The "higher" frequencies make a big difference in understandably, especially with female voices. This has nothing to do with the fundamental or base frequency.

My hearing drops off quite dramatically at about 1.5 Khz. This is not quite enough to understand women and children well. I'm investigating various hearing aides. The modern ones all have essentially something like an audio equalizer (like perhaps on your stereo?) where individual frequency bands can be boosted or attenuated.

I would suggest that your family member go get a hearing test. COSTCO for example will do this for free because they want to sell an expensive hearing aide. The graph of hearing vs frequency will be of a big help in designing software that will actually help.

As an extra comment, when I was in my 20's I could actually hear the 20Khz sonic gizmos that turns lights on/off automatically and they drove me crazy. Not so anymore, but I miss that.

Update: I can't access my old machine right now because the M/B died. However, I remember the sound card having an equalizer function in its driver. It could be that just buying a better sound card than what you have is "the answer" without Perl or any programming required?

Update 2: Because of my own hearing difficulties I've been looking into this further. Apparently there is some freeware for Windows, Windows Equalizer that looks very promising. I have just started playing with the Raspberry Pi and I think there is some software for that critter. Also note that high quality noise cancelling headphones can do wonders versus the speakers.

So far, I haven't found any Perl solutions to your problem. That doesn't mean that there isn't one, just that I haven't found it yet.

Thank you Marshall.

As ExReg said I may have misinterpreted the wikipage on the subject, and got a little more to learn about this issue.
Luckily the flexibility of programming will allow me to easily reparameterize my %CONSTANTS as I learn to fine-tune my solution, so I'm not that worried about the specific values at this time.
I'll also follow your advice of making a full scale equalizer rather than a simple frequency filter, while taking the hearing test results into account for initial parameterization.

A sound card however is not the issue in my case, as the family member I referred to, is not comfortable with computers and watches the videos on a TV screen (via flash drive), which of course in not "open-circuitry". ^^

I'll look into the "Windows Equalizer" when I have a little more free time.
As for noise cancelling headphones, my family member dislikes headphones even more than not hearing properly, but even if that wasn't the case, the main issue is the noise originating from the videos themselves rather than external noises.
Also according to a professional, headphones/hearing-aid could actually worsen the hearing problem at this time, due to nerve entropy.

when(if) I finally finish writing this code, I'll turn it into a new CPAN module (got to learn how to do that too ^^) and add a link to it here, in hope it can assist you and anyone else with hearing problems.

I Thank you, and wish you minimal re-equalizing requirements in the future. ☻

I think you will make speech less easy to understand if you allow only frequencies of 85hz to 255hz to pass. Those are the frequencies listed on https://en.wikipedia.org/wiki/Voice_frequency, but those are the fundamental frequencies and are best for vowels. Most consonants need higher frequencies than those to really understand what is being said. Using that range will give a sound that is like mumbling. I don't hear as well as I used to, and it is definitely the higher ones that I need.

Thank you ExReg.
I guess I have a little more than just the math to learn for this problem.
I'll educate myself a little better before proceeding to the development phase. ^^
Thx again :)

Good luck! I hope you are able to find a workable solution. Try playing with something like Audacity and see what filters might work before putting too much effort into coding. I have had to learn it recently to do some "post production" work and have written code for audio spectral analysis in the past. A lot can be done, but it will probably come via trial and error.

"...developed a hearing problem, making understanding words difficult...compensate for the problem..."

Wouldn't be some good hearing aid device be the better choice instead of such a hack?

Best regards, Karl

Thank you Karl.

Generally this would be the ideal solution, however aside from the unrealistic cost of such a device, a professional has made it clear that at this time, such a device will actually worsen the hearing problem, due to nerve entropy and make daily hearing (which is manageable for now) an issue as well.
Once the hearing problem worsens enough (naturally over time), this solution will be taken into greater account.

Thx.

The best method to accomplish this to buy your family member a good hearing aid.
Because if you fix the video's for one person, the others that hear well may not like the video's sound. That is not a help to them anyway, because they still will not hear well in the outside world.
So getting them a good hearing aid with options they can set, seems like a better solution or some how cure their hearing problem.

Thank you for your suggestion.

I'm afraid that isn't a good solution for my $ituation (see the details in my above replay to Karl),
all technological curing solutions have been exhausted to the extent of my knowledge,
so I'm aiming lower than solving/bypassing the problem as a whole, and focusing on what I think I can do.
Regarding the multiple viewers issue, there isn't an issue, as such a scenario is extremely rare (very different tastes -> rare shared viewing), and everyone got their own device, so watching the original version separately is always an option.

Thank you.

One thing I would keep in mind is. That it was sound that made their hearing go bad, so what you want to do is take the sounds they can hear and make them more audible. That will degrade their hearing even more.
There is new technology's "Auditory brainstem response" that is being used today.

But that will cost money and if your not willing to put any money into it your best bet is to just use some equalizer to tune the sounds to what is audible to the subject. Having hearing damage then their range of sounds will be limited, so an equalizer would be the best bet in this case.