It’s apparent that the Phonak APD puts emphasis on more gain between the 1-2 KHz range, then slightly less emphasis with slightly less gain in the 2-4 KHz range, and much less emphasis with much less gain in the 4-8 KHz range, all relative to the DSL adult formula.
Obviously Phonak doesn’t give any justification on why it’s doing that (or maybe they did in the material you saw but you didn’t share it here), so we can only guess. To me, they’re kinda saying that the 90+ dB loss in the 4-8 KHz range is very hard to compensate for and may lead to other issues such as feedback if driven too hard, so they might have given up on amplifying too much in this range because the return on investment is minimal so it’s not worth trying. Frankly, I agree with them because even for speech, there would be very little element of speech components that high up in that range. In a way, they’re saying that that heavy of a loss (around 95 dB loss) in that range is too far gone to recover, so why bother? You’re probably better off using their Sound Recover 2 frequency lowering if you truly want to access sounds in that range. And I would agree with them on this as well.
As for the 2-4 KHz range, they seem to give a fairly equal weight to amplification in the 50 dB input (soft sounds), and less weight on amplification for the 65 and 85 dB inputs. If I had to guess, I would say that it’s because they probably think that DSL gives too much emphasis on amplifying on medium and loud sounds in this range, which may result in a harsher tone than necessary than the user wants to tolerate, so maybe they think a less harsh, more comfortable amplification in this range would give a better experience to users. The soft sounds do get a slighly more boost at 2 KHz but slightly less boost at 4 KHz compared to DSL, again to make sure soft sounds are heard better at 2 KHz with APD but it’s not necessary to make it sound too harsh at 4 KHz.
Then at 1-2 KHz, the Phonak APD amplification seems to be much more aggressive than DSL. I think Phonak thinks that this is where a majority of the speech components resides, much more so than those above 2 KHz, so therefore more amplification emphasis here will give more bang for the bucks, so that’s why Phonak would prefer to put amplification emphasis where it’s more effective for speech and everything else.
Personally, I think that the Phonak APD would sound better overall and much less harsh than DSL, because DSL puts too much emphasis on the very high frequencies end, where Phonak prefers to put more amplification emphasis on where the majority of the sound components reside, below 2 KHz.
With this kind of very steep ski slope loss presented here, I think the Phonak APD strategy makes more sense, because more than likely, this kind of loss should be coupled with the use of the Sound Recover 2 frequency lowering technology anyway, so it’s not like you’ll lose all the high frequencies sounds if you’re going to recover them in the lower end with Sound Recover 2 anyway.
That’s my 2 cents of guessing.
