aacgain : Normalize perceived loudness of AAC audio files ( http://aacgain.altosdesign.com/ )
ardour : Digital Audio Workstation ( https://ardour.org/ )
deadbeef : A music player for *nix-like systems and OSX ( https://github.com/DeaDBeeF-Player/deadbeef )
flactag : A utility for tagging FLAC files via MusicBrainz ( http://software.gently.org.uk/flactag/ )
mp3gain : A program to analyze and adjust MP3 files to same volume ( http://mp3gain.sourceforge.net/ )
picard : Cross-platform music tagger ( https://picard.musicbrainz.org )
r128gain : Fast audio loudness scanner and tagger (ReplayGain v2 / R128) ( https://github.com/desbma/r128gain )
whipper : A Python CD-DA ripper preferring accuracy over speed ( https://github.com/whipper-team/whipper )
Add an ebuild in portage :
The ebuild is now in the portage tree.
You can also use layman : emerge layman then layman -a 4nykey
For Paludis use this rsync : rsync://gentoo.zugaina.org/4nykey-portage
If you have a problem : ycarus(-at-)zugaina.org