RECD Basics and Usage in AudioScan fitting systems

The RECD or real ear to coupler difference is a measurement across frequencies of the output of a sound transducer in the fixed volume of a coupler subtracted from the output of the same transducer in the unknown volume of the closed ear canal.  Since the SPL produced in a closed space varies with volume of impedance, the recd can be used as a characterization of the acoustics of the measured ear canal. the measured RECD can then be used for two purposes.
  1. To correct and convert HL thresholds to the SPL format used by many fitting methods and real ear approaches.
    1. audiometers are calibrated to an average adult ear canal, any differences in volume and impedance will be reflected in the measured hearing levels. using a measured RECD ensures the SPL thresholds accurately capture the true level of hearing sensitivity for the patient in question.
  2. ​To allow hearing instrument fitting in the test box. The RECD is applied to the coupler microphone measurement so that hearing instrument performance in the coupler can be predictive of performance in the real ear.

Step by Step
  • RECD starts with a calibration of the transducer in the coupler; stored weekly
  • Green calibration curve is acquired and stored
  • Uses 0.4 cc wideband coupler and TRIC ​
  • Otoscopy used to check ear canal for obstructions and ensure correct probe tube placement
  • position the probe tube so it is within 5mm of the tympanic membrane
  • connect a foam ear-tip to the RECD transducer and without moving the probe tube, carefully insert to the standard depth and ensure enough time passes for the foam to fully expand
  • The personal ear mold can be substituted for the foam ear tip in the real ear measurement to capture the tubing characteristics and subsequent applications of the measured RECD.
    • ​Note that in the audiometry window there is a selection for the transducer used in the HL measurement and a separate one for the coupling type used in the RECD measurement. It is important to specify when using an earmold for RECD. However, for ear molds where the total tubing length is less than 35mm, we recommend that you select foam ear tip so a more appropriate correction is applied
    • when using an earmold for the RECD measurement, be sure to block vents at the medial end, lubrication can be used
  • Select measure Real Ear
  • On screen the measurement will be shown as a magenta curve
  • When that stabilizes it is captured and stored and the RECD will be generated as a blue curve
  • The dotted line represents an average age-specific RECD
  • Since the volume of a 2cc coupler is much greater than that of an ear canal, the SPL in the coupler will be much lower than that measured in the ear and the resulting RECD value always positive.
  • A negative RECD in the low frequencies will normally indicate a poor seal during the on ear measurement, it should be noted that this can also result from a perforation of the TM or a PE tube in place.
  • If the RECD curve is more than 10dB different from the average it is suggested that you check for probe tube placement issues or blockage and remeasure.
  • An average RECD value will have values below zero and negative numbers are not unexpected, however, a leak in the on ear measurement will still result in a steep rolloff in the low frequencies.

REM Intructions for the Verifit Step by Step

Use the Verifit Help Menu for further explanation of any step below 
  1. Open up Audiogram profile in software
  2. Open Audioscan
  3. Transfer audiogram to Verifit
    1. Verify received data verification from NOAH module
    2. Select the green checkmark to continue
  4. BE SURE TO MUTE THE HEARING AIDS WITH AN OPEN DOME!
  5. Cycle through the measurements prompting the patient through each one, don't forget to unmute the hearing aids when testing!
  1. Otoscopy
  2. Select On-ear, Calibration
    1. Put a probe tube on the probe mic assembly
    2. Hold the left and the right 3-6 inches in front of the speaker and click calibrate one at a time
  3. Select On-ear, Speechmap
    1. Warning Max TM SPL safety limit disabled
    2. Click the check box
      1. Max TM saftey sets the limit at which the Verifit will automatically discontinue testing if the SPL at the TM reaches the set limit
  4. Select the type of HA from the dropdown menu
  5. Complete the information under the Audiometry tab.
    1. Targets
    2. Age
    3. HL transducer
    4. Bone Conduction
    5. UCL
    6. RECD
    7. Binaural
  6. Enter the thresholds
  7. Test REM
    1. insert the probe into the ear canal getting as close as possible to the TM
    2. Make sure the probe mic is facing away from the patients neck and Forward toward the speaker
    3. click on the green arrown in each of the testing conditions to start the testing
    4. let the carrot story run all the way through once and then hit the record button
    5. complete all 4 test scenarios
      1. Average Speech
      2. Soft Speech
      3. Loud Speech
      4. MPO​​
  8.  Make sure you hold/stabilize the probe tube in place, Make sure you perform otoscopy, Make sure you have entered all of the correct information regarding the hearing aid and the fitting (everything under the "Audiometry" tab)

RECD Instructions for Verifit Step by Step

  1. Select WRECD from On-ear Verifit Menu
  2. Click the green checkmark for the MAX TM SPL safety limit Warning
  3. Select the on-ear coupling method (Foam Tip or Mold), click the green checkmark
  4. Select Calibrate WRECD transducer
    1. ​Plug the WRECD transducer into the jack labeled RECD on the Probe dock (purple microphone jack/purple WRECD)
    2. Attach the TRIC adapter to the 0.4cc coupler (silver fitting) and attach this to the blue coupler microphone.
    3. ​Insert the nozzle of the WRECD transducer all the way into the opening of the TRIC
    4. Select the green checkmark
  5. When the green curve stabilizes, click the green checkmark
  6. Select RECD coupling method (foam or mold)
  7. Select Measure Real Ear
    1. ​Couple a standard insert earphone faom eartip to the nozzle of the WRECD transducer
    2. Position the probe tube in the ear canal as for a REAR measurement
    3. Insert the foam eartip into the ear canal as for a threshold measurement, being careful not to move the probe tube
    4. Select the green checkmark
  8. ​Select the green checkmark when the curve stabilizes
  9. Next step is Speechmap

Probe Tube Placement