Using mp3gain to change songs to be same volume 

you mean "morbillion". Sorry - 2022 joke ...

Every song/folder you equalize stays where they are on your PC.

It depends on your iTunes settings - under Advanced there's "Copy files to iTunes Media folder when adding to library". If that is NOT set, it probably won't matter. If it IS set (checkmarked), then you need to run MP3 gain on the files in the iTunes media folder AND in the original folder(s) (if you have the mp3s in both places). Also note that if you have enabled the "Sound Check" setting on the Playback tab of iTunes preferences that iTunes will probably ignore/override whatever mp3gain does as iTunes applies its own algorithm. FWIW, The way I do it is I generally rip or download new songs into a work folder and do all my prep work (mp3gain, tagging, trimming silence) there before moving the files to their ultimate locations within my library. That makes it easier/faster to just work with new songs as I add them.

Steve Rothkin, thanks for your detailed and helpful answer to my question. I'm looking forward to applying this app to my music. Cheers. Stu.

Same problem and i still found no solution

Just a spitball: I’d guess that the song that’s too quiet has a big peak somewhere. I’m sure we have all seen random extraneous peaks in waveforms. And that’s making the software thing that it’s a louder song than it really is. Your comment is very old have you found a better solution?

Its similar to what happens when you turn the volume on your stereo up too high and the music distorts when it gets loud (typically because the amplifier "clips" the portion of the signal that exceeds its abilities). The clipping effectively changes the frequencies of what is played so that what you hear is no longer the original. Not everything gets clipped and not by the same amount -- it will continuously vary over time as the the magnitude of the signal changes. Its the same for MP3s - there's a maximum volume level an MP3 can represent. When you raise the "volume" on the entire MP3 file too much, some of the file would exceed the max and will be clipped. If you have undo enabled (which makes the gain settings just like a raised volume control knob in the mp3 file without changing the recording), you will be able to simply be able to reduce the level and redo the MP3 gain. If you have undo disabled, then you will not be able to get rid of the distortion (unless you have a copy of the mp3 from before mp3gain) as the sound has already been changed. There's a decent explanation at en.wikipedia.org/wiki/Clipping_(audio) BTW, 105dB is probably way too high - almost guaranteed to result in clipping. I certainly wouldn't go above 95. But you will have to go even lower for music with a wide dynamic range. That's why I settled on 89.

yeah it works for me...not sure why its not for you

it can depend on the music player you use, try turning on options/tags/ignore.

it does. download 1.3.4 version

MP3Gain Pro is a different program by a different author. You need to download the original FREE mp3gain from mp3gain.sourceforge.net/. There you will also see what the original author has to say about MP3Gain Pro.