Fitting Rationales: VAC+ vs. NAL-NL1, NAL-NL2 or DSL v5.0a

Hearing Aids
#1

I was at my audiologist today to be measured for my Alta2 Pros, and while I was there she entered my audiogram into the Genie software to check out fitting recommendations. She pointed out the different fitting rationales in passing, and I later became curious about the differences between them. As I understand it, VAC+ is Oticon’s default, proprietary fitting rationale, but an audiologist can optionally use the “industry standard” AL-NL1, NAL-NL2 or DSL v5.0a rationales. What are the differences between the four, and why would one choose a particular one over the others?

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Fitting Protocol -Mfg. Proprietary, NAL1, NAL2, DSL, wing it?
#2

Hi,

I´d sure like to know, too.

What I know is roughly the following:

  • the easiest formula would be just to amplify your loss up to 0 db, so you´d (in theory) hear “normal”. Problem: People find this very “unnatural”, background noise drives them crazy
  • based on this: amplify half of your loss or one third of your loss

The actual formulae are much more complicated, they take in account which frequencies are important for speech, what your level of discomfort is and so on.

Nal-nl1 is louder (in most cases) than nal-nl2. DSL is even louder than both nal formulae. The proprietary formulae are, in most cases, softer to give a good first impression.

In my case, for instance, I have the bernafons I´m currently testing fitted with nal-nl2, because the aid I tested before was fitted with nal-nl2, and the proprietary formula seemed too soft for me. But in the meantime I have read a bit about that, see here, section “rationales”:

So I´d like to try out the proprietary “bernafit” formula. No matter what you try, you´ll have to get used to it, first. Then you´ll have to do some testing, it´s almost like testing a completely new hearing aid. I really cannot say “this is best”, you´ll have to try. In your case, it might be a good idea to start with the proprietary rationale, cause you´re a “beginner”.

Best regards,

Musician_72

Oticon Programming Help
#3

seriously guys you want someone to enter that much information because you wont use google?

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#4

Hi,

I don´t think that google will answer the question “which is best for who”. It would be, for instance, interesting, if the acousticians here on the board could tell if they usually use the vendor-formula or something else.

Of course, if you google for vendor formulars, you will find the vendor-sites, saying that their formula is much better than nal - what else should one expect?

No, I don´t think it´s a silly question.

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#5

I agree. I’ve read all the ad copy and I even read a white paper on VAC (couldn’t find VAC+) and it was interesting but didn’t give me any real idea when one would prefer one rationale over another. Of course Oticon thinks VAC is better, but what do people who actually fit hearing aids think?

#6

Generally new users are best at sticking with the manufacturers preferred fitting rationale (usually their own). They devised it with their own circuit and have done hours of testing with it. Where as NL1 and 2 are averages regardless of hearing aid. NL2 replaced NL1 as we found NL1 prescribed too high of gain at high level inputs and too little gain at soft level inputs. In addition to compression ratio’s being prescribed too high for those with severe-to-profound hearing losses. NL2 addresses the issues with NL1. Hearing aids are becoming more complex and “average” will only take you so far, hence manufacturers developing and tweaking prescriptive fitting rationales for THEIR aids. DSL is a pediatric fitting rational. We almost always stick with DSL fitting kids because max audibility is the #1 goal. Occasionally previous users won’t like hearing through a “proprietary” fitting rationale, in which case I will set them back to the rationale they have grown accustom to, most likely NAL-NL2. VAC+ is similar to Widex’s trusound compression strategy that REALLY tries to emphasis soft speech.

#7

Thanks, SteveAUD. That’s good info. My doctor set me up with two programs to start: VAC+ and NL-1 (with the idea of seeing how I liked the flatter response curve). As you said, I definitely preferred the VAC+. At my recent 1-week follow-up I had had her just delete that program, which I had used less than 5% of the time.

#8

Most manufacturers’ proprietary fitting formulas are geared toward initial acceptance. In other words, they usually underfit people so they’re more comfortable and won’t reject the hearing aids. Independently validated approaches such as NAL and DSL are optimized for speech intelligibility and preferred loudness levels. And DSL does have adult targets, so it’s not just for children.

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#9

I take it, then, that you would recommend switching from VAC+ to one of the other formulas despite my initial preference for VAC+? And if so, could you give me an idea of when one would prefer NL-1, NL-2 or DSL?

#10

I think it depends on what your goals are. If you want a very natural and comfortable sound quality, then the proprietary formula will likely work well. But if you want the best audibility of speech, NAL and DSL are both proven approaches. I would suggest that you try a verified (using REM) fitting with NAL-NL2 or DSL v5 and see how you perform on a speech-in-noise test, and then compare it with the proprietary formula.

NAL-NL2 vs SmartFit and Real Ear Measurements
#11

Thanks for the inspiration! This morning I switched Alta Pros to NAL-NL2, Exact. I will try this for a while.

Oh I should say, Exact as opposed to Balanced or Gentle.

#12

You’re stopping the Alta doing what it can by using a fixed formula like NAL. One of the main features of the Alta was the floating point linearity, which dynamically moves linear speech gain at different longer term ambient noise levels.

#13

Without REM, it’s unlikely you’re getting an NL2 fitting. There was a report in Hearing Review last month that showed most manufacturers’ NL2 settings vary considerably from NL2 targets.

#14

I checked with Oticon about this before and they told me Speech Guard is active even if you don’t use their proprietary formula. Also consider that Sensei Pro, their pediatric product, doesn’t contain VAC but still has Speech Guard.

#15

I couldn’t hear any difference. I went back to VAC / Lively. Lively as opposed to Exact, Balanced, Gentle, or Steady.

#16

Which is a good thing IMHO. But it also takes experience to know which manufacturers over do it and go in and make manual adjustments yourself. It’s also why all manufactures utilize some sort of acceptance manager to gradually build peoples tolerances up. I always err on the side of comfort to begin with. I never want people to walk out of my office with their aids on “edge” of being too loud. I’m not trying to give them some huge wow effect from the get go. We wake up in the morning and squint when we see bright light because our eyes have to adjust, the last 6-8hrs we haven’t seen light while we were sleeping. People walk around with aidable losses for 5yrs on average before they do something about it. It’s foolish to flip a switch and give them all this sound. I always warn people the first 2 weeks is what I call survival weeks. I expect you to come in and ask me to give you a little more, but I’m not going to force it down your throat from day one. Get use to hearing some thing through them, get used to physically having them on.

I have never in 15yrs heard a case to utilize DSLm[i/o] for adults as the results have been mixed at best. Again, we predominately use it on pediatric fittings.

#17

In my case, NAL-NL2 was much better than the proprietary bernafon formula “bernafit”. But then again, bernafit is based upon nal-nl1, so maybe isn´t “up-to-date”. Maybe bernafon is working on a formula based on nal-nl2.
I like the NAL-NL2 fitting very much. It gives good amplification for soft sounds (where you need it) and doesn´t hurt your ears at loud sound (when everything is loud enough anyway).

#18

Hi, Musician. I’ve been following your trialing odyssey in your various threads. When you trialed your Phonaks and Siemens did you have them tuned with NAL-NL2 also? Or did your audi use the manufacturers’ proprietary formulas? I am thinking of going back to the audi to ask her to try fitting my Phonaks with NAL-NL2. Do you (or anyone else) think that would be worth a try? Thanks.

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#19

Hi,

with siemens I had both - first the proprietary formula, then nal-nl2, because the siemens technician thought that nal-nl2 might be better for music.

In case of the siemens, there was hard clipping with music, I´m sure. Couldn´t be avoided with any setting.

With phonak I don´t know, but it sounded (from the basic sound) very similar to the siemens with nal-nl2.

Note that nal-nl2 uses very much compression, more amplification of soft sounds, less amplification of louder sounds. This is perfect for my speech understanding.

For music, however, I have programs with less compression. Do you have an open fitting? What kind of music do you make? Maybe you can write me via pn, it gets very complicated here.

Regards,

Musician

#20

I’ve been looking into the differenced between VAC+ and NL2. It’s interesting. Below are the maximum power output, targets, and compression ratios for my audiogram under each fitting rationale. Soft gain is significantly higher in my left ear under NL2, and compression ratios are higher. The thing that puzzles me most is the difference between the two rationales for MPO. Why is NL2’s MPO so much lower almost across the board than VAC+'s? And what would that mean in real terms?

VAC+ Right Left
250 500 750 1k 1.5k 2k 3k 4k 6k 8k 250 500 750 1k 1.5k 2k 3k 4k 6k 8k
MPO 102 106 106 106 105 102 102 102 102 102 102 103 103 103 103 102 102 104 105 101
Loud Gain 0 0 1 2 3 4 5 0 -1 -1 0 0 1 2 3 4 2 -1 -1 -1
Mod. Gain 0 0 1 2 3 4 2 0 1 1 0 0 1 2 3 5 3 2 2 2
Soft Gain 0 0 1 2 4 4 5 2 2 2 0 0 1 2 6 6 10 8 7 7
Mod-Loud Compr. 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.2 1.2 1.0 1.0 1.0 1.0 1.0 1.1 1.1 1.3 1.3 1.3
Soft-Mod. Compr. 1.0 1.0 1.0 1.0 1.0 1.0 1.1 1.1 1.0 1.0 1.0 1.0 1.0 1.0 1.1 1.0 1.3 1.2 1.2 1.2
NL2 Right Left
250 500 750 1k 1.5k 2k 3k 4k 6k 8k 250 500 750 1k 1.5k 2k 3k 4k 6k 8k
MPO 77 87 92 92 93 90 93 97 96 91 80 89 95 95 96 93 98 105 105 96
Loud Gain 0 0 1 2 3 3 4 1 0 0 0 0 1 2 3 3 4 1 0 0
Mod. Gain 0 0 1 2 3 3 4 1 0 0 0 0 1 2 3 3 5 5 5 5
Soft Gain 0 0 1 2 3 5 8 8 7 7 0 0 1 3 6 9 16 16 15 15
Mod-Loud Compr. 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.1 1.4 1.5 1.5
Soft-Mod. Compr. 1.0 1.0 1.0 1.0 1.0 1.0 1.1 1.2 1.2 1.2 1.0 1.0 1.0 1.0 1.1 1.2 1.4 1.4 1.4 1.3