Figures for Chapter 5 Earmolds and earshells Dillon (2001) Hearing Aids.
Figures for Chapter 6 Compression Dillon (2001) Hearing Aids.
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Transcript of Figures for Chapter 6 Compression Dillon (2001) Hearing Aids.
Figures for Chapter 6
Compression
Dillon (2001)
Hearing Aids
Figure 6.1 Three ways in which the dynamic range of signals can be reduced. In each case, the upper figure shows the spacing of different signal levels before amplification (the left end of the lines) and after amplification (the right end of the lines). The lower figure shows the same data, but as an input-output function.
Ou
tpu
t Le
vel
Weak Moderate Intense
Out
put L
evel
Weak Moderate Intense
Wide Dynamic RangeHigh Level Low Level
Ou
tpu
t Le
vel
Weak Moderate Intense
Input level
Source: Dillon (2001): Hearing Aids
Varieties of compression
Time
Output:
Input:
Pressure
Figure 6.2 Waveforms that are input to a compressor and output from a compressor, showing the attack and release transitions that follow an increase and decrease, respectively, in signal level. The dotted line shows the envelope of the positive half of the signal.
Source: Dillon (2001): Hearing Aids
Compression waveforms
Ta = 0.1Ts
Tr = 0.3 Ts
Fast
Ta= Tr = 10Ts
Slow
Ta = Tr = Ts
Medium
Linear
Ts
Figure 6.3 Envelopes for the output signal coming from a linear amplifier and compression amplifiers with different attack times (Ta), and release times (Tr) compared to the duration of each syllable (Ts) in the signal.
Source: Dillon (2001): Hearing Aids
Compressed envelopes
Figure 6.4 A block diagram of a feedforward, look-ahead compression control circuit.
Delay
Detector
Source: Dillon (2001): Hearing Aids
Feedforward compression
80
90
100
110
120
130
30 40 50 60 70 80 90 100
Input Level (dB SPL)
Ou
tpu
t Le
vel (
dB
SP
L)
I
O
Compression range
2 dB
LinearLimiting
Linear
20
30
40
50
60
30 40 50 60 70 80 90 100
Input Level (dB SPL)
Ga
in (
dB)
Figure 6.5 Upper: input-output diagram showing the definition of several static compression characteristics. Lower: the graph of gain versus input that corresponds to the I-O curve above it.
Source: Dillon (2001): Hearing Aids
I-O curve and
gain-input curve
80
90
100
110
120
130
30 40 50 60 70 80 90 100 110
Input Level (dB SPL)
Out
put
Le
vel (
dB S
PL
)
Figure 6.6 Input-output characteristics corr-esponding to curvilinear compression(solid line) and a fixed compression ratio combined with compression limiting (dashed line).
Source: Dillon (2001): Hearing Aids
Cuvilinear compression
Figure 6.7 Input controlled compression and output controlled compression: their block diagrams and the I-O curves for each as the volume control is varied from maximum to minimum positions.
Input controlled compression
F
Output controlled compression
F
Input (dB SPL)
Out
put
(dB
SP
L)
40 50 60 70 80 90 100 110
80
70
60
50
40
90
100Vol max
Vol min
Input (dB SPL)
Out
put
(dB
SP
L)
80
70
60
50
40
90
100
40 50 60 70 80 90 100 110
Vol min
Vol max
Source: Dillon (2001): Hearing Aids
30
50
70
90
110
Leve
l (dB
)
(a)
-20
0
20
Gain
(dB
)
(b)
30
50
70
90
110
Leve
l (dB
)
(c)
-20
0
20
Time
Ga
in (
dB
)
(d)
Figure 6.8 (a) Envelope of the signal The yellow flower has a big bud put into the hearing aid at two levels. The thick curve shows the envelope for linear amplification and the thin red curve shows the envelope for a compressor with a 3:1 compression ratio, attack time of 20 ms, and release time of 200 ms. Part (b) shows the gain applied by the compressor. Part (c) shows the envelope for linear amplification and for compression when the attack and release times of the compressor were increased to 1000 and 2000 ms respectively. The corresponding gain is shown in part (d).
Source: Dillon (2001): Hearing Aids
Linear and compressed envelopes
40
50
60
70
80
90
100
110
30 40 50 60 70 80 90 100 110
Input Level (dB SPL)
Out
put
Leve
l (dB
SP
L)
Linear
Medium levelcompression
WDRC
Figure 6.9 Input-output curves for medium level compression, wide dynamic range compression, and linear amplification, all combined with either compression limiting or peak clipping of high level signals.
Source: Dillon (2001): Hearing Aids
0 20 40 60 80 100
Loud
ness
cat
egor
y
Very Soft
Comfortable
Uncomf. loudNormal
Impaired
SoftComf, slightly soft
Comf, slightly loudLoud but OK
10
30
50
0 20 40 60 80 100
Inse
rtio
n ga
in (
dB)
50
70
90
110
0 20 40 60 80 100
Input level (2cc dB SPL)
Out
put
leve
l (
dB S
PL)
Figure 6.10 (a) Loudness growth curves for normal hearing people and a hearing impaired person with a 50 dB hearing loss. (b) Insertion gain needed for the impaired listener to receive a normal loudness sensation. (c) The corresponding I-O curve.
Source: Dillon (2001): Hearing Aids
Loudness normalization
Figure 6.11 Block diagrams of (a) two-channel and (b) single channel processing schemes that can implement approximations of loudness normalisation, and (c) the resulting typical TILL gain-frequency response that increases in slope as the input level decreases from 90 to 50 dB SPL.
+
(a)
(b)
-100
102030405060
0.1 0.2 0.5 1.0 2.0 5.0Frequency (kHz)
Gai
n (d
B)
50
90
(c)
Source: Dillon (2001): Hearing Aids
Loudness normalization
(TILL)
Figure 6.12 (a) Spectrum of the signal and noise input to a noise reduction hearing aid. (b) Gain applied to the signal and noise. (c) Spectrum of the signal and noise at the hearing aid output.
Gai
n (b)
Noise
Out
put
Spe
ctra
lLe
vel
Frequency
Signal
1 kHz
(c)
Inpu
t S
pect
ral
Leve
lSignal Noise
Possible masking
(a)
Source: Dillon (2001): Hearing Aids
Noise reduction
Figure 6.13 Block diagrams of two-channel and single-channel processing schemes that can implement simple noise reduction strategies, and the resulting BILL response that decreases in slope as the input level decreases from 90 to 50 dB SPL.
0.1 0.2 0.5 1.0 2.0 5.0Frequency (kHz)
-10
10
30
50
Gai
n (d
B)
50
90
+
Source: Dillon (2001): Hearing Aids
Noise reduction (BILL)
Input level
Out
put
leve
lLinear
Compression
70
InputRange
Out
put
ran
ge
Figure 6.14 Input-output functions for two different hearing aids adjusted to have the same output for a 70 dB SPL input signal.
Source: Dillon (2001): Hearing Aids
Output levels