I want to increase the volume of some mp3 files that I have. Are there any methods of doing this in a lossless way without recompressing the mp3 files and thus decreasing their quality?
mp3ファイルの容量を無損失で増やすことはできますか？
答え
SuperUser投稿者Mokubaiは私たちの答えを持っています：
Yes, you can do this. The technique is used by a number of programs and the levels are calculated by an algorithm called ReplayGain. MP3 volume level data can be adjusted losslessly, just as a JPEG picture can be losslessly rotated. There are two methods:
Calculate the volume level of the file and add a new tag, letting compatible programs adjust the volume on the fly.
Calculate the volume level and adjust a multiplier level in the mp3’s data.
From HydrogenAudio (Implementations):
The second method does alter your file, but because the underlying data is not modified it loses no quality, hence the adjustment can be done losslessly. It is not generally recommended for your main collection as it is modifying the files from their original state, but it can be very useful for portable media players.
A program called MP3Gain can perform the second option and reversibly adjust the volume of mp3s. It does absolutely no re-encoding and simply adjusts magnitude values in the mp3 file itself to change the volume.
From HydrogenAudio (ReplayGain):
Due to the way mp3 files are encoded, the adjustment is limited to 1.5dB steps, which is usually enough to get close. Foobar2000 also includes this functionality and can apply the changes to the files.
