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Old 29th May 2012, 12:03   #3
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A 3rd Party ReplayGain Alternative for MP3s Only!

"MP3Gain" is a free program that can analyze and adjust mp3 files so that they have the close to the same overall volume. It is a different implementation of the ReplayGain spec. MP3Gain uses David Robinson's Replay Gain algorithm to calculate how loud the file actually sounds to a human's ears. With MP3Gain, the loudness adjustment is done on the data itself, in a lossless/reversible way. The physical volume is adjusted in 1.5 dB steps. There is no quality lost in the change because MP3Gain adjusts each mp3 file directly, without decoding and re-encoding the file.

Here's the technical reason on why it's lossless (despite operating on the data itself), and also why the smallest change possible is 1.5 dB:

The MP3 format stores the sound information in small chunks called "frames". Each frame represents a fraction of a second of sound. In each frame there is a "global gain" field. This field holds an 8-bit integer which can represent values from 0 to 255.

When an MP3 player decodes the sound in each frame, it uses the "global gain" field to multiply the decoded sound samples by 2^(gain/4). If you add 1 to this field in all of the MP3's sound frames, you effectively multiply the amplitude of the whole file by 2^(1/4) = 119 % = +1.5 dB. Likewise, if you subtract 1 from this field in all of the frames, you effectively multiply the amplitude by 2^(-1/4) = 84 % = -1.5 dB, thereby reducing the amplitude of the whole file.

The way MP3Gain works actually has a very strong benefit. Since it is the "global gain" field data itself that is modified, special support in music players is not required. All music players can play mp3s 'adjusted' by MP3Gain.

MP3Gain can store 'analysis' and 'undo' information in special tags inside the mp3 file. These tags use the APEv2 format. If you choose not to use these tags or delete them with a 3rd party tagger, then you will not be able to use MP3Gain to automatically undo its changes. You will still be able to undo the changes you make, but you will have to do it manually. MP3Gain can make logs of its analysis, changes, and any errors detected. These logs are text files and may have names and storage locations of your choosing. MP3Gain must be used, along with information from the changes logs, to manually undo the changes made with MP3Gain.

MP3Gain provides either Track mode or Album mode analysis and respective overall volume adjustment values. Album mode seeks to maintain the any relative volume level differences between songs, as they are on the real album. To use Album mode correctly, only select the songs that are from the same album when you do the analysis. Both modes may be used for analysis even if there are no tags in the mp3 files, but only a track or an album adjustment can be written to a file.

MP3Gain is very easy to use. Have it load one or more mp3 files or a folder of mp3s and select a track or album mode analysis. As MP3Gain analyzes each file, the results are displayed along with an indication of whether clipping is present in the original file. After all files are analyzed, overall target dB levels (to a tenth of a dB, i.e. xx.x) can then be chosen, before they are applied, to see their effect on clipping. This allows a minimum overall target dB level adjustment to be made when the main goal is to remove clipping in the original file. Of course, the same overall target dB level adjustment (minimum or not) needs to be made to all files when the main goal is overall volume leveling of all files in the group. Additional analysis and adjustments, moving the overall target dB level up or down, can be made at any time.

Use MP3Gain or WA's RG for your mp3s, while it is possible, I don't recommend using both on the same mp3 files. If you use MP3Gain for your mp3s and WA's RG for your other file formats, be sure to set the "Adjustment for files without RG" option to 0 dB or take whatever it's set to into account when you select the MP3Gain overall target dB level for your mp3s.


There is another app with a very similar name. "Mp3Gain PRO" does a different form of volume normalization inside the mp3s. If you feel a song is too quiet or too loud at the beginning (or middle, or end), then it can boost or reduce the volume just for that part. Pretty cool, if that's what you need. In order to make its fine-tuned adjustments, it must re-encode the mp3 file and the changes it makes are not undo-able. For these reasons, I do not recommend Mp3Gain PRO for general use and recommend making a backup of the original mp3 file.

Last edited by Rocker; 19th June 2012 at 02:10.
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