 60-dB speech in this band is also shown for reference (•). See Figure 10 for fitting details. RE = real ear; BOLT = broadband output limiting threshold; WDRC = wide-dynamic-range compression.

Figure 16.

Relation between hearing threshold levels (dB HL) and proposed input levels (dB SPL in the sound field) for the wide-dynamic-range compression (WDRC) threshold. The solid line is a third-order polynomial fit to a set of hypothesized compression threshold values (•). Dashed lines indicate the range of speech inputs considered by DSL 5 (i.e., 52 and 74 dB SPL), for reference.

Figure 17.

Comparison of monaural and binaural target input/output functions generated by the DSLm[i/o] algorithms, shown as thin and thick lines respectively. See Figure 10 for fitting details.

Figure 18.

Comparison of pediatric/congenital and adult/acquired target input/output functions generated by the DSLm[i/o] algorithms, shown as thin and thick lines respectively. See Figure 10 for fitting details.

Figure 19.

Average real-ear output targets for DSL v5.0 as a function of four-frequency pure-tone average threshold values (dB HL), for pediatric/congenital and adult/acquired target types in DSL v5.0. PTA = pure-tone average; RESP = real-ear sound pressure level.

Figure 20.

Effect of applying a conductive correction to the prescribed gains for conversational speech. Prescribed 2-cc coupler gains (average gain for 500, 1000, 2000 Hz) for four flat hearing losses are shown, assuming either sensorineural loss or various degrees of conductive overlay within the stated hearing threshold level.

Figure 21.

(a) DSL v5.0 prescriptive targets for a pediatric hearing instrument user for a speech input of 70 dB SPL (solid heavy line), displayed in an SPLogram format that shows threshold (○), predicted upper limit of comfort (*), and the DSL v4.1 targets for 70 dB SPL speech (+). All targets are shown as long-term average speech spectra in 1/3-octave bands. (b) DSLlm[i/o] targets for speech at 60 dB SPL input levels are shown by the thin line.

Figure 22.

DSL v5.0 and DSL v4.1 (+) prescriptive targets for pediatric hearing instrument user with a sloping hearing loss. Format follows that of Figure 21. Panel a: Targets for the Long Term Average Speech Spectrum are shown. Panel b: Assumed levels of the peaks and valleys of speech are superimposed (- - -).

Figure 23.

DSL v5.0 and DSL v4.1 (+) prescriptive targets for a pediatric hearing instrument user and an adult hearing instrument user with equivalent hearing losses of 50 dB HL and equivalent ear canal acoustics. Format follows that of Figure 21. Panel a shows targets for the pediatric user, for speech inputs of 52, 60, 70, and 74 dB SPL. Panel b shows targets for the adult user for the same input levels.