To adjust the loudness of the tracks according to ITU 1770 standard the Spotify team normalize the entire album at the same time. The softer tracks remain soft as adjusted by the user.
The Spotify team receives the audio at different volume levels. The team uses the loudness normalization to balance the loud and loud songs to create a balanced uniform experience.
The team applies the negative gain to keep the loudness level of -14 dB LUFS. This lowers the volume as compared to the master volume. In this way, no distortion occurs. For softer master team apply the positive gain so the loudness level remains -14 Db LUFS.
To preserve the audio quality team leaves 1dB headroom for lossy encodings. The premium listeners have the opportunity to choose volume normalization levels in-app settings to compensate for a quiet or noisy environment.