Modify Gain menu

The Modify Gain menu has the following items, which are also available by right-clicking in the file list (note):

Apply Track Gain (Ctrl-G) This will volume-correct all files listed in the File List to match the Target Volume.

Apply Album Gain (Ctrl-B) This will volume-correct all files listed in the File List so that the overall album volume matches the Target Volume.

Apply Constant Gain... (Ctrl-O) This will launch the Constant Gain dialog.

Here you can specify an absolute gain change in dB instead of a Target Volume. Just move the slider until the dB field indicates the amount of gain desired. Increments are in 1.5 dB.
You can also apply gain to just the right or left channel if the mp3 is stereo or dual-channel. Check the Apply to only one channel box and then choose which channel by clicking the radio button beside the desired channel.

Apply Max No-clip Gain for Each file (Ctrl-X) (Only visible when Maximizing features are enabled)
This will change the gain on each mp3 file so that it is as loud as possible without clipping.
NOTE - This is not a good way to make all your mp3s the same volume. Different mp3s can have very different ratios between their maximum amplitude and their average amplitude.
But if you don't care about volume differences between your mp3s and just want them each to be as loud as possible, then this is the function to use.

Apply Max No-clip Gain for Album (Ctrl-L) (Only visible when Maximizing features are enabled)
This will look at each folder in the file list, find the single maximum gain which will not cause any clipping in any of the mp3s in the folder, and then apply that single gain change to all the mp3s in the folder.
I use this feature myself when burning mix CDs of my mp3s. I copy all the mp3s that will be on the CD into one folder, do Track Gain on the folder, and then use this function on the folder. This way, the mp3s are all the same volume, but the whole CD will be as loud as possible without any of the mp3s clipping.

Undo Gain changes If tags are enabled (i.e. "Options - Tags - Ignore" is not checked), then selecting this menu option will undo all gain changes to the mp3 files in the list

(note) - When you use the right-click popup menu, MP3Gain will only perform the chosen function on files that are currently selected in the File List.

Apply Track Gain (Ctrl-G)	This will volume-correct all files listed in the File List to match the Target Volume.
Apply Album Gain (Ctrl-B)	This will volume-correct all files listed in the File List so that the overall album volume matches the Target Volume.
Apply Constant Gain... (Ctrl-O)	This will launch the Constant Gain dialog. Here you can specify an absolute gain change in dB instead of a Target Volume. Just move the slider until the dB field indicates the amount of gain desired. Increments are in 1.5 dB. You can also apply gain to just the right or left channel if the mp3 is stereo or dual-channel. Check the Apply to only one channel box and then choose which channel by clicking the radio button beside the desired channel.
Apply Max No-clip Gain for Each file (Ctrl-X)	(Only visible when Maximizing features are enabled) This will change the gain on each mp3 file so that it is as loud as possible without clipping. NOTE - This is not a good way to make all your mp3s the same volume. Different mp3s can have very different ratios between their maximum amplitude and their average amplitude. But if you don't care about volume differences between your mp3s and just want them each to be as loud as possible, then this is the function to use.
Apply Max No-clip Gain for Album (Ctrl-L)	(Only visible when Maximizing features are enabled) This will look at each folder in the file list, find the single maximum gain which will not cause any clipping in any of the mp3s in the folder, and then apply that single gain change to all the mp3s in the folder. I use this feature myself when burning mix CDs of my mp3s. I copy all the mp3s that will be on the CD into one folder, do Track Gain on the folder, and then use this function on the folder. This way, the mp3s are all the same volume, but the whole CD will be as loud as possible without any of the mp3s clipping.
Undo Gain changes	If tags are enabled (i.e. "Options - Tags - Ignore" is not checked), then selecting this menu option will undo all gain changes to the mp3 files in the list