−4 dB, −1 dB and −3 dB can all appear in the tags of two songs from one album. There is no contradiction: the first two describe separate track adjustments, while the third can describe a common album adjustment. The player chooses which set to use.
Take two imaginary files from one album. Track one has a track-gain tag of −4 dB; track two has −1 dB. Both have an album-gain tag of −3 dB. The example below shows what changes when a player selects one set of values instead of the other.
Work through the two adjustments
For a simple amplitude adjustment, the multiplier is 10 raised to the power of gain-in-dB divided by 20. Boris Smus's Web Audio API book, chapter 3, explains the amplitude-ratio convention. Applying its inverse gives our rounded figures:
| Gain adjustment | Calculation | Amplitude multiplier |
|---|---|---|
| −4 dB | 10^(−4/20) | 0.631 |
| −1 dB | 10^(−1/20) | 0.891 |
| −3 dB | 10^(−3/20) | 0.708 |
In track mode, the two files get different multipliers. In album mode, each gets the same 0.708 multiplier. A sample value of 0.5 would become about 0.354; a value of 0.25 would become about 0.177. Their two-to-one ratio remains two-to-one.
These are calculated examples, not analysed songs or recommended gain values. They explain why a common album adjustment preserves relative levels, while separate track adjustments can alter the relationship. Player preamp and peak-protection behaviour may add other adjustments; consult the actual controls before applying this simplified example.
The tag and the audio are separate
The official FLAC tool documentation describes an option that calculates ReplayGain information and stores track and album tags. It also documents a separate, non-lossless option for applying gain to the audio. Writing information for playback and changing the samples are different operations.
A player must support the tags to use them. A copied album with a quiet introduction and a louder next track makes a useful first example. Keep the originals aside, scan the copy and inspect both sets of tags. Then check which set the intended player actually reads.
Our album listening exercise provides a simple reason to keep the sequence's level relationships. A shuffled selection of unrelated recordings may give you a different priority.
Streaming has its own control
Spotify's normalization page describes balancing softer and louder songs within its playback system. Follow its instructions for the actual device. That setting does not write ReplayGain tags into your separate personal-file collection.
A level jump between applications can therefore have two different causes to investigate: the streaming setting and the personal-file player setting. Our normalization worksheet records the application, source and output so those paths do not get mixed together.
For an ABX comparison, resolve a level mismatch before starting trials. Otherwise, loudness can supply a clue unrelated to recognising the encoding. Keep the level comfortable; the calculation explains a ratio, not how loudly you should listen.