John I have the Oticon aids and my audiologist uses the Oticon formula, not really sure what that means. His comment is he has found that the company formula seems to work best in most cases.
IIRC, the fitting formulas are both the way the sound input is quantified and the way it is amplified. (We see only the table with the amplification for each dB-range and frequency band.)
The NAL standards are statistical results. Basically, the amplifications that give people with a specific audiogram the best understanding of speech are put into a multivariant regression and voilà: there you have your scientifically proven best starting point for an amplification scheme for your hearing loss.
For children the amplification is typically too low, not only are their ears better at handling higher amplicifications, but they also don’t register sounds the way adults do. So DSL was the answer addressing that. Unfortunately, people growing up with DSL never liked NAL and then they made adult DSL.
Next to that the different manufacturers decided that they should tweak the scientific results to get better results with their typical hardware. As you’ve probably noticed a lot of marketing has been put into the sound of different aids: With identical chips, mics and receivers the difference will have to come from somewhere. Phonak has Phonak Digital and Phonak Digital Contrast and I do believe that they give slightly better results in understanding people in crowds. However, they also generate painful sounds when my 2 daughters are being loud. NAL2 has overall a lower amplification than Phonak Digital and - Contast so it’s really more comfortable.
I’ve never met an audiologist who didn’t sound skeptical about the commercial formula’s. The most neutral stance was that whatever happened wasn’t documented, so there was no way to assess its merits.
I remember trying to hear a difference between Phonak Digital and Phonak Digital Contrast with an interested audiologist. She wasn’t really surprized nothing came out of it.
Interestingly, Oticon claims a more natural sound nowadays: The bird sounds and everything. That is at least a clear break from NAL2 that is definitely geared towards speech understanding. Whether or not actually achieves it, is in the ear of the beholder, I guess.
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I wear the More1 aids and love the sound. I have worn Oticon aids since 2010 and now when I try other companies’s aids I find the sound to be unnatural. I live out in a forest area of the country and love listening to the birds, bees, and even chipmunks and squirrels make their sounds. I also love just being on a bench on the trails by a stream and listening to the water flowing over a small water falls and listening to the breeze blowing the leaves of the trees. And to top it off my speech understanding is the best it has ever been.
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I use NAL NL2 @John_Green, Like you, I have tried them all… Previously, I always found NAL2, a bit loud for my personal preferences, but about 6 months ago, my NHS A.uD switched me from DSL 5, along with a new set of Naida M70 SP’s, he did REM, for me this was the first time, I have had REM done…… M70’s were loud at first, but after a few weeks, I got used to that initial loudness, it was much clearer and crisper, in fact after about 3 weeks I was so acclimatised to NAL2, using Target, I copied over all the settings in the M70’s, to my privately bought Naida P90 UP 675’s, tis not a perfect match, but near enough, although the improvement is fairly marginal, any improvement is a plus for me…. NHS Audioligist’s are usually by nature, spot on with their programming of aids, they have to be with the sheer volume of clients they see, they only get 1 shot at it, if you want a follow up visit for tweaking, you might wait many months…. He said to me prior to fitting, “I promise you, you will leave here today, hearing much better than you came in” or words to that effect, I thought, maybe so, I have heard that all before…. He was 100% correct, and no further tweaking required…. Cheers Kev 
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People who grow up with DSL child stay with DSL child. There’s no reason to switch them to DSL adult (and the reduction in audibility would be detrimental). DSL adult is a set of prescriptive adult targets on par with NAL, developed out of Canada instead of out of Australia. They started from slightly different ideologies, but with adjustments over time have come to be quite similar. Depending on your hearing loss, NAL-NL2 tends to be a bit more compressed, DSL 5.0 tends to emphasize high frequencies a bit more. Research at this point suggests that they are pretty comparable, with maybe a minor benefit to DSL that could just be an artifact of limited research.
Phonak Digital Contrast was developed for users with severe/profound hearing loss and uses slow compression. Anecdotally, I’ve seen benefit for users with poor clarity, but I still fit it to DSL or NAL targets.
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I could have written your post. The world is back in full colour. VAC+ with REM More 1 (they used the integration in Genie).
I can hear and understand (even the TV) but as I move through the day I also know where the lark is overhead, when the dog wanders into the room, the creaky step I had forgotten about. I second the sounds of the woods and water. Magical. My walks in nature are just so much more food for the soul again with the sense that I can hear and therefore spot and watch just about everything.
I’ve also been surprised by the clarity of more distant speech. I can understand my walking companions much further away and people in other queues in shops 20ft away. Makes me smile.
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I asked here once before and apparently Oticon (if memory serves) allows you to select a different formula per program. I’m not sure which models that applies to, but I think it would be really interesting to compare.
Genie 2 allows that. You select a slot and choose General and then right arrow to select rationale.
So you can for instance have 3 program slots set to General. One for VAC+, one for NAL and one for DSL if you want to. Works for Opn, Opn S and More at least. Not sure about others.
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Very interesting comments. Thanks! I will most likely leave the fitting formula as is. I don’t really detect much difference, if any. Since my high frequency loss is so bad, perhaps the Phonak formula is best for me. There are certain sounds that are very annoying when I am wearing aids. When I mentioned this to a previous VA Audiologist, she just said to grin and bear it. My aids were set properly. I have previously fiddled with the programming to try to help this, and found nothing that actually helped. I have an app for my phone called “Spectroid” that is an audio spectrum analyzer. I used it to see what frequencies those annoying sounds were producing the most, but results didn’t really point to any particular frequency as being the culprit. I thought that since I use “Sound Recover”, those annoying sounds might be previously unheard frequencies being lowered into audible range. But turning “Sound Recover” off didn’t really help much. Speaking of “Sound Recover”, in theory it helps my hearing. I can hear frequencies as high as 10 KHz. But, in real life, all those high frequencies just get translated into lower frequencies that end up being just more noise to deal with. I have gotten used to the sibilance and lisping I get with voices.
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Thank you for these comments and perceptions…they certainly have helped my understanding of the rationale of NAL-NL2.
So as a result, I have gone back to NAL-NL2 from the DSLv5 to see if I get any improvement with my Oticon More1’s.
Thanks also to @John_Green, @kevels55 and all you other commentators for hosting and posting to the thread. 
I’ll get back with comments if I find any significant changes in a week of two.
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The different fitting formulas generally differ from each other mainly in the high frequency areas based on my personal experience of trying them out myself. The DSL Adult and NAL-NL1 and 2 seem to have a sharper edge (hence stronger high frequency sounds) compared to my Oticon VAC+ rationales.
So if you have severe high frequency loss, unless you’re able to make use of the frequency lowering technology effectively, you’re probably not going to be able to discern much differences between the various fitting rationales, because their differences are already considered “just more noise to deal with” as you said above in the bold text.
If you don’t find yourself successful with the Phonak Sound Recover 2 frequency lowering technology, you can try experimenting with other frequency lowering technologies from other brands of hearing aids to see if any of those agree with you more or not. That’s because not all frequency lowering technologies are the same. They run the gamut from frequency compression to frequency transposition to frequency composition to a variety of combinations of these 3 schemes anywhere in between.
But overall, with your severe high frequency loss, you’ll almost certainly need to have frequency lowering, and the right frequency lowering technology that works for you, in order to help you understand high frequency sounds better as opposed to dismissing them as just more noise for you.
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It does. I once had a program for each of the 4 formulas in my Oticon OPN. Having tried them all, I prefer Oticon VAC+ now.
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“Voice Aligned Compression (VAC+) is our proprietary fitting rationale. It is based on time-tested research by our Eriksholm Research Center originating back in the 1990’s. Its goal is to place the amplified moderate speech signal within the most comfortable range, and then set the compression ratios to get the majority of the full dynamic range of speech within our estimate of the patient’s dynamic range.”
I assume by “range” they mean loudness/volume/amplitude, rather than pitch shifting? Anyone know?
I also found this great thread. Sorry I missed it first time around.
There shouldn’t be any pitch shifting in a fitting rationale. Usually pitch shifting is only done in frequency lowering technologies. But that’s separate from fitting rationales.
I think the range they’re talking about here is the region of sound pressure level where the impaired hearing can still hear. Below is a screenshot of an example of Wide Dynamic Range Compression that depicts an example of what an impaired hearing range may look like across frequencies compared to a normal hearing range.
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FWIW
Sorry to resurrect an old thread…but…
As a cynic, I have always been wary of HA manufacturers’ fitting formulas as I believed them to be strongly oriented to comfort and acceptance and therefore increased sales of hearing aids rather than aligned to best speech comprehension.
But, as a result of a recent discussion of fitting formulas on the forum (can’t remember which thread), I finally gave Oticon’s fit formula a real go. I would like to say that I found it very comfortable and I “feel” that it is giving me greater comprehension of speech than any of the other available formulas.
I am struggling to understand the reasons as the Oticon formula damps down some of the high frequency that my audiogram indicates I am really missing. But, who can argue with what appears to be working?
After all these years of trial and error…who would have thought?
Once again, thank you to all and especially to the poster (@Volusiano?) who triggered me to try the manufacturer’s formula.
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I am very glad you did !
self programing P90’s
It has made me look at several different formulas, after trying them all, at the moment I have settled on DHL Pediric … finally, I can HEAR ! The world has come to life.
DSL Pediatric? I think you typoed an H instead of an S.
I think you are correct . 
An excellent resurrection of an old thread, thanks to all contributors.
Should be a sticky!