Figures for Chapter 9
Prescription
Dillon (2001)
Hearing Aids
140
120
Dynamic range and
hearing loss
UCL
dB HL
100
80
MCL
60
Threshold
40
0
20
40
60
80
100 120
Hearing threshold (dB HL)
Figure 9.1 Uncomfortable listening level and most comfortable level for
people with sensorineural hearing loss, averaged across 500, 1k, 2k, and 4
kHz. Data shown with filled symbols are from Schwartz et al. (1988) and those
with open symbols are from Pascoe (1988). The dashed line has a slope of
0.5, illustrating the relationship between MCL and the half-gain rule.
Source: Dillon (2001): Hearing Aids
Insertion gain (dB)
NAL-R for a flat loss
30
20
10
0
125 250
500 1k 2k
4k
Frequency (Hz)
8k
Figure 9.2 The insertion gain response prescribed by the NAL-R formula for a
flat 40 dB hearing loss.
Source: Dillon (2001): Hearing Aids
Desired Sensation Level
(dB)
Desired sensation levels
60
50
40
30
20
10
0
0
20
40
60
80
100 120
Hearing Threshold (dB HL)
Figure 9.3 Sensation level targets for the Desired Sensation Level
method as a function of hearing threshold, at 1 kHz. Values are very
similar at other frequencies.
Source: Dillon (2001): Hearing Aids
Hearing threshold (dB HL)
Frequency (Hz)
125 250 500 1k 2k 4k
8k
0
20
40
Figure 9.4 Audiogram of a
mild, gently sloping
sensorineural hearing loss,
and insertion gains prescribed
by the DSL (triangles), POGOII (squares) and NAL-RP
(diamonds) procedures.
60
80
100
Insertion gain (dB)
120
35
30
25
20
DSL
POGO-II
NAL-RP
15
10
5
0
250
500
1000
2000
4000
Frequency (Hz)
Source: Dillon (2001): Hearing Aids
Hearing threshold (dB HL)
Frequency (Hz)
125 250 500 1k 2k 4k 8k
0
20
40
60
80
Figure 9.5 Same as Figure 9.4, but for a
moderate, flat sensorineural hearing loss.
100
Insertion gain (dB)
120
30
DSL
20
POGO-II
NAL-RP
10
0
250
500
1000
2000
4000
Frequency (Hz)
Source: Dillon (2001): Hearing Aids
Hearing threshold (dB HL)
Frequency (Hz)
125 250 500 1k 2k 4k 8k
0
20
40
Figure 9.6 Same as Figure
9.4, but for a moderate,
steeply sloping sensorineural
hearing loss.
60
80
100
120
70
Insertion gain (dB)
60
50
POGO II
DSL
40
30
NAL-RP
20
10
0
250
500
1000
2000
4000
Frequency (Hz)
Source: Dillon (2001): Hearing Aids
Hearing threshold (dB HL)
Frequency (Hz)
125 250 500 1k 2k 4k 8k
0
20
40
60
Figure 9.7 Same as Figure
9.4, but for a profound,
gently sloping sensorineural
hearing loss.
80
100
120
90
POGO II
Insertion gain (dB)
80
70
DSL
60
NAL-RP
50
40
30
250
500
1000
2000
4000
Frequency (Hz)
Source: Dillon (2001): Hearing Aids
Output (SPL in 2 cc coupler)
soft
average loud
130
IHAFF
prescription
110
Loud
90
Average
Soft
70
50
30
30
50
70
90
110
130
Input dB SPL @ HA Mic
Figure 9.8 An example of the three-point I-O curve, for a frequency of 2 kHz,
prescribed by the VIOLA software on the basis of the IHAFF procedure.
Source: Dillon (2001): Hearing Aids
Fig 6
prescription
Insertion gain (dB)
50
40
40
65
30
20
10
95
0
0 10 20 30 40 50 60 70 80 90
Hearing threshold (dB HL)
Figure 9.9 Insertion gain prescribed by the FIG6 method at
any frequency as a function of hearing threshold, for each of
the three input levels 40, 65, and 95 dB SPL.
Source: Dillon (2001): Hearing Aids
Ear canal output level
(dB SPL)
Basis of
DSL
ULhi
THhi
THn-SFt
ULhi -SFt
Free field input level (dB SPL)
Figure 9.10 The DSL[i/o] method, showing which input levels are mapped to
which output levels, using the terminology from Cornelisse et al. (1995). UL
stands for upper level of comfortable listening, and TH stands for threshold,
where both are expressed in dB SPL in the ear canal. The subscripts n and hi
stand for normal and hearing impaired respectively. SFt is the sound field
transform from free field SPL to ear canal SPL for the unaided ear for the
frequency in question, and is synonymous with REUG.
Source: Dillon (2001): Hearing Aids
Nonlinear
30
prescriptions
IHAFF
50 dB SPL
DSL I/O
20
FIG 6
10
NAL-NL1
0
100
Insertion gain (dB)
30
1000
10000
1000
10000
1000
10000
65 dB SPL
20
10
0
100
20
80 dB SPL
Figure 9.11 Insertion gain
at input levels of 50, 65,
and 80 dB SPL for each of
four selection procedures
for a person with a flat 40
dB hearing loss. The
IHAFF prescriptions are
based on the average
loudness growth curves
for people with various
degrees of hearing loss
(Cox, private
communication). The DSL
[i/o] prescription has been
converted from real ear
aided gain to insertion gain
by subtracting an adult
average REUG.
10
0
100
Frequency (Hz)
Source: Dillon (2001): Hearing Aids
Output (canal dB SPL)
Nonlinear I-O curves
120
Discomfort
100
IHAFF
DSL[i/o]
80
Threshold
FIG6
60
NAL-NL1
IG=0
40
0
20 40 60 80 100 120
Input (field dB SPL)
Figure 9.12. Input-output
diagrams at 2 kHz, showing
the knee-points in the
curves, for the Fig 6, NALNL1, DSL [i/o], and IHAFF
procedures, for a person
with a flat 60 dB HL hearing
loss and a two-channel
compression hearing aid.
The IHAFF procedure is
based on average loudnessgrowth curves. The DSL[i-o]
curve is drawn with the CT
used in its derivation. In
practice a much higher CT
would be used, similar to
that of the other procedures.
Source: Dillon (2001): Hearing Aids
Voltage or Pressure
Compression limiting and peak clipping
Time
Time
Compression Limiting
Peak Clipping
Figure 9.13 A speech waveform after passing through a
peak clipper and a compression limiter, where both types of
limiter can pass the same peak signal level without clipping.
Source: Dillon (2001): Hearing Aids
Three frequency average SPL
(2 cc dB SPL)
150
Estimated
optimum MPO
140
130
OSPL90
prescription
Maximum to avoid
discomfort
120
110
100
90
Minimum to avoid
saturation
80
70
0
20
40
60
80
100
120
Three frequency average HTL (dB HL)
Figure 9.14 The NAL SSPL selection procedure, based on values
midway between the OSPL90 needed to avoid discomfort and the
OSPL90 needed to avoid excessive saturation.
Source: Dillon (2001): Hearing Aids
+
(a)
Volume
control
Compression
limiters
Band gains
+
(b)
Figure 9.15 A multi-channel hearing aid in which limiting occurs (a) independently in each
channel, and, (b) on the wide-band signal after the channels have been recombined.
Source: Dillon (2001): Hearing Aids
Upper aidable
frequency
Frequency (Hz)
125
250
500
1k
2k
4k
8k
Hearing threshold (dB HL)
0
20
40
60
80
100
120
Figure 9.16 Two audiograms with similar losses at 2 and 3 kHz,
but different upper frequency limits of aidable hearing.
Source: Dillon (2001): Hearing Aids