after youve downloaded, open audacity and click  Project>Import Audio and find the .mp3 and click open
then youll see a track with blue bars, next to that will be the name of the song. click it and click Split Stereo Track, if that isnt there then just click Mono. if it does say Split Stereo Track then click it and there will be two tracks now. click both names and press Mono, then click File>Export as Ogg Vorbis and save it to Blockland\base\data\sound\music and itll work in blockland