What Is ReplayGain?

A brief look at a non-destructive way of normalizing audio

MP3Gain - Normalize MP3 screenshot

Do you find that the songs in your digital music library all play at different volumes? This variation in loudness can be very annoying when you are listening to songs on your computer, MP3 player, PMP, etc., especially if a quiet song is suddenly followed by a very loud one! To aid in remedying the problem of varying loudness between digital audio files, the ReplayGain standard was developed to normalize audio data in a non-destructive way.

Traditionally, to normalize audio you would need to use an audio editing program to physically alter the audio file data; this is commonly achieved by re-sampling using peak normalization, but this technique isn't very good for adjusting the 'loudness' of a recording.

However, ReplayGain software stores information in the audio file's metadata header rather than directly affecting the original audio information. This specific 'loudness' metadata allows software players and hardware devices (MP3 player etc.) that support ReplayGain to automatically adjust to the correct level which has previously been calculated.

How Is ReplayGain Information Created?

As previously mentioned above, ReplayGain information is stored as metadata in a digital audio file in order for the sound to be correctly played at the right level of loudness. But how is this data generated?

A complete audio file is scanned by a psychoacoustic algorithm to determine the loudness of the audio data. A ReplayGain value is then calculated by measuring the difference between the analyzed loudness and the desired level. The peak audio levels are also measured which is used to keep the sound from distorting or clipping as it is sometimes called.

Examples of How You Can Use ReplayGain

Using ReplayGain via software programs and hardware devices can enhance the enjoyment of your digital music library. It makes it easy to listen to your music collection without having the annoying volume fluctuations between each song. In this section, we'll introduce you to some of the ways you can use ReplayGain. Examples include:

  • Software media players: some software media players such as Winamp, Foobar2000, and VLC Media Player, for example, have built-in support for applying ReplayGain. This method for managing digital music is probably the most popular way people apply ReplayGain values to their collection.
  • MP3 players/PMPs: there's a growing number of portables that can handle digital audio files with ReplayGain metadata. SanDisk, for example, has incorporated this facility into their Sansa Clip and Fuze products.
  • Music management software: if you have a large collection of MP3s and use a media application for managing your library, some of these (like MediaMonkey) comes with native support for ReplayGain.
  • CD/DVD Burning Software: creating audio CDs for use with standard home entertainment equipment can be enhanced if you use burning software that supports ReplainGain. This will ensure that loudness levels of your music CDs (especially custom compilations) don't fluctuate as they might do when burning an audio CD normally.
  • Standalone ReplayGain Software: applications like MP3Gain, AACGain, and others can be used to quickly apply ReplayGain values to multiple files. Using these standalone programs, you can typically process files singularly (track gain) or collectively normalize (Album Gain).