[SloopJon]

> boost the frequencies as necessary

The trick is figuring out what's necessary. The first half of the post made me nervous, because it simply applied a gain of threshold - basedB. As he discovered, that's too loud.

What you want is a compressor. The second half of the post boosts the signal just above the threshold, but it's a little more complex than that. I haven't really studied this, but for starters you want to take into account things like the Fletcher-Munson curves.

I am intrigued by these types of projects. As my hearing gets worse, I'd like to be able to listen to music and watch movies with nice headphones, but with the assistance that comes from hearing aids.