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An Update on Hearing Aid Testing. Reading Speech-Maps or SPLograms Niki Timar, Audiologist Vancouver Island Health Authority – South Island. Background . Audiologists used to routinely test hearing aids in the booth, using aided audiograms. Background.

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an update on hearing aid testing

An Update on Hearing Aid Testing

Reading Speech-Maps or SPLograms

Niki Timar, Audiologist

Vancouver Island Health Authority – South Island

background
Background
  • Audiologists used to routinely test hearing aids in the booth, using aided audiograms
background1
Background
  • Research has shown aided audiograms are not a good way to test modern hearing aids
  • BC Public Health is switching over to the newer way of testing, using Real-Ear or simulated Real-Ear measures
  • This is why you might not be receiving aided audiograms recently
what is a speechmap or splogram
What is a SpeechMap or SPLogram?
  • A graph showing hearing thresholds, maximum safe or acceptable levels, and the performance of the hearing aid
  • “Speechmap” is the proprietary term Audioscan uses for their software
  • “SPLogram” is a term coined by Richard Seewald and his group, from the University of Western Ontario, for use with the Desired Sensation Level (DSL) hearing aid prescription formula
slide6
Audiogram on Speechmap Screen

In dB Hearing Level (HL)

Normal Hearing

“Speech Banana”

Hearing Thresholds

slide7
Speechmap or SPL-o-gram

In dB Sound Pressure Level (SPL)

Hearing Thresholds

“Speech Banana”

Normal Hearing

slide8
Difference Between Speechmap and Audiogram

Loud

In dB

Sound Pressure Level

NOT Hearing Level

Soft

slide9
Too Loud

Aided “Speech Banana”

Inaudible

why not aided audiograms
Why Not Aided Audiograms?
  • Aided audiograms only show one thing: the response of the hearing aid to very soft sounds
  • Aided audiograms do not tell anything about how loud the hearing aid is, and whether it is potentially damaging to a child’s hearing
real ear testing
Real-Ear Testing
  • Instead of Aided testing in the booth, we now rely on Real-Ear Testing as our main hearing aid test
what is real ear testing
What is Real-Ear Testing?
  • Real-Ear testing is objective testing with the hearing aid in the ear.
  • Basically, we place a microphone in the ear just past the hearing aid, and measure what the actual output of the hearing aid is, close to the eardrum
why the changes in methodology

Why the Changes in Methodology?

A Short Lesson on Hearing Aid Technology

hearing aids
Hearing Aids
  • Hearing aids are now digital
  • Hearing Aids are no longer linear, they use COMPRESSION
dynamic range
Dynamic Range
  • One important concept for understanding compression and hearing aid function is DYNAMIC RANGE
  • This is the range of usable hearing for a given individual – between the quietest sounds they can hear (hearing thresholds) and the loudest sounds they can tolerate (loudness discomfort levels)
slide18
HL

Hearing Thresholds

Dynamic Range

Maximum Output

slide19
SPL

Maximum Output

Dynamic Range

Hearing Thresholds

linear hearing aids
Linear Hearing Aids
  • Until the 1980’s, hearing aids were linear
  • They added the same amount of amplification, no matter how loud the input sound
linear amplification
Linear Amplification
  • 140
  • 120
  • 100
  • 80
  • 60
  • 40
  • 20
peak clipping
Peak Clipping
  • 140 dB is dangerously loud for most people
  • To keep the sound levels safe, hearing aids used Peak Clipping – they just stopped at a given level – for example, they wouldn’t make anything louder than 120 dB
  • This caused DISTORTION in the hearing aids
peak clipping1
Peak Clipping
  • 140
  • 120
  • 100
  • 80
  • 60
  • 40
  • 20
compression
Compression
  • In the 1980s, as a way to keep sounds comfortable but undistorted, manufacturers started using compression limiting
  • Instead of amplifying the same amount no matter what the input, for sounds approaching the limit, less amplification would be used
compression1
Compression
  • 140
  • 120
  • 100
  • 80
  • 60
  • 40
  • 20
even newer advances
Even Newer Advances
  • As technology advanced, it became possible to have different compression levels for different frequency ranges, and for different intensities
  • This is where digital hearing aids shine, as more capability can be added in these functions, without adding size or battery drain
so what does this have to do with speechmap
So What Does This Have to Do With Speechmap?
  • Testing just quiet sounds in the booth does not tell us about what the hearing aid does to speech
  • Digital hearing aids often have noise suppression, which makes quiet, non-speech-like sounds even quieter, to avoid amplifying annoying sounds like fridges humming
  • Aided audiograms are tested using quiet, non-speech-like sounds (tones)
limitation of aided audiogram
Limitation of Aided Audiogram
  • This slide shows the hearing aid’s response to quiet non-speech tones
  • We can infer how much speech the child can hear, but it does not show differing performance for soft, versus loud, speech
  • It does not tell us if the hearing aid is too loud, or if there is distortion
  • There are no targets, so we don’t know if this is a “good” fitting
slide31
The Speechmap shows soft speech, loud speech and very loud sounds, showing, in this case, that they all give acceptable responses
  • It also shows Speech Intelligibility Index (SII), which predicts how much of the speech signal is audible for a given input
slide34
The Speechmap shows clearly the limitations of what can be achieved with hearing aids for difficult fittings
  • This keeps us from trying to increase the volume where it does not help, and would only cause feedback problems
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