Crossfading is handled by the AutoDJ provider which by default, and by our recommendation is Liquidsoap. Four options are provided with Liquidsoap AutoDJ being Fade-in, Fade-out, Smart Crossfade and Minimum Threshold.
Crossfade Duration & Threshold
When not using Smart Crossfade, tracks will in sequence Fade-Out and then Fade-In without any blend or mixing. Crossfade can be disabled by setting both of these options to 0.
The Minimum Threshold option checks the upcoming track and if the next track duration is less than the threshold, crossfading will be applied between the current and next track. The crossfade would not apply to the end of the track, unless the next track was also short. Setting this option to 0 will ensure transitions on all tracks.
Smart Crossfade
Smart Crossfade will automatically attempt to calculate the volume between tracks to produce an optimal transition. For example, should Track A include a soft fade at the end and Track B a loud start, Smart Crossfade would not fade-out and only fade-in. Read more about Smart Crossfade. Often tracks may already include a fade-out built into the media file, and in this case Smart Crossfade will be useful to avoid double ups in the crossfading transition.
Replay Gain Adjustment
The Replay Gain Adjustment feature works by checking the metadata on uploaded audio files for REPLAYGAIN_* metadata and adjusting playback using this metadata to normalize the volume of the audio stream. Enabling the feature will apply it across the entire service for AutoDJ tracks and will use more CPU.
You can read about the ReplayGain standard on the Hydrogenaudio Wiki.
