This is a serious question and something ive been wondering for a while now. If a hearing aid gives you as much gain as your hearing loss, does it completely cancel your loss and therefore result in you being aided to 0db? Say someone has 70db hearing loss and wears a hearing aid programmed for 70db gain(which may not even be the max gain the HA is capable of!) would he have an aided score of 0db? If not, what could be the reasons?
No. If this were the case, you would walk into your HA fitting with your audiogram. It would be fit with a gain that perfectly matches your audiogram and you would have normal hearing. There would be no need for fancy algorithms.
The reality is there are a multitude of factors that make this true. The first one that comes to mind is signal to noise ratio. Someone with normal hearing may have 70dB of comfortable listening range. If your audiogram shows your pure tones at 60dB, you probably only have about 40dB of usable range. Your instruments job is to fit that 70dB that everyone else has into the 40dB that you have while not distorting the sound, no small task!
I would only add that it is often not necessary or desireable to completely correct for hearing loss. In my case, my loss at 3 - 4KHz is 35 - 40dB worse than at 1KHz but, in practice, I find that my word comprehension approaches 100% with only 12 - 15 dB of additional correction (at high frequencies) and more is too loud.
It is possible to put sounds of different loudness close to each other so that the sound quality is good. I have such fitting and it sounds good and natural. Iāll include my fitting graph in this message, itās an output graph. The hearing aids are Phonak microSavia 100 dSZ with micromolds. Pink lines are the unaided curves, and blue lines stand for incoming 40 dB (bottom), 60 dB (middle) and 80 dB (top) sounds. The black line is mpo (maximum power output). I donāt even notice that different loudnesses have been taken closer, other than itās more comfortable. Iāve had normal good hearing in the past.
For what Iāve heard itās difficult to get to 0 dB because of the circuit noise of hearing aids, which is somewhere between 0-20 dB.
My hearing numbers:
Freq/Left-Right
125 / 55 - 65
250 / 55 - 70
500 / 55 - 60
1000/ 55 - 65
2000/ 50 - 60
3000/ 35 - 45
4000/ 25 - 35
6000/ 25 - 35
8000/ 25 - 35
Kind regards,
Leia
Somewhere I read if say you have a 70 db loss if you can get that down to 35 db you have maxed out the expected gain in the real world. As noted a full correction can be counter productivity even if possible.
For an X dB sensorineural (nerve) loss you need around X/2 or X/3 dB gain ā¦ NOT the full X dB gain.
For an X dB conductive loss you DO need X dB gain.
(Conductive losses are however relatively rare)
Something that has to be figured in, I would think, would be the volume of the original sound. I understand that you have the original sound, that sound at whatever frequency can have added so much gain , basically add the 2 together and you have output.
Something I do not have a grasp of is , you have an incoming sound 60 db soft speech,it is energy and is real. That sound is digitalized, analyzed and for instance has 50 db of gain added. My assumption has always been that that makes for an output of 110. I have always thought that the aids digital to analog converter is producing energy for that gain portion and that the original sound/energy is dealt with as it is. Minus that guessed at insertion loss.
Or is the aid taking that original energy digitalizing it adding to it gain wise and the output energy is a new 110db of completely remade sound, energy.
Itās a bit of a mistake to think of a sensorineural hearing loss as being a āloss of volumeā that can simply be compensated by a āgain of volumeā.
In the cochlea are an array of tiny hairs which conduct sound patterns to nerve receptors, which then send signals to your brain. The brain receives the signal patterns and interprets them as sounds. Itās somewhat analogous to the old crawler signs at your local bank that would display the time and temperature as a pattern of dots ā your eyes would see the dots, and your brain would then interpret those patterns as letters or numbers.
In a sensorineural hearing loss, some of the hairs and/or nerve receptors that pick up the sound patterns are non-functional. Thus your brain no longer has as clear a pattern from which to interpret sounds, especially verbal communication. Itās like having some of the light bulbs in the crawler signs burned out, so that you have difficulty distinguishing between a ā8ā and a ā3ā or the letter āBā. No matter how bright you make the remaining lights, the information simply isnāt there.
Hearing aids are about increasing your signal-to-noise ratio so that your brain has a better chance to process what information it has remaining. They canāt completely compensate for the information that is lost. That is why a person with a 70-80 dB hearing loss (such as myself) can hear voices perfectly well with hearing aids, but has trouble actually understanding them.
Why not use linear amplification starting at 0db HL then? What other factors are there? As for signal to noise ratio, I thought HAs canāt improve this, only offer amplification?
Do you have an audiogram to give us a better idea?
For what Iāve heard itās difficult to get to 0 dB because of the circuit noise of hearing aids, which is somewhere between 0-20 dB.
You have an unusual low frequency loss, did Menieres cause this loss? You raise a good point regarding circuit noise. I donāt know the relationship between circuit noise and gain and in which frequency causes more circuit noise. Id like to learn about this! Do CI have circuit noise too? Ive seen 2 people so far with CI who hear at 0db in 1 or more frequencies.
You both discuss the half gain rule. What happens if you give more than that? Ive always been given maximum gain. My 1998 audiogram showed 100db HL and 35db HL with HAs for a gain of 65db. A gain of 50db would put me outside the speech banana and unable to hear any speech. Id also be missing out on alot of sounds and everything would be way too quiet. Many people get closer to 2/3 gain than 1/2 gain, wouldnāt 2/3 gain work better?
As for conductive losses, are they attempted to be aided to 0db or only the amount that the air-bone gap shows? Why would it be different for mild-moderate SNHL? The OHCās are basically biological amplifiers anyway.
up to 60db HL, the damage involves the OHC(not IHC) which results in very little loss of information/clarity. So why not give a gain equal to a HL limited to OHC damage? As for IHC, you are correct that youd start missing information and experiencing distortion. Perhaps give the same 60db gain for all HL of 60db or worse. At least a 60db gain can replace the natural amplifiers your OHC once had to a large extent. Nothing can be done for the IHC. More than 60db gain should still help for environmental sounds and speech awareness, but probably will do little to improve speech comphrension. Youd be making the existing lights brighter for sounds though.
How much gain do you have, do you have an audiogram? Couldnāt you be aided to 10db with 70db gain? It may not improve clarity but itll let you hear so many more sounds and youd hear speech from the other side of the house(double the distance requires +6db gain) Also what was your speech discrimination score for words, sentences, etc? Ive read that youd hear with properly programmed HAs equal or slightly better than the average CI.
deaf123, your questions are entering the academic area.
This in not an audiology blog, itās a forum for hearing aid users.
Perhaps you should sign up for an audiology course somewhere?
IF Deaf123 did that, then I wouldnāt be learning about a very interesting subjectā¦
I second that.
Deaf123ās thoughts are fascinating.
There is lots of stuff going on in the mammalian hearing systems. And lots of stuff can go wrong. Itās not just hair cellsā¦its also the neuronal system and all that stuff (Olivary, Brain stem, Thalamus, etc.) in between the hair cell and the auditory cortex.
On a technical basis when we say a person has 50 db loss at X frequency, we mean that reference a normal personās hearing, a sound must be 50db SPL louder to be perceived. SPL is the standard measure of loudness. 0db SPL refers to the softest sound a normal person can hearā¦very faint like the buzz of a mosquito or leaves in a soft wind. Iām sure everyone is aware that an increase of just 3db SPL means doubling the sound pressure.
Now if we kick the hearing aid gain up to 50db, the rated loss, then at normal average speech level which is approx. 60db SPL at one meter, we will come out of the aidās receiver into the canal at 50 + 60 = 110db SPL which is really highā¦getting up to the threshold of pain. As a practical matter such a level may be intolerable. Experience has shown that 1/2 the db loss is usually the max gain that produces the max comprehension and depending on the amount of recruitment, reasonable comfort.
So as previously posted, the function of a hearing aid is to fit speech etc. into a impaired hearing system which has limited (dynamic range) between the softest sound they can hear to the loudest sound that is comfortable. This calls for non-linear amplification of some kind. Ed
I think of the 50% rule of thumb referring to āfunctionalā hearing and really if not directly related to db results.
Two people may see 20/20 yet oneās vision may be ābetterā than that of the other person. Brain processing function can be as important if not more than the volume/clarity of the sound source. In vision we know two people with 20/20 vision standing side by viewing an accident can get on the witness stand and tell to very different accounts of what they witnessed. Since my background is vision I tend to draw on that understanding which may not be one for one but it is my frame of referrence.
The signal to noise ratio I was referring to was your hearing, not the instrument. Yes, HAs can only offer amplification. Linear amplification is very limited becuase as Ed mentioned, if you have a 70dB loss and sound is 60 dB, that would require 130dB to be produced by the instrument. This would be way too loud; even though you have a 70dB loss, at 100dB or so, things are still too loud. Instead the instrument would decide that it is going to not use the normal 70dB gain you may want and instead only give you 30 dB for this loud sound and deliver 100dB, this is the basic idea behind compression.
Setting compression is a good example of where we self programmers really cannot match the experience of a top notch fitter. Attack and release times, where to set the knees and how deep is certainly not a topic this is simply reconciled by the casual user!
Note that these are WDRC variables. ADRO does not use them. Ordinary folks can accomplish a first order ADRO fitting, using a āhearing testā that establishes ācomfortableā sound levels for each frequency band. This initial fitting can be refined by (A) listening to loud sounds to adjust the Maximum Output Level and (B) listening to soft sounds to adjust the Maximum Gain levels. The user really only has to make judgements about how well he can hear sounds and recognize words.
However, it is mainly the āease of use factorā of the programming software that would prevent the average person, with mild/moderate hearing loss, from adjusting his own hearing aid. As any computer savy person knows, operations can range from insanely complicated to butt simple, depending on the geek-factor of the user interface. āKeep it Simple!ā for success. 
lets see, it depends- if you have a conductive loss. Your entire dinamic range will be shifted by about 70db. Thus a 70db gain will be the most appropiate.
If the loss is senso. then as a very crude estimate we use 3 rules, 1/3, 1/2 and 2/3
for mild to md./ mod to sever / and sev to prof.
Ofcourse now fitt form are more refine, so this should be used for a very crude
calculation
I think erainwaterās comments are most welcome even if they do border on the academic. Iāve absorbed a good deal from the explanations of why just increasing the volume doesnāt help in a lot of situations. The hairs in the cochlea Iāve understood before but there were some organs mentioned that I didnāt realize had such a bearing on hearing/understanding. Interesting! I had a slight stroke 4/5 years ago in the basal ganglia but didnāt think that would cause confusion in hearing. However, Iām pleased to know that other organs in the brain have a bearing on understanding as well. Thanx. 
I donāt mean to come across as negative in my posts ā¦ itās just that Iām a bit cautious about enthusiastic amateurs.
People tend to believe that they are experts when they get to the 10% or 15% knowledge level for a topic ā¦ and this is when REAL mistakes can occur.
People with 0% knowledge know their limitations and so proceed very cautiously.
People with 80%+ knowledge plus a reasonable amount of real world experience of working with MANY hearing aid users also have a different world-view ā¦ which generally does NOT focus on ādBā or āReal Ear Measurementsā or āVisible Speechā or whatever.
Supplying & fitting a hearing aid requires a blend of hard-won skills ā¦ which means that an experienced dispenser will tend to twitch when a client starts replaying stuff he/she has read on the Web or in a marketing brochure.
Example: a client can arrive and state that according to their Web research the Audeo IX with Sound Recover is the aid for them. They present their ācaseā with Web page & PDF printouts. I then find that they have a flat conductive hearing loss overlaying a perfectly normal cochlear response. A simple high power linear aid will suffice in such a case.
At this point I smile sweetly and explain the whole situation so that the client understands whatās going on and what the options are.
I do however sometimes feel that itās a little disrespectful for people who have spent 4 or 5 hours on the web to tell someone who has spent several years, 5 days a week, 10 hours a day working on the topic what āthe perfect solutionā is.
Now how would YOU react in such a case?
And how would your cardiologist react if you explained āthe optionsā to him/her?
PS I believe that there is a book which covers these sort of points: The Cult of the Amateur: How Todayās Internet is Killing Our Culture
I am interested in where your focus is, then. As a computer guy, I do agree that experience changes the focus and blurs the lines quite a bit - I have seen this many times.
As a hearing aid user Iād love to hear the general strategies in use by an experienced fitter. I realize that these wonāt make me an instant expert, but (if you decide to share) they will quite likely be of great value anyway!