Desired Sensation Level

(DSL-V5)

National Acoustic Lab NL 2

(NAL-NL2)

Goal of Fitting Formula

DSL [i/o]/v5

Goal is to provide the wearer with an audible and

comfortable signal in each frequency region

Does not attempt to make sounds equally loud in each

frequency region

Goal of Fitting Formula

NAL/NL2

Goal is to maximize speech intelligibility at the listening

level preferred by the wearer

Intelligibility is assumed to be maximized when all

bands of speech are perceived to have the same

loudness (loudness equalization)

Desired Sensation Level

The DSL Method makes use of HL audiometric data

and converts it to SPL at the eardrum (using the Real-

Ear-To-Coupler-Difference (RECD) measurement)

Like other prescriptive measures, the goal is to select

hearing aid frequency and gain characteristics that place

as much as possible of the long-term speech spectrum

(LTASS) into the amplified range

DSL version 5.0

New version prescribes a higher level of gain and output

in the pediatric/congenital prescription than in the

adult/acquired prescription

Motivation Behind Development

First, children with hearing loss are being identified at

birth and amplification is being provided to infants by 6

months of age

(Joint Committee on Infant Hearing, 2000; American Academy of

Audiology, 2003)

Secondly, improvements in auditory brainstem response

(ABR) testing procedures, and significant advances in

hearing instrument technology make continued

development both desirable and necessary

Finally, clinicians still desire access to generic

prescriptive algorithms relative to manufacturer-specific

proprietary fitting algorithms, especially for their

pediatric clients

Given all these considerations, work was initiated in the

late 1990s on a new version of the DSL Method (DSL

v5.0) which includes the DSL multi-stage input/output

algorithm, referred to as DSL m[i/o]

DSL v5

•Audible and comfortable speech cues in all listening

situations is the main goal.

• Less overall gain than in the previous DSL

• Offers output limiting that is more appropriate for the

speech signal.

• Channel-matching to the specific instrument

DSL v5

• Supports severe-to-profound hearing losses

• Corrections for mixed and conductive hearing losses

• Supports binaural fittings

Has four different prescriptions

•Kids in quiet

•Kids in noise

•Adults in quiet

•Adults in noise

DSL v5 Child

DSL v5 Child targets are formulated for congenital

hearing loss, regardless of age

An adult that has a congenital hearing loss has likely

been provided with amplified levels of sound that are

more consistent with what the DSL v5 Child target

criteria provide

DSL v5 Child

The goal was to keep the DSL v5 Child targets as close

to the DSL [i/o] targets as possible

However, for more severe hearing losses, the targets for

average conversational speech are lower. This is due to

a correction that aims to ensure that the peaks of speech

are within the patient's auditory area and not saturating

the hearing aid

DSL v5 Adult

DSL v5 Adult targets are formulated for those who have

acquired hearing loss. The Adult targets are

approximately 7 dB lower than the targets for children

DSL v5 Adult

The difference between the adult and child prescription

decreases for people with a severe-to-profound hearing

loss, which is a desired effect because it maintains

audibility of speech

NAL-NAL2

NAL-NL2, like NAL-NL1, is a threshold-based

procedure that prescribes gain-frequency responses for

different input levels, or the compression ratios at

different frequencies, in wide dynamic range

compression hearing aids

NAL-NAL2

The goal of NAL- NL2 remains to maximize speech

intelligibility for any input level of speech above the

compression threshold, while keeping the overall

loudness of speech at or below normal overall loudness

NAL-NL2 stages

Motivation behind NAL-NL2

NAL-NL1 was often perceived as too loud

NAL-NAL2

• Changed the intelligibility modeling so that new target

gain provides more speech intelligibility

More gain for soft sounds (more compression) less

gain for low frequencies

NAL-NAL2

Considers additional individual factors:

• Age: More gain for children than adults

• Experience: More gain for more experienced users

• Gender: More gain for male users

• Language: More low frequency gain & less high

• frequency gain for tonal languages

• Dead regions of the cochlea

• Cognitive ability

• Frequency selectivity

Comparison between DSL V.5.0 and

NAL-NLNAL- NLDSL version 5.0

Thresholds obtained via

headphones, insert

phones,

Thresholds obtained via

headphones, insert

phones, sound field and

electrophysiologic

measures

Audiometric data that

can be used to derive

targets

Yes Yes Adjustment for

conductive/mixed loss

Yes Yes Adjustment for binaural

fitting

Yes, RECDYes, RECD, REDD and

REUR

Individual specific data

can be entered and used

in deriving targets

NAL- NLDSL version 5.0

Yes NoDesensitization factor

Choose between 1 and 4

channels

YesAccounts for number of

channels

Prescription designed to

amplify speech such

that at a given level

intelligibility is

maximized with the

constraints of

normalizing overall

loudness. Resulting

targets similar to those

of LE approach

Loudness normalization,

placement of acoustic

cues available to normal

hearing listener into

dynamic range of

listener with hearing

loss (given certain

constraints)

Underlying rationale/

goal

Yes but recommends

midlevel CT

Yes but recommends

choice of CT based on

degree of loss

Allows for choice of CT

Yes Yes Adjustment for

venting/tubing

Audiology: Treatment

By Michael Valente, Holly Hosford-Dunn, Ross J. Roeser

NAL- NLDSL version 5.0

Yes Yes Adjustment for

venting/tubing

Yes Yes Age related adjustments

for ear canal

characteristics

No Yes Age related adjustments

for audibility

No Yes Adjustment for hearing

aid experience

Coupler targets, real ear

gain targets, REIG,

aided threshold targets,

SPL-O-GRAMS and

hearing aid parameters

(CT, CF, C…. etc.,)

Coupler targets, real ear

aided targets, real ear

gain targets, aided

threshold targets, SPL-

O-GRAMS and hearing

aid parameters (CT, CF,

C…. etc.,)

Fitting information

provided