MP3 Diags
Click on in the main window to open this window.
Some transformations are unlikely to be needed by most users. In order to reduce the screen clutter, not all transformations are visible by default. Here you can adjust what you want to be visible.
Note that "Reserve space in ID3V2 for fast tag editing" and "Remove extra space from ID3V2" are shown / hidden automatically according to the state of the "Use fast save in the tag editor" option in the "Others" tab.