Title: Introduction to NALNL1
1Introduction to NAL-NL1
- Harvey Dillon, Gitte Keidser, Denis Byrne,
Richard Katsch, and Teresa Ching - National Acoustic Laboratories and
- Co-operative Research Centre for
- Cochlear Implant and Hearing Aid Innovation
2Proposed fitting procedures for non-linear
hearing aids
- LGOB, IHAFF, DSLi/o, FIG6, and ScalAdapt
- Loudness Normalisation
- Aim To make a sound at any frequency and at any
input level just as loud for the impaired ear as
it is for normal ears
3Why doubt loudness normalisation?
- Dont account for greater loudness of low
frequencies of speech
4International Long-term Average Speech Spectrum
5Loudness perception
6Loudness perception
7Why doubt loudness normalisation?
- Dont account for greater loudness of low
frequencies of speech - Dont account for reduced effectiveness of
audibility at frequencies of greatest hearing
loss
8Effect of hearing loss
1
Normal hearing
Effective audibility
hearing impaired
0
30
0
Sensation level (dB)
9Why doubt loudness normalisation?
- Doesnt account for greater loudness of low
frequencies of speech - Doesnt account for reduced effectiveness of
audibility at frequencies of greatest hearing
loss - Research shows that normalisation is not correct
for average speech inputs
10Rationale of NAL-NL1 procedure
- Maximise speech intelligibility for any input
level - For each input level, make overall loudness of
speech equal to, or less than, normal
11Predicting speech intelligibility
Level distortion factor
1
0
73
30
1/3 octave SPL
Threshold
Frequency
12Predicting speech intelligibility
Level distortion factor
- SII ? Wi.Ii.Li
- SII ? Weffi.Ii.Li
1
0
73
30
1/3 octave SPL
Threshold
Frequency
13Predicting loudness
- Loudness model of Moore and Glasberg
Calculate loudness per band
Sum across bands
Filtering into auditory bands
External middle ear
14Predicting loudness
- Loudness model of Moore and Glasberg
Calculate loudness per band
Sum across bands
Filtering into auditory bands
External middle ear
Allowance for hearing loss
15The derivation
- Choose an audiogram
- Choose an input level
- Calculate normal loudness
- Juggle gains until SII is a maximum
and loudness is
normal or less
16The derivation (cont)
- Repeat for several input levels,
- Repeat for many audiograms,
- Fit an equation to these optimum gains.
17NAL-NL1 insertion gain
- IG at each frequency, depends on
- HTL at that frequency
- 3 freq. Average HTL (500, 1000, 2000 Hz)
- Slope from 500-2000 Hz
- Overall speech input level
- Thus, gain at any frequency depends on HTL at
several frequencies, as for NAL-RP
18Observations on prescriptions
- Loudness is approximately constant across
frequency
80
65
Specific Loudness
50
Frequency
19Observations on prescriptions
- Loudness is approximately constant across
frequency - Gain-frequency response does not normalise
loudness across frequency
80
65
Specific Loudness
50
Frequency
Loudness
500
3k
20Observations (cont)
- At medium levels, gain and frequency response
agree with NAL-RP
21Access to NAL-NL1
- NAL-NL1 Stand-alone Clinician software
(www.nal.gov.au) - Hearing aid manufacturers software and analysing
equipment (Bernafon, Frye Electronics,
Intrason, Rion, Siemens, Sonic Innovations,
Starkey, Unitron, Viennatone)
22Evaluation of NAL-NL1
23Fitting Wide Dynamic Range Compression Hearing
Aids
- Gitte Keidser, Harvey Dillon,
- and Frances Grant
- National Acoustic Laboratories and
- Co-operative Research Centre for
- Cochlear Implant and Hearing Aid Innovation
24Fitting WDRC Devices
- Fitting rationale
- Number of channels
- OSPL90 prescription
- Conductive component
- Verifying the response
- Multiple memories
25Fitting Rationale
- Loudness Normalisation or Speech Intelligibility
Maximisation?
26Test design
- Prescription procedures IHAFF and NAL-NL1 (two
channels) - Twenty-four subjects flat and steeply sloping
losses - Laboratory tests paired comparison and speech
recognition (BKB sentences) - Field test (4-6 weeks) satisfaction rating and
description of performance in individually
selected listening situations
27(No Transcript)
28Prescribed CR
LF
HF
29Paired Comparison
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31(No Transcript)
32Speech recognition test
33Field test
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35Recommendation
- Use NAL-NL1 as starting point
- If NAL-NL1 is very different from LN then NAL-NL1
is preferred - If difference from LN is small then the preferred
response shape is reached during fine-tuning
36How many Channels?
37Multi-channel compression
Advantages
- Improved audibility (especially for sloping
losses) - Improved SNR when noise is dominant in a
restricted range of frequencies
38Multi-channel compression
- Past research based on loudness normalisation
procedures - LN procedures prescribe high CRs and low CTs
- High CR and low CT negatively affect speech
intelligibility in multi-channel schemes
39Test design
- NAL-NL1 implemented in one, two and four channels
- Twenty-four subjects flat and steeply sloping
losses - Laboratory tests paired comparison and speech
recognition (BKB sentences) - Field test (4-6 weeks) satisfaction rating and
description of performance in individually
selected listening situations
40Paired comparison
41Input/Output curves (all)
f 300 Hz
f 800 Hz
f 2000 Hz
f 4000 Hz
42Speech recognition test(in traffic noise)
43Field test
44Discriminating factors
45Recommendation
- For clients with sloping losses use at least two
compression channels - For clients with flat losses the number of
compression channels is probably unimportant
46Questions
47OSPL90 Prescription
- Not to high - not too low
48OSPL90 in WDRC devices
- OSPL90 is less critical because gain decreases
when input level increases
21 comp.
Linear
49OSPL90 in WDRC devices
- Use the same OSPL90 prescription as for linear
devices - Most based on avoiding discomfort, so set just
below LDL - POGO 4 dB below 3FA LDL
- Cox (1985) 100 dB SPL 1/2 HTL
- NAL-SSPL halfway between minimum and maximum
output limit
50OSPL90 in WDRC devices
- In most cases the OSPL90 level produced is below
what is prescribed - Is OSPL90 too low? - likely to depend on the
prescribed compression characteristic
51Multi Channel Hearing Aids
- Limiting may occur on the wideband signal after
the channels are recombined, or independently in
each channel before the channels are recombined - If OSPL90 can be independently adjusted in each
channel - allow for effects of power and loudness
summation
52Multi Channel Hearing Aids
Total Leq 110 dB SPL
Total Leq 115 dB SPL
53Conductive Component
54Prescribed Gain
- Linear devices apply additional gain equal to
75 of the conductive component - It is possible that for non-linear devices, 100
of the conductive component can be applied to
low-level signals ( increased CR)
55Prescribed OSPL90
- If OSPL90 is prescribed on the basis of measured
UCL use procedure as is - If using NAL-SSPL 1) Prescribe OSPL90 for
sensorineural part, 2) increase OSPL90 by 87.5
of conductive component (Min. Limit increases by
75 and Max. Limit increases by 100 )
56Verifying the Fitting
57Real-ear measurements?
YES
- Real-ear gain at different input levels (e.g. 50,
65, and 80 dB SPL)
- Real-ear gain at one input level (e.g. 65 dB SPL)
and input/output curves (one for each compression
channel)
Use a broadband stimulus for measuring gain
58Subjective evaluation
- Check that speech presented at 50, 65, and 80 dB
SPL are rated about soft, comfortable, and
loud - If speech at 80 dB SPL is rated loud the OSPL90
is not too low - If other high-level sounds are acceptable the
OSPL90 is not too high
59Multiple memories
- Candidacy and selecting alternative amplification
characteristics
60Candidacy
Criteria
- Difficulty hearing in acoustically diverse
conditions - Can understand and manage multi-memory concept
- Variation in low frequency real-ear gain of at
least 5 dB achievable - Average high frequency hearing loss greater than
55 dB HL
61Client needs help hearing in acoustically diverse
listening situations? (interview or COSI)
62Response variation
- Prescriptive responses
- known to be effective
- based on audiogram
- Use NAL-RP as reference to compensate for the
individual hearing loss
63Response selection
LISTENING CONDITION
PREFERRED RESPONSE
- Speech in quietSpeech in reverberation
NAL responseSpeech in babble-noise__________
______________________________________________ - Ease of understanding a dialogue High
frequency comp.(distant talkers, soft voice)
(CR 41, CT 55 dB)___________________
_____________________________________ - Ease of understanding speech in Steeper
responselow frequency background noise
(re. NAL response, 4-6 dB)_______________________
_________________________________ - Reduce annoyance of low Low
frequency comp.frequency background noise
(CR 21, CT 55 dB)
__________________________________________________
______ - Reduce annoyance of high Flatter
responsefrequency background noise
(re. NAL response, 4-6 dB)
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65Linear variation
NAL-RP as base response
NAL-RP
LF
NAL-RP
HF
66Linear variation
NAL-RP as base response
NAL-RP
LF
Flatter
NAL-RP
HF
Flatter
67Linear variation
NAL-RP as base response
NAL-RP
LF
Flatter
Steeper
NAL-RP
HF
Steeper
Flatter
68Linear variation
NAL-RP as base response
NAL-NL1 as base response
NAL-RP
NAL-NL1
LF
LF
Flatter
Steeper
NAL-RP
NAL-NL1
HF
HF
Steeper
Flatter
69Linear variation
NAL-RP as base response
NAL-NL1 as base response
NAL-RP
NAL-NL1
LF
LF
Flatter
Steeper
NAL-RP
NAL-NL1
HF
HF
Steeper
Flatter
70Linear variation
NAL-RP as base response
NAL-NL1 as base response
NAL-RP
NAL-NL1
LF
LF
Flatter
Steeper
NAL-RP
NAL-NL1
HF
HF
Steeper
Flatter
71Linear variation
NAL-RP as base response
NAL-NL1 as base response
NAL-RP
NAL-NL1
LF
LF
Flatter
Steeper
Increase or decrease gain, and keep CR and CT
the same
NAL-RP
NAL-NL1
HF
HF
Steeper
Flatter
72Non-linear variation
NAL-RP as base response
NAL-RP
LF
NAL-RP
HF
73Non-linear variation
NAL-RP as base response
NAL-RP
LF
LF comp.
NAL-RP
HF
74Non-linear variation
NAL-RP as base response
NAL-NL1 as base response
NAL-RP
NAL-NL1
LF
LF
LF comp.
NAL-RP
NAL-NL1
HF
HF
75Non-linear variation
NAL-RP as base response
NAL-NL1 as base response
NAL-RP
NAL-NL1
LF
LF
LF comp.
NAL-RP
NAL-NL1
HF
HF
76Non-linear variation
NAL-RP as base response
NAL-NL1 as base response
NAL-RP
NAL-NL1
LF
LF
LF comp.
Increase CR and decrease CT in low frequency
band
NAL-RP
NAL-NL1
HF
HF
77Non-linear variation
NAL-RP as base response
NAL-RP
LF
NAL-RP
HF
78Non-linear variation
NAL-RP as base response
NAL-RP
LF
LF comp.
NAL-RP
HF
HF comp.
79Non-linear variation
NAL-RP as base response
NAL-NL1 as base response
NAL-RP
NAL-NL1
LF
LF
LF comp.
NAL-RP
NAL-NL1
HF
HF
HF comp.
80Non-linear variation
NAL-RP as base response
NAL-NL1 as base response
NAL-RP
NAL-NL1
LF
LF
LF comp.
NAL-RP
NAL-NL1
HF
HF
HF comp.
81Non-linear variation
NAL-RP as base response
NAL-NL1 as base response
NAL-RP
NAL-NL1
LF
LF
LF comp.
Increase CR in both bands. Decrease CT in LF
band and increase CT in HF band
NAL-RP
NAL-NL1
HF
HF
HF comp.
82Notice
- Verify fitting using insertion gain
- Ensure that client can tell the programs apart
- Follow-up 3-4 weeks later - adjust or try
alternative, if needed - We dont know the best combination of response
variation and hearing aid facility
83The end
84NAL-SSPL (Dillon Storey)
- Defined min. limit to avoid saturation (re. 75 dB
SPL speech amplified according to NAL-RP) - Defined max. limit to avoid discomfort (re.
measured LDL values) - Prescription midway between the two limits
- Evaluation Suitable for 80 of subjects, but
always verify the OSPL90 setting!
85NAL-SSPL Procedure
86Multi Channel Hearing Aids
Number of channels Reduction (dB) 1
0 2 5 3 7 4 9 5 10
87Otosclerosis
- A possible change in bone conduction thresholds
because of stiffening or fixation of the stapes - Decrease bone conduction thresholds before
calculating gain for either the s/n or the
conductive component
88Prescribed Gain
- For conductive HLoss HTL, MCL and LDL are all
increased by the same amount, however, do not
prescribe 1 dB of gain for every 1 dB of HLoss - Not researched, but apply additional gain equal
to 75 of the conductive component - It is possible that for non-linear devices, 100
of the conductive component can be applied to
low-level signals ( increased CR)