Music-lover's and musician's hearing aids?
This isn't really about headphones, though headphones linked to something like a smart phone app might be part of the solution. Especially since an audiologist told me it is physically impossible to make an ordinary sized hearing aid that produces good undistorted musical sound.
A musician I know is looking into finding good hearing aids for music. Some musicians and music lovers have low frequency hearing loss, some have high frequency hearing loss, and some have a more complicated frequency equalization need, and may also have overall sound sensitivity loss.
This is a major problem for many musicians. Even if you don't play in a loud rock band, many musicians go partially deaf as a result of playing music (in addition to those who go partially deaf for other reasons), or for other reasons. Some try the hearing aids they can find, but are forced to give up, because they can't find anything good enough. It is a common reason for retirement in the musical world.
The problem is so bad that many musicians refuse to play with other musicians who use hearing aids, on the assumption that those hearing aids CAN'T be any good. So one issue that might occur is whether the hearing aid can be hidden, underneath long hair. But perhaps that only affects some musicians.
Likewise, it is a problem for music lovers who want to listen to musical performances. Most hearing aids simply aren't designed for music.
Incidentally, there are a lot of hearing aids nominally advertised for this purpose. Each company claims none of the others do a good job. Unfortunately, for some reason, hearing aids are outrageously expensive. I would guess they are based on signal processing chips that cost a few dollars each at most, but good hearing aids literally cost several thousand dollars per pair. (Health insurance is unlikely to cover hearing aids designed for such a specialized use.) So it isn't very practical to buy a bunch, and test them all. Most musicians are not wealthy. It doesn't help that in the U.S., the FDA regulates hearing aids -which adds greatly to the development cost. Fortunately there is a way around that - "hearing amplifiers" do not have to meet FDA restrictions.
Generally speaking, hearing testing for hearing aids only covers the frequency range of 250-8000 Hz, on the theory that that is most important for understanding human speech, and the rest can be treated as noise that interferes with hearing speech. (I'm a bit confused about how that can really be true, given that typical male human voice fundamental frequency is about 80-200 Hz - but apparently they have decided that the fundamental isn't all that important to understanding speech.) And most hearing aids don't amplify much outside this range - they might only amplify about 200-9000 Hz or so, with substantial roll-off at the ends of that range. A lot of musical instruments go far outside that range. For example, many pipe organs and some extended range pianos go down to about 16-2/3 Hz fundamental frequencies. (There is some question about whether 16+ Hz frequency are actually heard by most people, but you may be able to feel the fundamental even if you can't physically hear it.) And musical instruments go way over 8000 Hz, if you include the overtones - say about 15000-20,000 Hz - higher for some people. So hearing aids designed for speech are nearly useless for music.
On top of that, standard digital hearing aids designed for voice produce many kinds of undesirable artifacts. For example, a good musician should be able to distinguish pitches differing by as little as 1 - 2 hundredths of a semitone (though pitch sensitivity depends a lot on frequency) - much less if you are listening for the beats that occur when out of tune notes are played together - which is a part of nearly all music, because no tuning systems can produce perfect musical intervals between all steps of of a normal musical scale. Most digital hearing aids completely kill such fine frequency distinctions. I don't know exactly how they work, but presumably they more or less identify phonemes, then play back a clearer and louder version of the same phonemes, at very approximately the same pitch and amplified volume. That kills A LOT of fine musical characteristics. Some people try to make do with old-style analog hearing aids, but they still don't support the full musical frequency range.
Another major hearing aid artifact is time delay.
Again, I don't know exactly what frequency equalization algorithm is used in most hearing aids. Obviously, they can't use fourier transforms, because
1. That would impose a huge time delay. You would probably need several frequency cycles of even the lowest pitches to get the data needed to perform the transform.
2. There are abrupt sound changes in both speech and music. You don't want to integrate across sound changes.
But whatever filter is used, it is very important that different frequencies arrive with the same time delay - and for a music performer, that delay had better be very, very small.
By the way, the hearing aid needs a frequency equalization test, that the musician can use to calibrate the device for itself - because the ears have resonances, and the sound chamber created by the ear and the hearing aid (just as with headphones) has very strong resonances, which you want to compensate for, in addition to compensating for the frequency response of the individual's human aural system.
I am tempted to try to create a free or inexpensive smartphone app which takes in the ambient sound (or perhaps mixed sound), applies a filter which implements detailed frequency equalization and sound level compression in accordance with the desires of the musician or music lover, and delivers it to ear buds or a headphone. Possibly to earbuds or headphones which block out the sound reaching them through the air, though you would need really good noise cancellation to block bone conducted sound.
First, does anyone know of an existing free or cheap app, and/or hearing aids, that does a good job, meaning:
1. It preserves full frequency range - say, for example no worse than 20-20,000 Hz, preferably wider.
2. It allows fine grained frequency equalization - say with 20 or 30 frequency bands, and no sudden jumps in frequency response.
3. It preserves fine frequency distinctions, on the order of 1/100 of a semitone, preferably less.
4. It creates the same sound delay for all frequencies, and that delay is very short. (The very short delay is only essential to for music performers, not music lovers.)
5. It does not create any other significant distortion. I.E., no significant harmonic, sub-harmonic, enharmonic, or phase distortion, and very low noise.
6. It picks up very quickly on changes in sound, such as when an instrument tone starts or stops, or when a percussion beat occurs.
7. It performs sound level compression - because one of the aspects of hearing loss is that the difference between the softest and loudest sound levels that you can safely hear is lessened.
8. It does not deliver ads. Imagine the impact on a musician of hearing ads instead of the music in the middle their performance!
Second, if I am to create my own app, does anyone tell me of any good unpatented frequency equalization algorithms that meet those requirements, and where those algorithms are described?
Last edited by MRG1; 05-05-2019 at 06:20 PM.