Do digital hearing aid users benefit from using an fm system in class?

1
Do digital hearing aid users benefit from using
an fm system in class?

• YES !

Wave 4 SFR 17/05/04
2
fm Advantage new procedures

• Digital or analogue ?
• Whether the hearing aid is digital or analogue is
  not important, the relevant factor is whether the
  hearing aid is operating in linear or non linear
  mode

3
fmAdvantage

• Motivated by the wish to ensure better
  fmAdvantage in classrooms
• Motivated by the wish to maximise the benefits of
  fm use by utilising the way the DSP hearing aids
  work to obtain a beneficial s/n ratio
• Lets consider WDRC aids
• Wide Dynamic Range Compression

4
Traditional equal output balancing approach
(65/75)
Linear hearing aid Combined mode
FM advantage lost
Childs ear
Teachers voice
Child and classroom voices
110dB SPL
75dB SPL
65dB SPL
105dB SPL
60dB SPL
Can the child hear the teacher clearly?
Teacher
Classroom noise
Child
5
Design of DSP hearing aids
FM signal enters before any DSP, in parallel with
the microphone input
The loudest input will drive the compressor
6
FM advantage approach (65/65)
Non- Linear hearing aid Combined mode
FM advantage preserved
Childs ear
Teachers voice
Child and classroom voices
Teacher
Classroom noise
Child
7
How do you currently balance an FM System?
8
Non linear test levels

• 65dB SPL for the hearing aid
• 65dB SPL for the fm radio system
• 80dB SPL the reality part of the test, will we
  get an fm advantage?

9
General assumptions

• The hearing aid(s) have been separately assessed
  as working normally
• The hearing aid(s) are recognised as being
  correctly fitted for the user
• The fm Advantage setting up procedures are
  carried out with the hearing aid left at the
  normal user settings

10
Before you start

• Understand the different programmes and ask which
  hearing aid programme is intended for fm use?
• Listen to the whole system (FM hearing aid)
  before you carry out the fm advantage procedures
• Set the test box is to display output
• Use a lapel microphone for the procedure

11
Issues

• Comparison with ASHA 2000 guidelines
• (were more in line but not identical)
• Distortion
• Listen to the system measuring it just produces
  artefacts
• Noise reduction feature
• Not a problem with a DSP stimulus, but you can
  still do the procedure with a pure tone sweep or
  composite signal wait for the FRC to settle
• Interference from DSP hearing aids
• MLx use

12
MLx use

• It may sometimes be the case that transparency
  with MLx and the HA may not be achieved.
  However, it is more likely to be achieved with a
  Phonak transmitter (eg. Campus-S or HandiMic).
• The FM advantage with MLx will vary between
  hearing aids (as it will with conventional fm
  systems), and each aid to be used with MLx should
  therefore be individually assessed before
  fitting.

13
MLx use cont

• Some DSP aids will only work in FMM mode,
  regardless of how the switch is set on the MLx.
  There is quite often a better performance (
  approx 5dB) on the FMM setting.

14
MLx-S

• Programmable version of MLx
• Programming requires PC, Hi-Pro and Toaster
• Presently will be programmed at factory on
  instruction
• Designed for use with Wall Pilot
• Swivelling Pins

15
Lexis

• Collaboration by Oticon, Starkey Bernafon and
  Phonic Ear
• Trim pot on the side of receiver which allows
  adjustment of the response
• 14 dB range
• Fixed channels
• Swivelling pins

16
Interference

• Ref BAEA website/newsletter
• DSP Hearing aids, personal FM systems and
  interference is there a problem? G. Pont
• Also submitted to Ear Hearing
• Summary As with some CI processors, DSP hearing
  aids can cause interference to personal fm
  systems. On the present NHS contract, some aids
  are clean others have quite high levels of
  interference. We are in dialogue with NHS
  supplies manufacturers on this issue.

17
Practical Session

• Listen to FM system with aid of choice (WDRC)
• Follow FM Advantage procedure (see booklet, page
  5) using Genie and FP35
• Choice of MLx, MLx-S or Lexis
• Listen to system
• Check for transparency