The algorithm restores the quality of audio. Model was proposed in this paper and published on github.

There are 3 models available:
1) MP3 Enhancer (by JusperLee) - it restores MP3 files compressed with bitrate 32 kbps up to 128 kbps. It will not work for files with larger bitrate.
2) Universal Super Resolution (by Lew) - it restore higher frequences for any music
3) Vocals Super Resolution (by Lew) - it restore higher frequences and overall quality for any vocals