Just discovered FFmpeg suite.

[Geek-9pm]

Just want everybody else to know.
For years I have worked with Audio files  and have used different software tools.
Somehow, I had never heard of FFmpeg freeware.
Thanks to Samson Trout foretelling me.
Here are two relevant links:
https://www.ffmpeg.org/
https://en.wikipedia.org/wiki/FFmpeg

For Video tutorials, there are many on YouTube just for FFmpeg.
Here is one:
https://www.youtube.com/watch?v=MPV7JXTWPWI
 

[Salmon Trout]

Ffmpeg can process video as well as audio, in fact many people mainly use it for video. Many, many of the "Free video converter" software apps on the web are no more than GUI "front ends" with ffmpeg doing all the work behind the scenes. Mostly they do not give credit to Fabrice Bellard, its creator. One that does is Handbrake, which is widely used.

Zeranoe has Windows and Mac ready-made builds of ffmpeg, updated every few days.

https://ffmpeg.zeranoe.com/builds/

You can get packages for Linux, even for the Raspberry Pi, but you may have to compile from source.

[Geek-9pm]

For reference:
https://superuser.com/questions/323119/how-can-i-normalize-audio-using-ffmpeg
That is the link Salmon Trout gave me earlier.
Very impressive.  The FFmpeg program has at least three different ways to correct levels in any audio file.
This is professional grade software for free.

I plan to use it in a batch file to correct all the MP3 files in folder. 

[patio]

"Samson Trout" ? ?

[Geek-9pm]

"Samson Trout" ? ?

Did I say that? 

[Salmon Trout]

"Samson Trout" ? ?

Better not cut my hair

[nil]

sounds like a cool program, i'll check it out!

[patio]

Better not cut my hair

    

[Salmon Trout]

   

But first Delilah...