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FM Transparency Verification

Introduction
The purpose of this Quick Guide is to describe how to verify FM transparency of FM system using the Interacoustics Affinity1 Hearing Aid Analyzer. FM Transparency can be defined as “The condition in which equal inputs to the FM and hearing aid microphones produce equal outputs from the hearing aid.”2 The verification method is according to the AAA Clinical Practice Guidelines for Remote Microphone Hearing Assistance Technologies for Children and Youth Birth to 21 Years. For more information, please refer to the AAA Guidelines.

The FM Transparency consists of 3 easy coupler measurements:

  1. Hearing Aid alone.
  2. Hearing Aid + FM receiver attached, FM transmitter on and muted .
  3. Hearing Aid + FM receiver attached. Transmitter microphone unmuted and positioned inside the test chamber, facing the reference mic. Hearing instrument still attached to the coupler/coupler mic, positioned outside the test chamber.

Verification Steps

  1. Launch the Affinity 2.02 Suite and choose a patient, through Noah or OtoAccess™.
  2. Launch the REM module.
  3. Select the FM Transparency protocol from the drop down menu.

NOTE: FM Transparency assumes that the hearing aid has already been programmed to match the targets, according to the patient’s hearing loss and patient needs. Therefore, there is no need to show targets on the screen. Targets and Fitting prescription information will not appear on the main screen when the FM transparency is chosen.

The FM Transparency setup guide will pop up when the above protocol is chosen, instructing the HCP on how to setup for FM Transparency verification3:

Step 1: HA Alone

  1. Select the HA Alone test.
  2. Attach the hearing aid to the coupler/coupler microphone.
  3. Position the hearing aid in the test chamber.
  4. Click START to measure the output of the hearing aid (red curve).

Step 2: HA + Receiver

  1. Leaving the hearing aid attached to the coupler, attach the FM receiver to the hearing aid.
  2. Turn on the FM transmitter. Mute it.
  3. Click START to measure the output of the hearing aid (purple curve). 


Note: the two curves should be very similar to each other

Step 3: FM Mic + HA

  1. Remove the hearing aid, still attached to the coupler, from the test box.
  2. Position the FM microphone inside the test box, in front of the reference microphone.
  3. Click START to measure the output of the hearing aid when input is from the FM microphone (green curve).


Note:

  • If a significant difference is already seen between the Green curve and the Red curve, one can presume that there is a problem with the FM microphone.
  • Ensure that the test is conducted in a quiet environment, since the hearing aid is outside the test box and the HA microphones are still active.

Step 4: Calculate the average difference

  1. Click on the table mode icon  to activate Table Mode.
  2. Once in table mode, calculate the difference between 750 Hz, 1000 Hz and 2000 Hz and
  3. Calculate the average.
  4. If the average is 2 dB or less, FM transparency is achieved.
  5. If the average is more than 2 dB, adjust the FM.

Example 1

*Average difference is less than 2 dB, therefore transparency is achieved

Example 2

*Average difference is less than 2 dB, therefore transparency is achieved


1To have access to the dedicated FM Transparency test, Affinity suite 2.4 or higher is needed.
2American Academy of Audiology (2011).
3The FM Transparency test is a coupler test, therefore the protocol will start up in coupler mode by default. Coupler mode is indicated by a hearing instrument attached to a coupler on the main screen.

References
American Academy of Audiology (April 2011). Clinical Practice Guidelines: Remote Microphone Hearing Assistance Technologies for Children and Youth Birth to 21 Years (includes supplement A). 

Fernée, Ben Zalm (2012). FM Verification Made Easy 

December 2013
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