Facts or myths about frequency lowering in hearing

aids

Michael Nilsson, Ph.D.

Head, Audiological Training and Education

1/6/2017 2

Who is Michael Nilsson?

26 years in hearing research and hearing device industry

Accomplishment

• Worked at four manufacturers, clinical

practice, university, research

• Adjunct faculty University of Utah,

Central Michigan University

Accomplishment

• Lead author of the Hearing In Noise

Test

• Co-author of two signal processing

patents

• Lectured on four continents

Degree

• BS, Cognitive Science…

• MS, Social Science

• PhD, Psychology

1/6/2017 3

Agenda

Fact or myth: Frequency lowering is a recent invention

Fact or myth: Frequency lowering can be accomplished by more than one

method

Fact or myth: Frequency lowering degrades sound quality

Fact or myth: Frequency compression contributes to sound deprivation

Fact or myth: Extended bandwidth devices remove the need for frequency

lowering

Fact or myth: Frequency lowering leads to dependence

1

2

3

4

5

6

1

Frequency lowering is a recent invention

1/6/2017 4

Fact or myth

1/6/2017 5

A history of frequency lowering

When did frequency lowering first get patented for the treatment of hearing

loss?

First patent: 1925 in the UK

When was the first commercially available product with frequency lowering?

First commercial product: 1972 Oticon TP72

When was the first commercially available digital product with frequency

lowering?

First digital commercial product: 2000 HD11 by RION

1

Frequency lowering is a recent invention

1/6/2017 6

Fact or myth

2

Frequency lowering can be

accomplished by more than one method

1/6/2017 7

Fact or myth

1/6/2017 8

Kneepoint

Compression ratio

Frequency

transposition

Frequency

compression

1/6/2017 9

Frequency lowering Marketing names

2

Frequency lowering can be

accomplished by more than one method (or a hybrid of both)

1/6/2017 10

Fact or myth

3

Frequency lowering degrades sound

quality

1/6/2017 11

Fact or myth

1/6/2017 12

Perceptual dimensions relevant to Frequency Lowering

FrL default

FrL stronger

FrL weaker

Familiarity of low

and mid frequency

sounds

like \A\, \E\, \I\

Access of high

frequency

sounds

like \S\, \F\, \TH\

Familiarity of

high frequency

sounds

like \S\ & \SH\

1/6/2017 13

A trade off

Audible artifacts are more likely with more aggressive frequency

lowering

• Frequency transposition is more likely to generate artifacts than

compression because sounds are summed

• Creates dissonant sounds or side tones

More aggressive frequency lowering is meant for more severe losses

• The trade-off is between a less natural sound or not hearing

3

Frequency lowering degrades sound

quality

1/6/2017 14

Fact or myth

4

Frequency compression contributes to

auditory deprivation

1/6/2017 15

Fact or myth

1/6/2017 16

When are sounds audible?

Both fall below threshold

above 2000 Hz (speech

peaks are audible to about

2500 Hz – not shown)

Hearing Aids A and B are

both modern devices, and

are at maximum settings in

this region A severe sloping loss Hearing aid responses

and targets for speech

(input at 65 dB SPL)

1/6/2017 17

1/6/2017 18

With a high frequency hearing loss… Deprivation at the cortex will occur

High Frequency information

cannot be processed

Information cannot be resolved due

to damaged regions of the cochlea

Information can be processed

Information can be resolved when

presented where hearing is still

possible

With Frequency lowering, more information gets to the cortex, just at

different frequencies… Deprivation at the highest frequencies will not be

changed

1/6/2017 19

1/6/2017 20

Frequency lowering spectrograms

Original Signal Frequency lowering

High frequency HL

1/6/2017 21

Fitting recommendations

• Use a plurals test or logatome Test to determine whether high frequencies are

detectable

• If not, apply default frequency lowering

• Test for discrimination by comparing ‘s’ versus ‘sh’

• Increase frequency lowering as necessary for access and use of high frequency

content

• Adjust as necessary for sound quality while acclimatization occurs

4

Frequency compression contributes to

auditory deprivation

1/6/2017 22

Fact or myth

5

Extended bandwidth devices remove the

need for frequency lowering

1/6/2017 23

Fact or myth

1/6/2017 24

1/6/2017 25

1 10 2 3 4 5 6 8

Frequency (kHz)

<<S>>

<<S>>

<<SH>>

<<SH>>

1/6/2017 26

Broadband response?

1/6/2017 27

Broadband response?

1/6/2017 28

Broadband response?

1/6/2017 29

Broadband response?

1/6/2017 30

Target Groups where Frequency lowering can be

implemented

Severe to Profound

• Audibility is the greatest gain

• Awareness is the biggest target

• Frequency lowering has the biggest potential to provide audibility with no

side effects if it doesn’t help

Mild to Moderate

• Extended bandwidth is often preferred, but distortion in damaged ear is

possible

– Not useful If high frequencies don’t sound tonal, or sound is harsh and

uncomfortable

• Target High Frequencies that are hard to reach with conventional

amplification

5

Extended bandwidth devices remove the

need for frequency lowering

1/6/2017 31

Fact or myth

1/6/2017 32

Frequency lowering leads to

dependence

6 Fact or myth

1/6/2017 33

The flexible auditory system

The auditory system is very flexible and adaptive

• We understand a wide range of voices

• People can communicate with even severe losses

It works very hard to compensate for any difficulty

1/6/2017 34

Speech variation in speech

‘The quick brown fox

jumped over the lazy dog’

• Two green lines mark 1500

and 4000hz

• The auditory system copes

with 1 octave variation all

the time without it sounding

unnatural

1/6/2017 35

With any change, the auditory system must learn to listen

again

Less information = dependence

More information = benefit

1/6/2017 36

Frequency lowering leads to

dependence (just like dependence on amplification)

6 Fact or myth

The need for acclimatization

1/6/2017 37

Use Frequency lowering when it adds audibility and clarity

• Variability across 1 octave is not a problem

• Will need some time to adjust

• Added audibility should eventually give listeners information

they can use to improve hearing

Shifts from 8 kHz to 3 kHz is >1 octave

1/6/2017 38

Agenda

Fact or myth: Frequency lowering is a recent invention

Fact or myth: Frequency lowering can be accomplished by more than one

method

Fact or myth: Frequency lowering degrades sound quality

Fact or myth: Frequency compression contributes to sound deprivation

Fact or myth: Extended bandwidth devices remove the need for frequency

lowering

Fact or myth: Frequency lowering leads to dependence

1

2

3

4

5

6

michael.nilsson@phonak.com

Together,

we change lives