I don't think anyone has yet actually described the technical difference between MP3Gain and ReplayGain, so I'll try and give the details...
As I'm sure you all know, an MP3 file is a sequence of "frames". As well as the audio data, each frame also contains a header, and one attribute in the header tells the replay device at what level to output the frame. MP3Gain updates this attribute in the header of every frame in the file, in order to adjust the playback level up or down. Note that the actual audio is not updated, just the instruction as to what level it should be. Therefore it's a lossless adjustment. Recent versions of MP3Gain also add a comment in the file's metadata to indicate by what amount it has adjusted the level, so that it can be undone. In contrast, ReplayGain does not alter the headers in the individual frames, but simply writes some tags in the file's metadata to indicate what amount of playback level adjustment should be made. As it happens, the same algorithm is used by ReplayGain and MP3Gain to calculate what the appropriate level change should be. The advantage of MP3Gain is that since the actual frame headers are changed, the loudness equalisation effect works on ALL replay devices. The disadvantage is that only one level change can be applied (ie. you can ask for track gain, or album gain, but not both). On the other hand, ReplayGain can add multiple tags, to allow for different level changes for different playback scenarios (ie. it can add tags for both track gain and album gain). But the disadvantage is that the replay device needs to understand the ReplayGain tags in order to apply the level change. If you MP3Gain *and* ReplayGain a file, and then play it back through a device that understands ReplayGain tags, then the playback level adjustment will be applied twice. -- cliveb _______________________________________________ Discuss mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/discuss
