FLAC gain refers to the relative loudness of an audio file. Unlike lossy formats, FLAC preserves every bit of data, but it doesn't automatically "level" the sound between different albums or tracks. The loudest point in a file.
For power users who want to automate the process via scripts, FFmpeg can be used to analyze and apply gain. flac gain fix
ReplayGain analyzes a FLAC file's loudness and writes a small piece of (a tag) to the file. FLAC gain refers to the relative loudness of an audio file
If you don't like the change, you just delete the tag. FLAC preserves every bit of data
A powerful command-line tool included with the official FLAC package. Use the --add-replay-gain command [19].