Sound Coding Strategies for Cochlear- Implants · 30 years of cochlear implant experience World largest cochlear implant programm (7000 Impl. 2013) 500 patients are implanted every

Sound Coding Strategies for Cochlear-

Implants

Waldo Nogueira Auditory Prosthetic Group, Department of Otolaryngology, Medical University Hannover

Many Slides from Prof. Andreas Büchner and Tobias Rottmann

Slides and Materials available under: http://auditoryprostheticgroup.weebly.com/blog

Auditory Prosthetic Group

APG

Waldo Nogueira

Benjamin Krüger

Marina Frye

Florian Langner

APG, http://auditoryprostheticgroup.weebly.com

• Goals APG

– Improve speech intelligibility in noise and music perception with

cochlelar implants

• How? Two possibilities

– Technology: Modify the Cochlear Implant Sound Processor

– Art: Create contents specific for Cochlear Implant users

Auditory Prosthetic Group (APG)


Characterize

the Electrode-

Nerve-Interface

Subjective

Responses

Psychophysical

Measures

Individualize

Parameteres

(Noise Reduction)

Goal: Optimize Individually

Speech Intelligibility and

Music Perception for CI users

Technology: Personalization

State-Of-the Art

Signal Processing

(Noise Reduction)


APG:

Auditory Prosthetic Group

5

Research (H4A, Auditory Prosthetic Group) The group started in September 2013 as part of Excellence

Cluster Hearing4all

Covering fields Signal processing

Auditory modelling applied to implanted hearing protheses Cochlear implants and electroacoustic stimulation implants

Psychophysics

Electrophysiology

Department Otoloringology/German Hearing Center 30 years of cochlear implant experience

World largest cochlear implant programm (7000 Impl. 2013)

500 patients are implanted every year

Large spectrum of Hearing Systems Cochlear-Implants, Middle Ear Implants, Heraing Aids

ABI (auditory brainstem implant), AMI (auditory midbrain implant)

0

50

100

150

200

250

300

350

400

1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

Patientenzuwachs an der MHH

Verlauf von 1984 bis 2013

(Erw=2858 Kinder=2294)

Erwachsene Kinder

Number of CI-Implantations at MHH

0

100

200

300

400

500

600

1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

Implantzahlen nach Implanttyp

Verlauf von 1984 bis 2013

Nucleus=4107 AB=2081 Medel=726 Digisonic=3

N = 6944

Nucleus AdvBionics MedEl Digisonic Reimplantationen

-300 -200 -100 0 100 200 300

1

4

7

10

13

16

19

22

25

28

31

34

37

40

43

46

49

52

55

58

61

64

67

70

73

76

79

82

85

88

91

Age distribution at implantation time

Woman Man

Medizinische Hochschule

Hannover

8

Audiology

Surgery

(HNO)

DHZ (German Hearing

Center) APG

Contents

1. Introduction

2. Fundamentals of electric stimulation

3. Historical overview of sound coding strategies

4. Current sound coding strategies

5. Summary

The Cochlear Implant

Hybrid Hearing Aid

and

Cochlear Implant

The Cochlear Implant

The Cochlear-Implant – An electronic innear ear prosthesis

Implant Speech processor

Fa. Medel

Advanced

Bionics

USA

Neurelec/Oticon

France

MEDEL

Austria

Cochlear

Australia

CI-Manufacturers and current models at the MHH

Other CI-Manufactuters

Cochlear-Implantat-System: IES (= „I Enjoy Sound“)

Cochlear-Implant-System from a chinese manufacturer: Nurotron

Hearing performance with a cochlear-implant

0

10

20

30

40

50

60

70

80

90

100

FES HSM in quiet HSM im noise

% c

orr

ect

n=480

Duration of deafness < 10 Years

Newest generation implant (all

manufacturers)

Column of Volta (around 1800)

Alessandro Volta (1745 – 1824)

- Inserted in the ear canal a solution of salt water and

inserted a voltage through two electrodes of its own

developed battery

- Discovered the battery.

- Hearing perception described as: „Dense soup

being cooked“.

Alessandro Volta

http://upload.wikimedia.org/wikipedia/commons/5/52/Alessandro_Volta.jpeg

Charles Eyriès

Charles Eyriès & André Djourno (1957)

First “Cochlear-Implantat”

im Humans

André Djourno

The otologist Eyriès and der physicist Djourno from Paris

placed electrodes on the trunk of the auditory nerve using

primitive electrodes with a primitive speech stimulator.

They were able to create hearing sensations.

Simple

induction coil

for implants

The implanted coil

William House (1923 – 2012), in 1970 (3M Implant)

William House Jack Urban (right) 3M Single-

Electrode Implant

Single Electrode Cochlear-Implantate

Amplifier

340 bis 2700 Hz

Bandpass Microphone Modulation Electrode

AM Carrier 16kHz

Single Electrode Cochlear-Implantate

Zeng 2004

Speech I

nte

lligib

ility

in Q

uie

t [%

] Speech Intelligibility

Multichannel Cochlear-Implant

Graham Clark (right) The first multichannel cochlear implant


The goal of a speech processing strategy consists of decomposing the frequency,

time and loudness information of the acoustic sound to create electric signals that

stimulate the auditory nerve.

Clark Feature Extraction 1978


The first speech processor for the multichannel cochlear implant system



The first body worn speech processor for the multichannel cochlear implant

system

Contents

1. Introduction




5. Summary

Sound capturing and transmission

Boenninghaus, Lenarz:

Hals-Nasen-Ohren-Heilkunde, 2007

Scala vestibuli

Scala tympani Ductus cochlearis

Elektrode

Standard (31 mm)

FLEXSOFT (31 mm)

FLEX28 (28 mm)

FLEX24 (24 mm)

FLEX20 (20 mm)

Medium (24 mm)

Compressed (15 mm)

Contour Advance

Slim Straight

Straight

Hybrid L24

Cochlear (22 Contacts) MEDEL (12 Contacts)

Advanced Bionics (16 Contacts)

Electrode arrays

Stimulation modes

Büchner (2004)

Ball

Electrode

Case

Electrode

Electrode Carrier

Stimulation mode

Monopolar Stimulation

- One intracochlear electrode is connected to an extracochlear reference

electrode such that the corrent flows between both electrodes.

- A simultaneous stimulation of multiple electrodes at the same time is not

desirable because undesirable channel interaction between the individual

electrodes would arise.

Büchner (2004)

Stimulation modes

Bipolar Stimulation

- Here the active electrode and the reference electrode are both

intracochlear.

- If the implants has multiple current sources it is possible to stimulate

multiple channels with moderate channel interaction.

- The more distant are the stimulating and the reference electrodes, the

louder is the hearing perception because a larger number of nerve fibers

is stimulated.

Büchner (2004)

Stimulation modes

Common Ground Stimulation

- Here one intracochlear electrode is stimulated against all other

intracochlear electrodes, which are used as reference electrodes.

- This stimulation mode has been substituted by the simple monopolar

mode which offers power savings without decreasing speech

performance.

Büchner (2004)

Stimulation with biphasic pulses

+

-

Pulse width - The amount of charge defines the

loudness (Pulse width and amplitude)

Am

plit

ude

- Stimulation rate (or. Pulse rate)

- The charge density has to be limited (it

depends on the injected charge and the

electrode dimensions)

Pulse distance Stimulationsrate

- Charge balanced pulse

Stimulation with biphasich pulses

+

Pulse width - The amount of charge defines the

loudness (Pulse width and amplitude)

Am

plit

ude

- Stimulation rate (or. Pulse rate)

- The charge density has to be

limited (it depends on the injected

charge and the electrode

dimensions)

- Charge balanced pulse

This can cause an irreversible reaction in the surrounding of the electrode,

including changes in the pH-value, release of part of the electrode material and

forming of metal-protein complexes.

-

Pulse distance Stimulation rate

Electrode-Impedance Interface

ρ : resistivity

: Dielectric constant

: Electric field constant

Current flow inside the cochlea

Klinke & Hartmann (1979)

Stromfluss innerhalb der Cochlea

Tang (2011)

Simulation of the voltage distribution in the cohlea

Nogueira (2014)

Monopolar Stimulation:

Acoustic vs. electric stimulation

Normal Hearing

Hearing with

CI

high

reduced high Synchronicity

Spontaneous activity

120 dB 12 dB Dynamic range

3500 IHC ~10 channels Frequency resolution

simultaneous coding Temporal stimulation pattern

Processing of new signals through the auditory system required

missing

narrow Spatial stimulation specificy wide

Contents

1. Introduction




5. Summary

t

Envelope

Hilbert 1912: Signal decomposition

in fast + slow oscilating components

Fine structure

Speech

Pitch & Localization

Acoustic Phonetic – Vocal formants

Jussen et al., 1994

F3

F2

F1

F0F2 (beginning of 1980‘s)

AGC

Pulse-

generator

1000 4000 Hz

F2 Zero-cross

Envelopes A2

270 Hz

F0 Zero-cross Pulse-

rate

/a/

F0 = 140 Hz

F0F2 (beginning of 1980‘s)

- The fundamental frequency of the speaker (F0 < 280 Hz) is used as stimulation

rate

- Selection of the stimulating electrodes depends on the frequency of the second

formant (between 800 und 4000 Hz)

- The stimulation current is proportional to the estimated amplitude of the 2.

Formant

- Only one electrode is stimulated for each stimulating cycle

- Cleary, this strategy is designed to encode speech signals

Characteristics of the F0F2-Strategy:

F0F1F2 (1985)

AGC

Pulse-

generator

280 1000 Hz

F1 Zero-cross

Envelope A1

1000 4000 Hz

F2 Zero-cross

Envelope A2


rate

/a/

270 Hz

F0F1F2 (1985)

Characteristics of the F0F1F2-Strategy:

- The fundamental frequency of the speaker (F0 < 280 Hz) is used as stimulation

rate

- Electrodes 1 to 5 are used to transmit the 1. Formant (between 280 und 1000

Hz)

- Electrodes 6 to 20 are used to transmit the 2. Formant (between 1000 und 4000

Hz)

- Two electrodes are stimulated in each processing cycle

- The stimulation current is proportional to the 1. und 2. Formants

- Cleary, this strategy is designed to encode speech signals

MPEAK (End 1980‘s)

AGC

Pulse-

generator

300 1000 Hz

F1 Zero-cross

Envelope A1

800 4000 Hz

F2 Zero-cross

Envelope A2

270 Hz


rate

2 2,8 kHz

Envelope

2,8 4 kHz

Envelope

4 6 kHz

Envelope Electrode 1

Electrode 4

Electrode 7

1 4

7

F1

F2

MPEAK (Ende 1980er)

Characteristics of the MPEAK-Strategy (Multipeak-Strategy):

- The strategy is based on the F0F1F2-Strategy (Useful to recognize vowels)

- Introduces three high frequency filters:

- The problem of erroneous feature extraction persists

Stimulation electorde Frequency region

7 2-2,8 kHz

4 2,8-4 kHz

1 4-4,7 kHz

Compressed Analog (CA)

Amplifier

100 700 Hz

Bandpass Michrophone Electrodes

700 1400 Hz

1400 2300 Hz

2300 5000 Hz

G1

G2

G3

G4

AGC

Characteristics of the CA-Strategy:

- Four band-pass filters between around 300 until 5000 Hz

- Simultaneous stimulation of four intracochlear electrodes

- Monopolar stimulation (later improved through bipolar stimulation)

- Better than a single electrode system

- Better performance than the F0F2 Strategy

- Problem: Strong channel interaction => Addition of neighbouring

channels

Compressed Analog (CA)

Zeng 2004

Speech inte

lligib

ility

in q

uie

t [%

] Speech intelligibility

CIS (Beginning of 1990‘s)

AGC

n

A1

A2

A3

1

2

3

An

Continuous Interleaved Sampling

CIS (Anfang 1990er)

Characteristics of the CIS-Strategy as implemented by the Advanced Bionics

Systems (Clarion):

- 8 Bandpassfilters from 250 unitl 5500 Hz

- 60 dB dynamic range => It is compressed/mapped into the patient specific

electric dynamic range

- Stimulation with biphasic squared pulses with a pulse width of 75µs/Phase

- The stimulation rate for each electrode is around 833 Hz

- It is based on a similar principle as the Vocoder from Dudley (see next slide)

The Vocoder from the Bell Laboratories (H. Dudley, 1939)

Bell Labs Records, Dec. 1939

10 Channel– Vocoder (H. Dudley 1939)

Example with fundamental frequency Example without fundamental frequency

Frequency bands as used by the MEDEL-Systems

Compression example as used by the MEDEL-Systems

120

0

Sound pressure

level [dB SPL]

Normal hearing / Acoustic Cochlear-Implantat / Electric

Current

ampltiude [µA]

THL: threshold level

MCL: most

comfortable level

100

400

Pre-processing

12 dB 120 dB 40-65 dB

Signal input in the pre-processing

SPEAK (Begining of 1990‘s)

AGC

20

A1

A2

A3

1

2

3

250 Hz

A20

10000 Hz

Selection

of the 5-

10 largest

A

Compression

Spectral Peak

„n-of-m“

Maxima selection

500 1000 1500 2000 2500 3000 3500 4000 4500 5000 0 5500 Frequenz [Hz]

500 1000 1500 2000 2500 3000 3500 4000 4500 5000 0 5500 Frequenz [Hz]

-5

0

10

20

26

20

10

/eh/

Inte

nsity [d

B]

Inte

nsity [d

B]

SPEAK (Begining of 1990‘s)

- Larger frequency range (250 until 10000 Hz)

- 20 channels

- Only the 5 to 10 channels with the largests energies (maxima) are

selected for stimulation.

(The amount of information to be transmitted to all electrodes would require too much time

reducing the stimulation rate)

- Stimulation rates up to 250 Hz (limited by the technology of the Mini-22

implant)

Characteristics of the Speak-Strategie:

Zeng 2004

Speech inte

lligib

ility

in q

uie

t [%

] Speech intelligibility

ACE (Mitte 1990er)

AGC

22

A1

A2

A3

1

2

3

250 Hz

A22

8000 Hz

Auswahl

der 1-16

größten A

Kompression

Advanced Combination Encoder

Modified SPEAK strategy

- more channels

- higher rates

Speech intelligibility

Zeng, Trends In Amplification 2004:8:1-34

Speech inte

lligib

ility

in q

uie

t [%

]

Er hat heute einen Arzttermin.

Ist das Flugzeug gestartet?

F0/F2 ACE

Example: F0/F2 and „ACE“

F0F2 (in noise)

Osciloscope picture taken with and 8

Channel CIS (AB)

833 pps

Detector box for the MEDEL-System

Output of implant circuits:

Example: CIS and „n of m“

Lower frequencies

Higher frequencies

How is the CI configured in the clinical routine?

Basis Parameter:

- Comfortable (C) Level: The maximum current level that is not

perceived as unpleasant.

- Threshold (T) Level: The lowest current level, that is just perceived.

- Dynamic Range: Difference between the C- and T- level

Low frequency High frequency

Electrode Array

Implant

Dynamic Range

C-Levels

T-Levels

DR = 19-40 CL

120

0

Sound pressure

level [dB SPL]

Normal hearing/ Acoustic Cochlear-Implantat / Electric

Current level

[µA]

THL: threshold level

MCL: most

comfortable level

100

400

Pre-processing

12 dB 120 dB 40-65 dB

Signal input and Pre-processing

Contents

1. Introduction




5. Summary

-ACE & PACE/MP3000 (Cochlear)

-HiRes, HiRes 120 & HiResOptima (Advanced Bionics)

-FSP & FS4 (Med-El)

Current Speech coding strategies

Problem of low bandwidth in a Cochlear-Implant System

Cochlear-Implantat System : 10 - 60 kbit/s

Electrode / Nerve

Interface

Audio-Signal

auditorisches

System ??

700 kBit

One possible solution: Relevant data reduction

Relevant

Signal components

Audio-Signal

Redundant

Auditory

System

Elektrode / Nerve

Interface

The multimedia industry has successfuly implemented psychoacoustic models

for many years.

Motivation for the use of a psychoacoustic masking model

MP3 Player Apple‘s iPod

Reduction of the data volume by 1/10 !

Other channel selection strategies

Simultaner Maskierungeffekt

Hörschwelle

in Ruhe

80

60

40

20

0

2 0 4 6 8 10 12 14

Frequenz [kHz]

Lauts

tärk

e [

dB

]

Hörschwelle bei Präsentation

eines Sinustons 4 kHz 60dB

ACE PACE MP3000 (2005)

AGC

22

A1

A2

A3

1

2

3

250 Hz

A22

8000 Hz

Selection

of 1-6

non-

masked

A

Compression

Nogueira et al., Eurasip, 2005

Speech intelligibility

37 CI-Centers, more than 200 Patients

Büchner et al., 2011

• MP3000 not better than ACE

• Significantly less current consumption than MP3000

„Spectral Contrast Enhancement“ in CI sound coding strategies:

Improvement of the spectral contrast

Nogueira et al., JASA, (2014)

Ma

gn

itu

de

[d

B]

Electrode

original enhanced

22 20 18 16 14 12 10 8 6 4 2

-130

-120

-110

-100

-90

Improvement of the spectral contrast

„Spectral Contrast Enhancement“ in CI Stimulation strategies:

Nogueira et al., JASA, (2014)

Original ACE SCE

-ACE & MP3000 (Cochlear)


-FSP & FS4 (Med-El)

Current speech coding strategies

1

2

3

4

5

6

7

8

1

2

3

4

5

6

7

8

Development stages for an 8 channel sytem of Advanced Bionics

Continuous Interleaved

Sampler – CIS Simultaneous Analogue

Stimulation – SAS

Multiple Pulsatile

Stimulation – MPS o. PPS

from CIS to HiRes

Stimulation rate [pps]

1970 1980 1990 2000 2010 2020

100 250 800 1500 3000 5000

t

A

Compliance-Limit

PW Charge Q = A0 PW

A0

Refractoriness: 1 ms = 1000 pps

0

10

20

30

40

50

60

70

80

90

100

FreiburgerMonosyllabics

FreiburgerNumbers

HSM in quiet HSM in noise

% c

orr

ec

t

SAS user (n=23)

standard mode High Resolution Mode

0

20

40

60

80

100

120


FreiburgerNumbers


% c

orr

ec

t

CIS user (n=21)


0,00

20,00

40,00

60,00

80,00

100,00

120,00


FreiburgerNumbers


% c

orr

ec

t

PPS user (n=2)


Improved Hearing Performance with HiRes

HiRes120 with „Current Steering“

16 Electrode-Contacts 15 current steering-Fields

16 Channels 120 Channels

1 16 2 3 4 5 6 7 8 9 10 11 12 13 14 15

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

HiRes120: HiRes:

HiRes120 with „Current Steering“

Current Steering Music examples

Original 16 Channels 64 Channels

Speech test results

HiRes vs. HiRes 120 => only minimally better than HiRes

Brendel et al., 2008

From HiRes120 to HiRes Optima

The current goal is to develop low power consumption sound coding

strategies keeping hearing performance:

RF Link

Reduction of the supply voltge of the implant from

around. 8V to 4V

Fitting of the pulse parameter to the new supply

voltage

Always use a virtual electrode (Current Steering)

HiRes Optima – Reduced Supply Voltage

Current Steering with HiRes Optima

HiRes 120 HiRes Optima

HiRes Optima

-ACE & MP3000 (Cochlear)


-FSP & FS4 (Med-El)

Current speech coding strategies

Frequency analysis in the cochlea

Place principle: Periodicity principle:

Boenninghaus, Lenarz:

Hals-Nasen-Ohren-Heilkunde (2007) Hellbrück, Ellermeier: Hören (2004)

FSP

Channel-Specific Sampling

Sequences CSSS

Fine Structure Processing

Fa. Medel

CIS

MEDEL Fine structure-Strategy FSP

CIS-channels with

transmission of the envelepe

Stimulation pattern with individual electrode channels:

2 to 4 fine structure

channels (information up

to around 1000 Hz)

Fa. Medel

Speech test results

Müller et al., 2012

With FSP only minimally better than with CIS+/HDCIS

Hearing performance with a Cochlear Implant

0

10

20

30

40

50

60

70

80

90

100

FES HSM in Quiet HSM in Noise

% c

orr

ect

n=480

Duration of deafness < 10 years

Implant with the newest generation (all

manufacturers)

“An ocean of sounds…”

Alex Katz, The Cocktail Party, 1965.

Signal input and preprocessing

1. Signal input /

Mikrophone

technik

2. Signal pre-

processing

Example: Noise reduction

- Clear Voice (AB)

- Noise Canceller (AB & Phonak)

- Noise-Function (Cochlear)

Single channel noise reduction:

Clear Voice und Noise Canceller

• Single-microphone-system (omnidirectional)

• Channel specific analysis of the amplitude modeluation of the signals

• Assumption: Speech (Target signal) has an amplitude modulation of around 2 until 6 Hz.

• Reduces amplification (Gain) in each channel were less modulation is estimated, because this part is considered to not be speech.

=> Effectiv method in stationary noise

Adaptive directional microphone from Phonak

=> Effective in fluctuating background noises

Directional dependent amplification/reduction

Independent directional pattern in each band (N=20, Phonak VoiceZoom)

SNR Improvement

Adaptive System: The noise source with the largest energy

is reduced

CI-SP:Harmony Hearing Aid:

Phonak Exilia

Method: Experimental Design

Methode: Measurement System

OlSA Noise

OlSA Noise

OlSA Noise

60 dB SPL

Speech (OLSA)

Variable Level

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

14

Omni DirMic Noise Reduction DirMic + Noise

Reduction

SRT

in d

B

**

**

**

*

Besser

Results

Average Results:

1970 1980 1990 2000

F0F2

F0F1F2

MPEAK ACE CIS

SAS

HiRes

single channel multi channel

Feature extraction Vocoder

SPEAK

2010

FSP

FS4

HiRes120

CA

SMSP MP3000

Optima

2020

single

channel

CIS+

HDCIS

Summary

Thank you very much!

Sound Coding Strategies for Cochlear-

Implants

Waldo Nogueira Auditory Prosthetic Group, Department of Otolaryngology, Medical University Hannover

Many Slides from Prof. Andreas Büchner and Tobias Rottmann

Slides and Materials available under: http://auditoryprostheticgroup.weebly.com/blog

Contents

• Cochlear Implant Research Interfaces

• VoCoder Sync Modular

• VoCoder Matlab

• DHZ-Simulator

Cochlear Implant Research Interfaces

• Why do we need them?

– Direct Stimulation of the electrodes vs

acoustic processing


• Cochlear

– NIC: API that allows stimulation and recording

for the nucleus implant

• Psychophysics

• Speech Coding

• Matlab/Python interface

– xPC: Real-Time streaming

• Simulink real time interface

– RF generator: Bilateral streaming

- Streaming of pre-defined stimulation sequences

- Possibility of trigger - Capable for bilateral stimulation

• MedEl Research Interface Box (RIB)

User

Matlab

GUI

RIB II Isolation Box

PC


- GUI for implementation of complete psycho-acoustic experiments

- Presentation of acoustic tones also possible - Can be controlled out of matlab via COM

Bionic Ear Data Collection System (BEDCS)

HRstream


• Advanced Bionics

VoCoder

Speech Production Process

Source Filter Model

VoCoder

• Sync-Modular

– http://www.sync-modular.org/

VoCoder

• Matlab Code

The advanced combinational

encoder (ACE)

31.0

8.20

16

Fußzeile 135

The advanced combinational

encoder (ACE)

31.0

8.20

16

Fußzeile 136

Windowing:

Raised Cosine Window - Hanning

31.0

8.20

16

Fußzeile 137

Hamming Window

• This is a raised cosine window function.

otherwise

MnM

n

nw

,0

10,1

2cos15.0

)(

Hamming Window:

otherwise

MnM

n

nw

,0

10,1

2cos46.054.0

)(

Filterbank • FFT is applied to each frame

• Windowed signal is shifted over a time interval equal to the

stimulation period (1/CSR) Ns

• The center frequencies of the FFT bins (fc) are linearly

spaced

• Resolution of the FFT is 125 Hz

• Bin 0 (fc = 0 Hz) and bin 64 (fc = 8000 Hz) are real, bins 1

to 63 are complex

• x(l) real X(n) Hermitian symmetry bins 65 to 127 not

required

• Exercise: Apply FFT on each frame

31.0

8.20

16

Fußzeile 139

Filterbank

• (1) Sampling frequency (fs) of a CI is 16000!

– Resample incoming sound to 16000

• (2) Channel stimulation rate (CSR) is set to

values between 500 and 1500 Block shift

in your analysis should be similar to this.

round(Fs/CSR)

31.0

8.20

16

Fußzeile 140

Envelope Detection (1)

• The linearly-spaced L/2 coefficients obtained

at the output of the FFT are groupped into M

bands

31.0

8.20

16

Fußzeile 141

Envleope (2)

Sampling and Selection

31.0

8.20

16

Fußzeile 143

Mapping • The „Mapping“ block determines the current

level li from the envelope magnitude and the

channel characteristics.

• This is done by using the loudenss growth

function (LGF)

31.0

8.20

16

Fußzeile 144

Mapping (2)

Mapping (3)

31.0

8.20

16

Fußzeile 146

Exercise

• Take the audio signal ASA.WAV

• Plot the electrodogram

31.0

8.20

16

Fußzeile 147

VoCoder: Sound Simulations

31.0

8.20

16

Fußzeile 148

VoCoder

• DEMO: DeHoCI Simulator

Be careful with a VoCoder …

• A VoCoder does not simulate sound

perception with a Cochlear Implant

• However, it is possible to configure a

VoCoder such that similar performance

(e.g. speech) is obtained by Cochlear

Implant listeners and normal hearing

listeners

Documents

Sound Coding Strategies for Cochlear- Implants · 30 years of cochlear implant experience World largest cochlear implant programm (7000 Impl. 2013) 500 patients are implanted every