ReplayGain and loudness¶
Why can two tracks have the same peak level but sound different in volume? Peak amplitude and perceived loudness describe different things. ReplayGain stores measured playback adjustments as metadata; a supporting player can use them when playing the audio. Editing those fields is different from measuring the recording or changing the encoded audio samples.
The four common fields¶
| Field | Meaning |
|---|---|
REPLAYGAIN_TRACK_GAIN |
Gain adjustment measured for this track. |
REPLAYGAIN_ALBUM_GAIN |
Gain adjustment measured for the album as a group. |
REPLAYGAIN_TRACK_PEAK |
Peak amplitude recorded for this track. |
REPLAYGAIN_ALBUM_PEAK |
Peak amplitude recorded for the album. |
Track mode levels individual songs. Album mode uses a common adjustment to retain the loudness differences within an album. Negative gain means reduce level; positive gain means increase it. Peak metadata can help a player avoid clipping after gain, subject to its settings. See the ReplayGain specification for the measurement and playback model.
A stored gain is not a volume percentage, a peak reading, or the track's bitrate. Changing the number by hand does not run a loudness analysis. Whether playback uses track gain, album gain, additional preamp gain or no ReplayGain depends on the player. OpenTag's field display is not a playback meter.
Read the stored text before changing it¶
The following values are invented metadata for a practice copy. They are not measurements of the guide's example album and should not be copied to real tracks as a normalization recipe.
| Field | Practice value |
|---|---|
REPLAYGAIN_TRACK_GAIN |
-4.25 dB |
REPLAYGAIN_ALBUM_GAIN |
-3.00 dB |
REPLAYGAIN_TRACK_PEAK |
0.950000 |
REPLAYGAIN_ALBUM_PEAK |
0.990000 |
OpenTag can inspect these stored fields in Extended tags. A custom
column or export can read their placeholders, for example
%replaygain_track_gain%. Unknown text fields use the tag family's supported
custom-field path, so storage and player interpretation can differ by format.
ID3v1 has no general custom-field space for this set. Do not assume that an
arbitrary similarly named field is an alias for another loudness scheme.
For a deliberate metadata correction, Keep changes stages Extended tags edits and Save tags writes them. Actions and converters have their own write timing. Reopen/read back the saved file before deciding that a player's lack of volume change is a failed tag save. It may be ignoring the field or using a different playback mode. Use an audio-analysis tool that supports your target workflow to calculate gains from the recording; this guide's OpenTag workflows edit the stored metadata.
Preservation during MPEG saves has conditions¶
An MP3 can have ReplayGain data in an APEv2 tag while OpenTag displays its
ID3v2 tag. A normal save may remove the APE tag according to Mpeg
preferences. In that path, when ID3v2 is being written, OpenTag has a specific
safeguard: it copies nonempty REPLAYGAIN_ and MP3GAIN_ fields from the
removed, undisplayed APE tag if the full displayed values and existing ID3v2
tag do not already contain that field name. Existing values take precedence;
this is not a conflict-merging or recalculation operation.
These written cases use APE Read off, ID3v2 Read/Write on, APE
Write off and APE Remove on. Each practice file starts with ID3v2
TITLE = Paper Boats; saving ARTIST = Juniper Vale triggers the normal
field-save path.
| APE track gain | Existing ID3v2 track gain | Saved ID3v2 track gain |
|---|---|---|
-4.25 dB |
Absent | -4.25 dB |
-4.25 dB |
-1.50 dB |
-1.50 dB |
| Absent | Absent | Absent |
Do not generalize that safeguard to Remove tag, an explicit field
removal action, a save without an ID3v2 target, or every container format.
A broad keep-list action can erase loudness fields that are not listed.
MP3GAIN_UNDO is another tool's restoration information, not a ReplayGain
track gain or OpenTag's Edit → Undo history. Preserve it when needed.
What this means in OpenTag¶
Before cleaning tags, inspect the actual tag families and stored field names, and retain original files. Keep track and album measurements together where your workflow needs both. If the audio was replaced, edited or transcoded, consider whether the old measurements still describe that recording rather than copying numbers blindly. After an operation, verify the written fields and the receiving player's settings separately.
Removing gain metadata does not itself reverse audio changes made by a different program. OpenTag session undo can restore recorded file operations while available; it does not reconstruct missing analysis or another tool's lost recovery information.