lower bitrates after ReplayGain
Reply #6 – 2008-01-27 15:19:51
The initial question was answered correctly by [JAZ] and Seiitsu - if you make an mp3 from two wave files, the same except that one has lower volume level than the other (whether by replaygain tag or hard-alteration from wavegain or some kind of normalization), the mp3 encoded from the quiter wav file will be smaller, because a greater percent of the information in the quieter wav file is below the noise threshold and ignored or encoded less "carefully" (literally, with fewer bits). I believe most or all lossy codecs work this way. This is not a problem. mp3 is a lossy codec. the point of lossy codecs is to package what you can hear conveniently at a smaller filesize, lower bitrate than a wav file. Plenty of people (myself included) like to apply wavegain before encoding to mp3, or use a wavegain value to scale the mp3 in the encoding process. It does mean the file is a bit more lossy (entirely in un-hearable ways except for very quiet parts of music), but it also means is smaller filesize. If you want to make sure you keep everything possible with respect to the noise threshold, encode and apply replaygain or mp3gain after encoding. If not, then encode using the full-volume wav and then apply replaygain or mp3gain to the mp3. Also, retro83 is correct about mp3gain. It will calculate replaygain values, but can also hard-alter the mp3 file (in 1.5dB increments) by raising or lowering the volume. foobar2000 can also do this, by choosing "apply replaygain to mp3 data". This is useful because most hardware players (and lots of programs like WMP) don't recognize replaygain tags. Mp3gain is also reversible - you can just raise the volume back, and it just changes the gain info on each frame of the mp3 file.