In Search of Negative Gain

From time to time we see clients clinically who have very significant sensory, and possibly neural, damage. The question always arises in my mind whether to amplify the sound reaching that ear, or to remove the ear from the auditory environment.  There is no clear test for this.  In some cases it can be the result of end-stage Meniere’s disease, and others, it may be related to a sudden sensory neural hearing loss, whether from a skull fracture or an unexplained reason.

One of the first tests that I perform after establishing a significant hearing loss is to walk them over to my clinic piano. The client is asked to play all adjacent notes (white and black keys) from about middle C (a little over 250 Hz) up to the top end of the keyboard (a little over 4000 Hz).  If two adjacent notes do not sound to be a different pitch, then this is evidence of a dead region in the cochlea in that frequency region(s).  For those who don’t have a clinic piano, you can pick up a 1970s style electronic keyboard at almost any garage sale for $5- it’s not the quality of the sound; it’s just a matter of “same” or “different” and for this purpose, a $5 used electronic piano is just as good as a Steinway.  One can also perform the TENS test that was designed by Dr. Brian Moore and this will provide similar information.

However, the clinician is still stuck – do we amplify that region, transpose away from that region, or in the case of many severely damaged frequency regions, do we simply make an earplug for that ear (and perhaps consider a CROS arrangement)? Removal of a severely damaged ear from the listening environment can be very useful especially when listening to, or the playing of music.

 

If I am consulting with another audiologist and have seen this client for a “second opinion”, I have tried to be as encompassing as I could be:“Let’s try amplification, but perhaps we should try attenuation?” Other than this statement providing no direction, are there devices in the marketplace that can provide both amplification on one setting and attenuation, or negative gain, on another setting?

I have been recommending the MusicPro earplug in the past from Etymotic Research.  This is a hearing protector (for loud sounds) as well as a mild hearing amplifier (for soft sounds) that uses a version of the 1988 K-AMP analog circuit.  On one user selectable setting, it provides some amplification, about 5-10 dB,  which would be perfect for listening or playing music, even for someone with a moderate sensory neural hearing loss.  On another user-selectable setting, the MusicPro provides attenuation, or negative gain of 12-15 dB which may be sufficient to remove that damaged ear from the listening environment.

Music Pro insertion gain or loss

A caveat is that the microphone noise may become audible, especially in quieter situations. However, when listening to music, I would be very skeptical if the internal hearing aid noise would reach audibility.  If there is concern, the expansion circuitry can be implemented that would reduce the sound level of the offending internal noise.

Music Pro

This is a low-tech solution to a clinical problem where ultimately the hard of hearing consumer will use that device in a number of situations. In the past, there has been success, with the hard of hearing person using the “negative gain” setting in some situations and slight amplification in others.  There is no clinical test, but the trial period can provide significant information.  Comments such as “I can now hear each of the pipes individually in my pipe organ” are received and that may come from slight amplification or “merely” removing the severely damaged ear from the listening environment.

About Marshall Chasin

Marshall Chasin, AuD, is a clinical and research audiologist who has a special interest in the prevention of hearing loss for musicians, as well as the treatment of those who have hearing loss. I have other special interests such as clarinet and karate, but those may come out in the blog over time.

7 Comments

  1. Hello,

    I had tried the Etymotic Music Pro Plugs, but for my taste they don´t sound good. They give extremely high compression.

    Also, for people with hearing loss (I have a mild to moderate hearing loss, gently sloping down from 10 dB at 200 Hz to 60 dB at 10 kHz) one would need a non-flat frequency response.

    As my hearing aids sound much better than that, I thought if the behaviour of this plug (or better) could be programmed into a hearing aid? With a totally occluded fit (power dome) attenuation should be above 20 dB, so when turned off, the aids should function like an earplug.

    I have already tried out a setup as described above and feel very comfortable with it, but I´m a bit unsure whether it´s really safe. I have Bernafon aids with a raised input range, so the aids only start to distort when it´s really loud. At this point, muting the aids is the only way, but before that, it sounds really good. Also, a quick program change gives the possibility to still understand people talking, which would normally involve taking out the plug and inserting the hearing aid, which is not practical.

    Thank you for your great blog!

    1. Hi Andreas:

      One of the intents of this blog is for people who have a such a severe hearing loss where any amplification at all would be worse than some. Thankfully this is relatively rare and really only occurs for those with hearing losses in excess of 70 dB HL in the higher frequencies (i.e., they have inner hair cell pathology as well as outer hair cell). Given that your worst hearing at 10,000 Hz is about 60 dB I would suggest that this would not be appropriate for you, which I see is your finding as well.

      Best regards, Marshall

      1. Hi Marshall,

        thank you for your kind reply! I had already thought that I might have commented on the wrong blog, but as I was pondering about negative gain as well, I thought I´d give it a try.

        I´m a music teacher, and most of the time I wear open domes. I used to use elacin custom made earplugs as a hearing protection, but since I started wearing aids (ang getting used to them) I´m no longer comfortable with those. Especially because as a teacher I need to talk in between music. I used to coach rock bands, but I gave that up two years ago because of that problem. I am now searching for a solution that allows me to pick up rock music again. But protecting my hearing has absolute priority, so I wanted to have your opinion on whether a hearing aid with negative gain could work as a “high tech” plug. The volumes in questions are, by the way, not extremely loud. The drums are played medium loud (such that an un-amplified grand piano can still be heard), instruments and vocals are amplified to mach the acoustic drum set. But for me, with outer hair cell damage, it´s too loud.

        Besides, the Bernafon aids sound really good for music.

        Thanks again,

        Andreas

  2. More on the piano test. To get more sound from uprights, remember to lift the (hinged) lid–obviously, clear away everything that may be piled on top. Also, roll the piano away from the wall by a foot or so, at an angle. Makes a big difference.

  3. Geez, how do I get my ENT to be this engaged? I wonder if this test using an electronic keyboard and a good set of headphones would be just as valid? Certainly it would eliminate any standing wave issues that you would find in a small room.

    I have had pretty similar loss on both sides until this past year, now one side is much worse. Maybe many months of pain killers from an unrelated surgery are to blame (though of course that doesn’t explain why the loss is not bilateral).

    If I listen to one headphone (ear) at a time, I can easily tell that one side is much worse. When wearing them both I don’t notice that the source has moved from center toward the “good” side, which I would have expected to some degree. The sound still seems pretty well balanced even though the loss on the bad side is 10dB(!) worse.

  4. As soon as hearing degrades, and it appears that assymmetrical /unilateral hearing loss is taking place, the brain goes into “emergency mode” and begins the replication of neural pathways which may or may not be synchronous to the normal, better ear.
    Because of cross patterns of dendrites two possibilities emerge:
    1. The affected brain undergoes neural degeneration, and fragmentation in the processing of all sounds. Hence the poorer ear can never return to its original sensitivity.
    2. Cross hearing patterns at the superior olivary complex has adaptation that allows sounds from the poorer ear to reach the hippocampus of the better ear.
    Item 1 gets irreversibly damaged if no amplification is used from the gitgo. Note that it takes approximately 15-26 years before corrective action is taken by the patient. Hence the neural software in the better ear does a compensatory adaptation, because of the progressive drop in the poorer ear ! In such a case, a Cros device may help with added levels of musical sounds, but localization will still be a problem. Re adaptation at the hippocampus will take a few months to get positive and satisfactory results.

    In Item 2, if a hearing aid is put in the poorer ear, but the loss is 80db and below as a PTA, then one still has a chance for partial recovery of neurons/dendrites, and the beauty of this is that while distortion may remain, the naturalness of incoming sounds will be retained as it also exists in the pre frontal cortex (long term memory). Note that all incomiong sounds are always compared with the memory banks and the result is what we hear. Right?
    A new sound, never heard before will be meaningless and distorted and will have to undergo learning at the hippocampi before storage as long term memory.

    Jay Muhury
    Auditory Neuropsychology
    HAD. (HA 3723)

  5. On the piano test – Room acoustics and placement have a lot to do with how a piano is heard. If the piano is an upright or spinet, and is solidly against a solid wall, that will reduce the treble and bass, because the sound coming off the back of piano’s harp will be muffled by the wall. And this is one reason a grand sounds better, because of the elevation of the piano’s harp, the piano can use the floor as a sound reflecting device. For electronic pianos, the speakers in the device greatly affect the sound quality. The cheap electronic keyboards use speakers that are anything but accurate, so I would discourage using a too cheap one, unless the response at specified db levels, have been verified and compensated for. Some electronic pianos also boost the high end of teh piano sample a bit in an effort to improve the sound coming out of the speakers… If I were to recommend a brand it would be Yamaha.

    Yes, I agree on the need for a “de – amplification” device. Some times things get way too loud. The Etymotics are wonderful for this. Boze has a phase inversion headphone that is great for noisy situations. It simply flips the phase of the incoming sound 180 degrees and blends it back into the headphone’s output. Electronically this is an easy thing to do. But you made a great point here. Thanks for writing this..

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