The Real Ear to Coupler Difference (RECD) is a measurement that accounts for the decibel difference across frequencies between SPL measured in the coupler and the SPL measure in the real ear, produced by the same transducer generating the same signal. This ensures that information about the patient’s occluded ear canal characteristics is obtained.
Due to the physically smaller size of the ear canals for infants and children compared to adults, and because it would be very difficult to do real-ear verification on them, the RECD is an important measurement in the pediatric hearing aid fitting process. It enables clinicians to verify the frequency/gain characteristics of the child’s hearing aid while it is attached to the 2cc BTE coupler, without the need to have the child’s ear physically present. Since children have physically smaller ears than adults, and smaller ears equals higher SPL, not taking the RECD into account would likely lead to over-amplification. For more information on RECD and the recommended guidelines for pediatric hearing aid fittings, please refer to the references at the end of this document.
Measuring the RECD
There are two ways of measuring the RECD: with the patient’s ear mould or with the SPL60 RECD probe tip.
Measuring with ear moulds will be a bit more precise than measuring with the SPL probe, however; in situations where a quick measurement is needed, using the SPL probe will be much quicker than measuring with the ear mould. In situations where no measurement can be obtained, it is recommended to use age appropriate, predicted RECD values. Instructions for all three methods are detailed below.
RECD measurement with earmold
RECD Measurement with SPL60 Probe
Using age appropriate predicted RECD values
If it is impossible to get an RECD measurement (ex: child is crying or uncooperative), it is recommended to use age appropriate predicted RECDs.
Own Mould versus SPL Probe
Whether the RECD is performed using the client’s own ear mould or the SPL probe may have an effect on the result. The benefit of using the client’s own ear mould is that the measurement will reflect your client’s actual residual volume whereas the SPL probe only provides an estimate. However, you may be in a situation where the ear mould is nonexistent, broken, or has an extremely bad fit. Furthermore, you might need to conduct measurements on children not willing to co-operate. In these situations the SPL probe offers the benefit of easy probe placement and measurement.
Below, see two RECD measured in the same ear using the SPL probe and own ear mould respectively. Note: the differences between the two ways of measuring. As can be seen above the curve measured with the client’s own ear mould is below 0 in the low frequencies. This may be due to ear mould effects such as the tightness of the fit and venting and in the insertion depth of the SPL probe or ear mould.
Using the RECD in the hearing aid fitting
The RECD can now be used for the hearing aid fitting. The RECD can be imported, if that feature is supported, manually into the hearing aid software. The fitting will be recalculated while taking the RECD into account3. To view the RECD values, click on Table View.
To proceed with the hearing aid verification, click on the REAR button; the software will automatically go into the coupler mode and it will then be possible to proceed with the verification. The default fitting formula will be DSL v5 Pediatrics. Use the hearing aid software to fine tune the hearing aid and to ensure that the output is matching the DSL targets for soft, average, and loud, using a speech stimuli (like the ISTS). Measure the MPO to ensure that the output for loud sounds is not hitting the UCL.
Visible Speech Mapping can also be used for coupler based fittings. This can be done by choosing the Visible Speech Mapping in the REM module, rather than the REM440 module it self. Note that Visible Speech Mapping requires a separate license.
1Not all hearing aid manufacturers support RECD imports. Contact the hearing aid manufacturers if unsure.
2If always using the SPL probe rather than ear moulds, it is possible to create a protocol to ensure that the “Use the insitu SPL probe” option is always ticked off. For information on how to create protocols, please refer to the Instructions for Use or Additional Info manuals for Affinity 2.0 or Callisto™.
3Not all hearing aid manufacturers’ software support the import of RECDs. If unsure, check with the hearing aid manufacturer.
Bagatto MP. Optimizing your RECD measurements.The Hearing Journal 2001; 54: 32, 34-36.
Bagatto MP. The Essentials of Fitting Hearing Aids to Babies. Seminars in Hearing 2013; 34:1, 19-26
Bagatto MP (2007). Learning the Art to Apply the Science: Common Questions Related to Pediatric Hearing Instrument Fitting.
McCreery, Ryan. RECD is a Reasonable Alternative to Real-Ear Verification. The Hearing Journal 2013; 66:7, 13-14. Munro, Kevin. Integrating the RECD into the Hearing Instrument Fitting Process.
Purdy, J and Sheila, T. (2008). Measuring RECD on a Young Child.