Application of Linux Audio in Hearing Aid Research

Transcription

Introduction and Overview
A Linux-based Hearing Aid
Conclusions
Application of Linux Audio in Hearing Aid
Research
Giso Grimm1
1 Universität
Tobias Herzke2
Volker Hohmann2
Oldenburg, Oldenburg, Germany
2 HörTech
gGmbH, Oldenburg, Germany
Linux Audio Conference, April 17th, 2009.
Giso Grimm, Tobias Herzke, Volker Hohmann
Conclusions
Hearing Aids
Algorithms for Digital Hearing Aids
Evaluation of Hearing Aids
RT performance
CPU and battery performance
Delay Constraints
Conclusions
Conclusions
Hearing Aids
Hearing Aids
Analogue hearing aids
I
Limited capabilities:
I
Frequency shaping and amplification
I
Dynamic compression
I
Static notch filters for feedback cancellation
Conclusions
Hearing Aids
Hearing Aids
Analogue hearing aids
I
Limited capabilities:
I
Frequency shaping and amplification
I
Dynamic compression
I
Static notch filters for feedback cancellation
Digital hearing aids
I
First hearing aid with Digital Signal Processing in 1996
I
New algorithms with no analogue counterpart
Wireless binaural link between ears
I
I
I
Parameter exchange
Coming soon: Low-delay low-power audio transmission
Conclusions
Hearing Aids
Limitations of hearing aids
Device
I
Small battery capacity
I
Low processing power
Acoustics
I
Acoustic feedback
I
Limited audio bandwidth (by tube between receiver and ear)
End user
I
High expenses
I
Unfulfilled expectations
Conclusions
Hearing Aids
Algorithms scalable to individual hearing loss
I
Dynamic compression
I
Frequency shaping
I
Frequency compression
Signal enhancement
I
Directional microphones
I
Noise reduction
Artifact reduction
I
Feedback cancellation
I
Future: Non-linearity compensation, . . .
Conclusions
Hearing Aids
Why dynamic compression?
140
level / dB SPL
120
100
80
I
60
40
20
Normal hearing
threshold
ISO normal HTL
0
50
100
200
500 1k
2k
frequency / Hz
5k
10k
Conclusions
Hearing Aids
140
level / dB SPL
120
100
80
I
Hearing impaired
threshold
I
Amplification and
frequency shaping
typical impaired HTL
60
40
20
0
50
100
200
500 1k
2k
frequency / Hz
5k
10k
Conclusions
Hearing Aids
140
120
level / dB SPL
normal UCL
100
80
I
60
40
Normal
uncomfortable level
20
0
50
100
200
500 1k
2k
frequency / Hz
5k
10k
Conclusions
Hearing Aids
140
level / dB SPL
120
100
typical impaired UCL
80
I
Hearing impaired
uncomfortable level
I
Dynamic compression
60
40
20
0
50
100
200
500 1k
2k
frequency / Hz
5k
10k
Conclusions
Hearing Aids
Directional microphones: SNR improvement
+
−
T
I
Delay-and-sum:
up to 3 dB
SNR-improvement for
on-axis sounds in diffuse
noise
I
Many more beamformers
and direction-of-arrival
estimators
Conclusions
Hearing Aids
Noise reduction and de-reverberation
target signal
S
direct signal
Dl
Dr
I
Single channel noise
reduction
I
Binaural noise reduction,
de-reverberation
I
Binaural coherence
estimation: Interaural phase
difference statistics
Rl
reverberated signal
diffuse noise
Rr
reverberated signal
Nl
Nr
diffuse noise
Xl
Xr
Conclusions
Hearing Aids
Artifact reduction: Feedback cancellation
fbc_wave
A/D
?
I
Adaptive feedback
cancellation
I
Estimation of
feedback signal
I
Subtraction from
input
lms, blms
FNLMS
x(t)
delay
H’(f)
+
−
H(f)
G(f)
generic
HA
D/A
y(t)
Conclusions
Hearing Aids
Artifact reduction: Feedback cancellation
fbc_wave
A/D
?
I
Adaptive feedback
cancellation
I
Estimation of
feedback signal
I
Subtraction from
input
I
Other solutions:
Frequency shifting,
phase modulation,
binaural coherence
lms, blms
FNLMS
x(t)
delay
H’(f)
+
−
H(f)
G(f)
generic
HA
D/A
y(t)
Conclusions
Hearing Aids
Expected benefit of hearing aids
I
Improvement of speech intelligibility
I
Reduction of listening effort in adverse listening conditions
I
Increase of listening comfort
Conclusions
Hearing Aids
Expected benefit of hearing aids
I
Improvement of speech intelligibility
I
Reduction of listening effort in adverse listening conditions
I
Increase of listening comfort
Evaluation is required!
Conclusions
Hearing Aids
Evaluation methods
’Objective’ methods
I
SNR improvement (e.g., shadow filtering)
I
Speech intelligibility index (f -weighted SNR)
I
Quality prediction (usually similarity measures)
Subjective methods
I
Speech recognition threshold in quiet and noise
I
Quality rating, paired comparison ...
Conclusions
Hearing Aids
Test conditions
I
’static’ situations:
no spatial influecnce, pre-processed or real-time procesing
I
dynamic conditions:
head movements or moving sources, real-time processing
I
realistic devices, acoustic feedback:
low-delay real-time processing
I
Real-life conditions:
wide dynamic range, portable low-delay real-time processing
Conclusions
Hearing Aids
Real-time systems
1995: PC with DSP board, assembler programming
Conclusions
Hearing Aids
Real-time systems
2000: Portable DSP board, assembler programming
(DASi, U. Rass 2001)
Conclusions
Hearing Aids
Real-time systems
2008: Portable PC, C++ (or Matlab) programming
Conclusions
RT performance
Delay Constraints
A Linux Hearing Aid
Conclusions
RT performance
Delay Constraints
A Linux Hearing Aid
for research, development and field testing
Conclusions
RT performance
Delay Constraints
The ’Master Hearing Aid’ software
I
Platform for hearing aid algorithm development and evaluation
I
Many audio backends: JACK, ALSA (Linux), ASIO
(Windows), file, network, Matlab
I
Extremely modular structure
I
Hearing-aid (and hearing) related processing blocks
I
Commercial product (closed source) by HoerTech gGmbH,
Oldenburg
I
Used in research projects and hearing aid industry
Conclusions
RT performance
Delay Constraints
Licensing in competitive research
I
Industrial/competitive context often requires closed-source
development
I
Industry decision makers fear the open source licensing of
Linux
I
It is possible to develop closed software on the Linux platform
without infringing any licenses!
I
Careful consideration of what components to use
I
Knowledge of the relevant licenses, and compliance with their
terms.
I
Use of open source software in industrial context benefitial for
both sides
Conclusions
RT performance
Delay Constraints
Comparison of RT kernel versus non-RT kernel
normal scheduling
time per cycle / ms
0.2
0.18
0.16
0.14
0.12
0.1
0
500
1000
1500
2000
1500
2000
real−time scheduling
time per cycle / ms
0.2
0.18
0.16
0.14
0.12
0.1
0
500
1000
fragment number
Kernel version 2.6.X (2.6.23?), from Grimm et al. (2006)
Conclusions
RT performance
Delay Constraints
RT performance and low-delay
1.2
real−time ratio
1
0.8
0.6
8 channel DC
1 channel DC
identity, spectrum
identity, waveform
0.4
0.2
0
2 3 4 5 6 7 8 9 10 11 12 13 14 15
log2(fragsize)
Algorithm implementation in
C/C++
Conclusions
RT performance
Delay Constraints
1.2
1.2
1
1
0.8
0.6
8 channel DC
1 channel DC
identity, spectrum
identity, waveform
0.4
0.2
0
real−time ratio
real−time ratio
RT performance and low-delay
0.8
0.6
0.4
0.2
2 3 4 5 6 7 8 9 10 11 12 13 14 15
log2(fragsize)
C/C++
0
8−channel DC
8 1−channel DC
1−channel DC
identity, spectrum
identity, waveform
2 3 4 5 6 7 8 9 10 11 12 13 14 15
log2(fragsize)
Matlab
Conclusions
RT performance
Delay Constraints
CPU and batttery performance
I
Two portable systems
I
Asus Eee PC 701:
Intel Celeron @ 630 MHz
I
Acer Aspire one:
Intel Atom @ 1.6 GHz
I
Reference Desktop system (Intel P4 @ 3GHz)
Conclusions
RT performance
Delay Constraints
Comparison of CPU performance
70
IRQ
jack
MHA
algo
60
CPU load in %
50
40
30
20
10
0
4
go
al 3
go
al 2
go
al 1
go
Acer Aspire One
al
4
go
al 3
go
al 2
go
al 1
go
al
4
go
al 3
go
al 2
go
al 1
go
al
Asus Eee PC 701
Desktop P4
Conclusions
RT performance
Delay Constraints
Comparison of batteries
3h30’
battery runtime
3h15’
3h00’
2h45’
2h30’
2h15’
2h00’
4
go
3
go
al
al
2
go
al
1
go
al
4
go
3
go
al
2
go
al
al
1
go
al
Asus Eee PC 701
Acer Aspire One
Conclusions
RT performance
Delay Constraints
Delay Constraints
Three sources of delay in RT processing
I
Block processing delay:
Fragment size plus processing delay
(i.e., two blocks if input and output is block aligned)
I
Hardware delay:
Anti-aliasing filter (AD and DA, typical 1.5 ms in total)
Data transmission, driver layer (’mystic’ delays)
I
Algorithmic delay:
Group delay of filters, overlap-add delay, . . .
Conclusions
RT performance
Delay Constraints
Why do we aim for lowest delay? ⇒ Feedback howling
I
Feedback criterion: Roundtrip-gain is above 0 dB, and phase
is multiple of 2π
Conclusions
RT performance
Delay Constraints
Why do we aim for lowest delay? ⇒ Feedback howling
20
0
−20
phase (1 ms)
OLG + 20 dB
Feedback criterion: Roundtrip-gain is above 0 dB, and phase
is multiple of 2π
phase (5 ms)
I
0.5
1
0.5
1
0.5
1
2
4
8
2
frequency / kHz
4
8
2
frequency / kHz
4
8
pi
0
−pi
pi
0
−pi
Conclusions
RT performance
Delay Constraints
Achievable delays
Device
Echo Layla 3G
RME HDSP9652 +
Behringer SRC2496
RME HDSP9652 +
Behringer ADA8000
RME HDSP9632 +
ADI8QS
OFFIS
USB SC-4/2
fs /kHz
32
44.1
100
32
44.1
96
32
44.1
44.1
96
16
44.1
96
fragment size
32
64
32
64
64
128
64
64
64
128
16
64
128
τsc /ms
2.81
2.04
0.81
3.34
2.68
1.73
2.13
1.61
1.52
1.03
6.81
4.08
1.97
τt /ms
4.81
4.94
1.77
7.34
5.58
4.40
6.12
4.51
4.42
3.7
9.81
8.44
5.97
Conclusions
Device
Echo Layla 3G
RME HDSP9652 +
Behringer SRC2496
RME HDSP9652 +
Behringer ADA8000
RME HDSP9632 +
ADI8QS
OFFIS
USB SC-4/2
fs /kHz
32
44.1
100
32
44.1
96
32
44.1
44.1
96
16
44.1
96
RT performance
Delay Constraints
fragment size
32
64
32
64
64
128
64
64
64
128
16
64
128
τsc /ms
2.81
2.04
0.81
3.34
2.68
1.73
2.13
1.61
1.52
1.03
6.81
4.08
1.97
τt /ms
4.81
4.94
1.77
7.34
5.58
4.40
6.12
4.51
4.42
3.7
9.81
8.44
5.97
Conclusions
Device
Echo Layla 3G
RME HDSP9652 +
Behringer SRC2496
RME HDSP9652 +
Behringer ADA8000
RME HDSP9632 +
ADI8QS
OFFIS
USB SC-4/2
fs /kHz
32
44.1
100
32
44.1
96
32
48
44.1
96
16
44.1
96
RT performance
Delay Constraints
fragment size
32
64
32
64
64
128
64
64
64
128
16
64
128
τsc /ms
2.81
2.04
0.81
3.34
2.68
1.73
2.13
1.46
1.52
1.03
6.81
4.08
1.97
τt /ms
4.81
4.94
1.77
7.34
5.58
4.40
6.12
4.12
4.42
3.7
9.81
8.44
5.97
Conclusions
Device
Echo Layla 3G
RME HDSP9652 +
Behringer SRC2496
RME HDSP9652 +
Behringer ADA8000
RME HDSP9632 +
ADI8QS
OFFIS
USB SC-4/2
fs /kHz
32
44.1
100
32
44.1
96
32
44.1
44.1
96
16
44.1
96
RT performance
Delay Constraints
fragment size
32
64
32
64
64
128
64
64
64
128
16
64
128
τsc /ms
2.81
2.04
0.81
3.34
2.68
1.73
2.13
1.61
1.52
1.03
6.81
4.08
1.97
τt /ms
4.81
4.94
1.77
7.34
5.58
4.40
6.12
4.51
4.42
3.7
9.81
8.44
5.97
Conclusions
Device
Echo Layla 3G
RME HDSP9652 +
Behringer SRC2496
RME HDSP9652 +
Behringer ADA8000
RME HDSP9632 +
ADI8QS
OFFIS
USB SC-4/2
fs /kHz
32
44.1
100
32
44.1
96
32
44.1
44.1
96
16
44.1
96
RT performance
Delay Constraints
fragment size
32
64
32
64
64
128
64
64
64
128
16
64
128
τsc /ms
2.81
2.04
0.81
3.34
2.68
1.73
2.13
1.61
1.52
1.03
6.81
4.08
1.97
τt /ms
4.81
4.94
1.77
7.34
5.58
4.40
6.12
4.51
4.42
3.7
9.81
8.44
5.97
Conclusions
RT performance
Delay Constraints
Demonstration now!
Conclusions
Conclusions
I
Hearing aid research is a wide field and requires careful
evaluation.
I
Linux Audio provides a valuable environment for hearing aid
research.
I
Low delay processing is possible with Linux/ALSA/Jack
(but mystic delays remain in the chain of soft- and hardware).
Conclusions
Thank you for your attention!

Application of Linux Audio in Hearing Aid Research

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