• For popularity>0, we got close to all tracks on the platform. The quality is the original OGG Vorbis at 160kbit/s. Metadata was added without reencoding the audio (and an archive of diff files is available to reconstruct the original files from Spotify, as well as a metadata file with original hashes and checksums).

• For popularity=0, we got files representing about half the number of listens (either original or a copy with the same ISRC). The audio is reencoded to [OGG Opus](en.wikipedia.org/wiki/Opus_/(audio_format) at 75kbit/s — sounding the same to most people, but noticeable to an expert.