Flac Gain Fix

The most reliable method uses metaflac (FLAC utilities) to remove old tags and replaygain to recompute.

Step 1 – Remove existing ReplayGain tags (optional but recommended):

metaflac --remove-replay-gain *.flac

Step 2 – Compute and add new tags:

metaflac --add-replay-gain *.flac

This automatically calculates both track and album gain using the official ReplayGain algorithm (EBU R128 loudness standard in modern versions).

Step 3 – Verify tags:

metaflac --show-tag=REPLAYGAIN_TRACK_GAIN *.flac

Before we fix the problem, we must understand its root. Volume inconsistencies are not a bug; they are a byproduct of the music industry's mastering history.

For batch processing or integration into scripts: flac gain fix

for f in *.flac; do
    gain=$(sox "$f" -n stat -loudness 2>&1 | grep "Loudness" | awk 'print $2')
    echo "Track: $f, Loudness: $gain"
    # Compute correction relative to -23 LUFS (EBU R128)
done

Note: Manual gain application is discouraged; use ReplayGain tags instead of modifying audio data.

Older ReplayGain tools used a reference level of 89 dB. Newer standards (like EBU R128) use LUFS (Loudness Units relative to Full Scale), often targeting -18 LUFS. Some tools write custom fields like REPLAYGAIN_REFERENCE_LOUDNESS that older players ignore. Your player might be looking for REPLAYGAIN_TRACK_GAIN and REPLAYGAIN_ALBUM_GAIN, but the file has something else. The most reliable method uses metaflac (FLAC utilities)

FLAC stores ReplayGain values in Vorbis comments. The relevant keys are: