eplay Gain (ReplayGain, Replaygain) - a standard for presenting information that allows audio players using it to automatically “soften” the output signal to play different audio files at the same volume level.

Using Replay Gain allows you to avoid manually changing the volume level when playing audio files from different albums / discs recorded with different volume levels.

Replay Gain involves scanning the entire file using psychoacoustic analysis to determine perceived loudness and peak levels.

Another advantage of using Replay Gain is that using peak levels avoids “trimming” songs at high volume.

Typically, a Replay Gain is stored in the audio files as metadata.

Replay Gain implementations usually only add metadata to the audio file without changing the original data. Despite the fact that the Replay Gain standard defines the use of an 8-byte field in the file header, many popular audio formats, such as Ogg Vorbis and FLAC, use tags to store Replay Gain information. Moreover, the most common way to store this information in MP3s is to write APEv2 tags to the end of the file.

Another way to implement this standard is to either directly change the volume level in the scanned file, or create a copy with the modified sound from the original file. As a result, this process may not be completely reversible.

Winamp, Foobar2000, Rhythmbox, Audacious, Amarok 2.1, Quod Libet, and AIMP players support this standard by default.

Rockbox is free software to replace the firmware of digital audio players. The Rockbox project began at the end of 2001 and was first implemented on the Archos Studio player.

Rockbox offers an alternative to the player’s firmware, in many cases, without removing the original firmware. Rockbox's internal device allows for increased functionality through the use of expansion modules. Improving functionality includes applications, utilities, and games. Rockbox can provide (retrofit) video playback for players released in the mid-2000s. Rockbox also has a voice-driven user interface suitable for use by people with blindness or impaired vision.

When installing Rockbox in many cases, it is not necessary to write it to flash memory instead of the factory firmware. Instead, a small bootloader is written to the memory, which allows you to choose whether to launch Rockbox or factory firmware.

Rockbox works on a wide variety of sound devices with very different hardware capabilities: from early Archos with their primitive displays to modern players with great picture clarity, digital audio and recording capabilities.

Typically, official firmware is superior to Rockbox only in support of WMA and DRM. They can also have the function of good and accurate rewind, with the ability to hear the stretched area. At the same time, on many players Rockbox is not able to take on all the functions of the original firmware, such as downloading files to the player, recharging.