Presentation on theme: "Do digital hearing aid users benefit from using an fm system in class? YES ! Wave 4 SFR 17/05/04."— Presentation transcript:
Do digital hearing aid users benefit from using an fm system in class? YES ! Wave 4 SFR 17/05/04
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
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
Linear hearing aid Combined mode Teacher’s voice Child and classroom voices Child’s ear Teacher Classroom noise Child FM advantage lost Traditional equal output balancing approach (65/75) 75dB SPL 60dB SPL 65dB SPL105dB SPL 110dB SPL Can the child hear the teacher clearly?
FM signal enters before any DSP, in parallel with the microphone input The loudest input will drive the compressor Design of DSP hearing aids H.A. MIC F.M. INPUT A/DDSPD/AREC. >> > INPUT
Non- Linear hearing aid Combined mode Teacher’s voice Child and classroom voices Child’s ear Teacher Classroom noise Child FM advantage preserved FM advantage approach (65/65)
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?
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
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
Issues Comparison with ASHA 2000 guidelines (we’re 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
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.
MLx use cont… Some DSP aids will only work in FM+M mode, regardless of how the switch is set on the MLx. There is quite often a better performance ( approx 5dB) on the FM+M setting.
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
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
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.
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