If you'd like to enable HD music playback when using the Spotify app in offline mode, this trick will teach you how to do so.
Here are the instructions on how to adjust sync quality in the Spotify app. This setting will determine the sound quality of your offline music files.
How To Listen to HD Offline Music on Spotify
Open the Spotify app and tap on Menu > Settings > Playback > Sync Quality. By default, Sync Quality is set to Normal, but other presets such as High and Extreme are also available.
By switching to High or Extreme , you'll enable the app to sync HD versions of music tracks. The only downside is that HD files are heavier in size and require more storage space.
Before leaving the Settings menu, don't forget to toggle the Sync over Cellular switch to Off. This will set the Spotify app to sync files only when connected to WiFi, thus reducing your mobile data usage.