You know the problem: a quiet acoustic track ends, a loud remaster begins, and you lunge for the volume. The cause is the "loudness war" — albums mastered at wildly different levels over the decades. ReplayGain is the long-standing fix, and unlike a blunt volume limiter it adjusts playback intelligently without touching your files.
Why Volume Jumps Between Tracks
Loudness is a mastering choice, not a fixed property of music. A 1980s jazz record and a modern pop single can differ by 10 dB or more in perceived level. Shuffle a mixed library and those differences become a constant annoyance. The files are fine; what is missing is a shared reference level so they all play at a comparable loudness.
How ReplayGain Works
ReplayGain scans each track and measures its perceived loudness using a model of how humans actually hear, then stores a small gain value — how much to turn that track up or down to hit a standard reference level. At playback, the player applies that gain. Nothing is re-encoded; the adjustment is applied on the fly, so your original files stay bit-perfect.
Track Gain vs Album Gain
ReplayGain offers two modes. Track gain levels every song independently, ideal for shuffle and playlists. Album gain applies one adjustment across a whole album, preserving the intentional loud-and-quiet dynamics the artist built between songs — essential for records meant to be heard front to back. Good players let you pick per context.
ReplayGain vs Sound Check and Limiters
Apple’s Sound Check is a similar idea with less control and a closed implementation. A simple limiter or compressor, by contrast, squashes dynamics to force a constant level — that hurts sound quality. ReplayGain is gentler: it only shifts the overall level of each track, leaving the dynamics inside the music untouched. With a preamp setting you can also avoid clipping when gain is applied.
Scanning Your Own Library
Commercial downloads sometimes ship with ReplayGain tags already embedded, but ripped CDs and older files usually do not. That is where a built-in loudness scanner matters: it analyzes your collection once and writes the gain values so every future playback is balanced. The scan is a background task; the payoff is permanent.
Even Loudness in PhaseShift
PhaseShift includes ReplayGain with built-in loudness scanning, so you can level your whole library — track or album mode — and stop chasing the volume knob. Paired with gapless playback and a safety preamp, it keeps a mixed collection comfortable to listen to for hours without ever recompressing a file.