There was a similar forum thread in 2007, but 19 years have passed since then.
I have a phonograph recording from 1890 (Kossuth speech), which I have managed to clean out from very disturbing noises, so I now I have a recording (mp3) that is mostly intelligible. (I can give you the YouTube link in my first reply.)
The voice has a high pitch and sounds like someone speaking from a deep water well.
Do you have any idea how to further improve the quality of my sound?
Here is the result of my noise filtering efforts.
I don’t have any experience in manipulating / improving a recording - but you should consider one point:
mp3 is a “lossy”, compressed format. Whenever you load it, change something and then export again in mp3, you lose on quality. You are better off exporting to a format which does not use any compression, such as .wav or .aiff, etc.
You also could also use the “original” Audacity project files - but the risk is that they cannot be opened / used because they are not as “stable” as .aiff, .wav, etc. So, even if you want to work with the Audacity project files, make a copy in a non-lossy format as well.
I forgot to mention that I also have the wav file, and yes, I do most of these tasks on wav files.
AI is getting better every day so try Googling “AI audio restoration”.