We’re getting away a bit from critiquing the YouTuber’s comments on power and venting and related fitting problems but you’re right on DSL5-Adult vs. NAL-NL2. I’ve examined them for my fit vs. the ReSound Audiogram+, which ReSound says is more akin to the original NAL-NL(1). ReSound claims its users actually have a better speech-in-noise experience with Audiogram+ but I’ve briefly tried both NAL-NL2 and DSL5-Adult and think that they both have at least a slight edge over Audiogram+ in speech clarity. They both bring up soft input compared to Audiogram+. But DSL5 really cranks up the high frequencies and shows no mercy on loud input. The thing about NAL-NL2 is it backs off gain for loud input (80 dB). Consequently, it has far more compression than either Audiogram+ or DSL5-Adult. DSL5 is way too loud for me. Running aerated faucet water is very annoying. With NAL-NL2, although soft sounds are a bit more aggressive than Audiogram+, some of the loud sounds are actually more restrained - so it might be a keeper. The price for “best” speech clarity, though, might be a less natural sound environment for average listening than a fitting algorithm that is flatter and more generously spreads relative sound volume out rather than compressing it all down to a more narrow fitting range.
Thanks for the reference. I came across it, too, in preparing to try NAL-NL2 vs. DSL5-adult early this AM. I have seen other material that says that the exact way a HA OEM implements NAL-NL2 or DSL5-Adult can affect the fitting outcome for an individual (forget whether article you reference mentions that consideration). So apparently not all implementations of these generic protocols are created equal.
On how the fitting range is not the be-all, end-all for whether one will have a satisfactory fit for a hearing loss, the following article discusses some other considerations such as fitting algorithm to be used, dome and venting. Fig. 3c shows that a fitting range that was O.K. for a bass dome, single vent is not OK for an open vented dome, etc. Fig. 1 compares fits for OEM’s comfort fit, NAL-NL2, and DSL5-Adult. My own results for MP receivers for Audiogram+, NAL-NL2, and DSL5 are shown in the pictures below, as predicted by ReSound’s Smart Fit 1.4. And a last picture for DSL5 with a Low Power Receiver. The pictures shown that even a Medium Power receiver barely handles the high frequency amplification required for my loss according to DSL5 and a Low Power receiver tops out and the amplification is clipped at the highest frequencies. The inability of the Low Power receiver to handle loud input for the highest frequencies creates, in effect, an artificial unprescribed sound compression (see output table for Medium vs Low Power DSL fits below).
Another useful thing that I learned along the way is that age, sex, binaural vs. a monoaural fit are important to determine the prescribed gains for the various fitting algorithms. I hadn’t been putting age and sex into my fitting software before calculating prescribed fit but from now on I shall be sure to do so (a binaural fit, for example, reduces the prescribed fit for each ear about 3 dB as compared to a monaural fit, if I remember correctly - think it’s for NAL-NL2).
Update_Correction: The binaural fitting difference vs. monoaural out of the paper MDB cites in his post above is: “Bilateral fittings: DSL m[i/o] prescribed targets for speech are reduced by 3 dB across input levels for bilateral fittings re: unilateral fittings (Scollie et al., 2005). NAL-NL2 has a bilateral gain correction that increases with input level. The correction for binaural summation is 2 dB at low input levels and up to 6 dB at high input levels for symmetric losses, and less for asymmetric losses.” End_Correction
source: http://www.sonici.com/Sonic/For-professionals/Downloads/~/media/B8E3BB25ACC949BF9B4B37B06011D917.ashx
In the images below, the black dashed lines are the prescribed output gain for 50, 65, and 80 dB SPL input, the red boxes are the actual output the software predicts the receiver will realize in the “average” ear. So on the right of the DSL5 Low Power Receiver (last image), one can see that this receiver is incapable, by a few dB, of producing the prescribed output at high frequencies and in consequence moderate (65 dB) and loud (80 dB) input at some high frequencies are squashed together and have ~the same volume to the ear. The solid red line at the top of each curve is the Maximum Power Output of the receiver.
Audiogram+(Medium Power Receiver) NAL-NL2(Medium Power Receiver)
DSL5-Adult (Medium Power Receiver ) DSL5-Adult(Low Power Receiver)
(You’re obviously more knowledgeable on the technical end than I am)