Sorry if it was before a similar topic, but i am use first time replaygain function.
I guess that replaygain function reduce a little bit DR (dynamic range) or maybe i am wrong.
ReplayGain runs a scan to determine how loud a track sounds.
The original idea was for the ReplayGain info to be saved to each file in a tag, which the player would read and use to adjust the volume on playback. There's no compression. Each track is simply adjusted up or down by a specific amount. FB2K will adjust the volume that way.
As support for reading ReplayGain tags is a bit scarce for hardware players, the alternative is to physically adjust the volume of the track. The volume of MP3 and AAC can be adjusted losslessly (you don't have to re-encode) by changing the volume data in each audio frame. That's what Mp3Gain does. It scans the audio, saves the ReplayGain info and you can use it to adjust the volume losslessly. If you do, the ReplayGain tags will also be updated to reflect the new volume. The standard ReplayGain target volume is 89dB (don't change it unless you have a good reason), which is actually a sound pressure level, so somewhat meaningless, but it translates to -18dB (the level on your player's output meter, where 0dB is maximum). If the result of a ReplayGain scan says +3dB (for example) it means the volume needs to be increased by 3dB in order to achieve the ReplayGain target volume of 89dB. The info saved to tags is always relative to 89dB.
FB2K can scan and save the ReplayGain info to tags, use it to adjust the volume on playback and/or to adjust the volume losslessly as MP3Gain does, only it'll adjust MP3 and AAC in an MP4/M4A or MKV container (and possibly others) whereas MP3Gain only works with MP3 files and raw AAC. Fb2k can also use the ReplayGain info to adjust the volume when converting audio, and it uses a newer scanner which is probably a little more accurate than the original ReplayGain scanner (in case you wonder why FB2K and MP3Gain never exactly agree on volume).
Mp3Gain saves the info to a different type of tag than FB2k, but it also saves undo information to reverse the volume change, whereas FB2K doesn't. Mp3Gain is oblivious to any ReplayGain tags FB2K writes, whereas FB2K is aware of MP3Gain tags and will update them if you use FB2K to scan files already scanned with Mp3Gain.
Yetanotherid, thank you very much.