What Is ReplayGain and How Does It Work?

A brief look at a non-destructive way to normalize audio 'loudness'

ReplayGain is a standard that measures and compares the loudness of digital audio files. It is intended to normalize audio data in a non-destructive way so that users can listen to digital music libraries without worrying about significant volume fluctuations between songs.

How ReplayGain Works

Traditionally, when normalizing audio, you use an audio-editing program to alter the audio file physically. This is usually achieved by resampling volume peaks, but the technique isn't effective for adjusting the perceived loudness of a recording.

ReplayGain software stores information in the audio file's metadata header rather than directly affecting the original audio information. This metadata allows audio players and sound systems that support ReplayGain to adjust the volume to the desired level automatically.

How ReplayGain Information Is Created

ReplayGain stores information as metadata in a digital audio file. The audio file is first scanned with 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. Measurements of peak audio levels are taken to keep the sound from distorting or clipping.

How You Can Use ReplayGain

The ReplayGain standard can enhance the enjoyment of your digital music library. Many media players are equipped to take advantage of the ReplayGain standard. Here are some ways you can use ReplayGain:

  • Software media players: Some software media players—such as Winamp, Foobar2000, and VLC Media Player—have built-in support for ReplayGain. This is probably the most common way people use ReplayGain.
  • Music management software: If you have an extensive collection of MP3s and use a media application such as MediaMonkey to manage your library, it likely has built-in 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 ReplayGain. This ensures that the loudness levels of your music CDs don't fluctuate as they do when you burn an audio CD normally.

Standalone ReplayGain Software

Applications such as MP3Gain quickly apply ReplayGain values to multiple files. Using these standalone programs, you can typically normalize files singularly (Track Gain) or collectively (Album Gain).

MP3Gain software screenshot

MP3Gain Express works similarly for macOS. It omits some features of MP3Gain, hence the "express" part of the name. Specifically, it doesn't back up your files for you, and it can't be used with video files. It requires OS X 10.6 or later.

MP3Gain Express for macOS screenshot
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