Audioscan Verifit can be used to objectively determine frequency lowering candidacy and properly adjust frequency lowering settings to restore audibility for important speech cues with minimal interference with the existing aided bandwidth. The frequency lowering clinical procedure begins first by completing a conventional Speechmap verification fitting. Once the fitting is completed, you get Real Ear Aided Response result obtained in the presence of a 65 dB SPL average speech passage (ISTS signal).
Next, if you’re going to activate frequency lowering, then you must first identify the maximum audible output frequency (MAOF) range. The MAOF range is the range of frequencies that can be identified using as your starting point the previously measured 65 dB SPL REAR average speech banana.
Since I don’t have an Audioscan Verifit I tried to simulate the output. In this photoshoped image, that include my left ear audiogram, the low-frequency end of the MAOF range is defined as the frequency where the aided long term average speech spectrum (LTASS) for an average speech input (the thick line in the middle of the green shaded area) first crosses back under threshold. The high frequency end of the MAOF range is defined as the frequency where the top line of the green shaded area for an average speech input first crosses back under threshold. The range of frequencies between these two points is the MAOF range.
According to this simulation that is not precise for sure, the low-frequency end of MAOF is at 500 Hz and the high-frequency end is at 1300 Hz. Only two or three frequency lowering systems can lower the high frequencies below 1300 Hz - The Enhanced Audibility Extender by WIdex (lowers down to 650 Hz), Sound Recover 2 by Phonak (down to 800 Hz) and maybe Spectral iQ by Starkey (500 Hz). All high frequency sounds should be lowered and positioned so that the upper shoulder of the lowered hump lands inside of the MAOF range. Ideally, the downward side or upper shoulder of the lowered hump should be positioned as close to the high frequency end of the MAOF range as possible.
What do you guys think about my experiment? Can I get any benefit with frequency lowering or the situation is hopeless with such a severe loss?
This is the simulation with my right ear audiogram. With only 920 Hz high frequency end of MAOF I guess only residual energy of the lowered sounds will be aidable.