Frye FONIX FP40D - Manual (Page 158)

FONIX FP40 Portable Hearing Aid Analyzer 150
channel instrument can meet those targets. If the compression ratio targets are very different
in different frequency regions, a dual-channel or multi-channel instrument may provide a bet-
ter fitting for the client. When setting the aid, the compression ratio should be set to match the
average of the target compression ratios in each frequency band.
Warning: If the prescribed compression ratio is greater than 4:1, a WDRC fitting may not be
appropriate for this hearing loss.
In the DSL approach, all measurements are referenced to Sound Pressure Level. HL (Hearing
Level) thresholds, no matter how they are obtained, are changed to real-ear SPL. Once the
threshold is entered, the next step can be to go to the SPL display in the Probe screen to show
the client or parent where the thresholds are in relation to the normal speech spectrum. The
LTASS—Long Term Average Speech Spectrum—will be either the adult’s or child’s, depend-
ing on the age selected. The child’s LTASS is based on Cornekussem, Gagné & Seewald.*
Alternately, the operator can go from the target screen to the target coupler gain screen The
hearing aid prescription curve will be displayed there. It is in this screen that a custom RECD
(Real Ear to Coupler Difference) measurement can be made, using an insert earphone to add
to the validity of the prescription. The hearing aid is now measured in the chamber at a range
of amplitudes. The operator can make adjustments and the aid can be re-tested in the chamber.
Finally, when possible, the operator can return to the SPL screen in the Probe Option and vali-
date the fitting in the real ear. The mid-range target will be displayed on that screen.
*Cornelisse LE, Gagné JP & Seewald RC (1991) Ear level recordings of the long-term average spectrum of speech, Ear
& Hearing, 12(1): 47-54