I am actually having issues with this as well. What I am doing is I am using a chromatic tuner on my phone. I sing the song in the same tune (or similar) to the actual singer.
You are about to leave Rhythm Gaming World and access the external songs DB. While no song or file sold for commercially available videogames is hosted there and only fan generated content is allowed, Rhythm Gaming World has no direct control over the database and no files are hosted here. Alright, we had to made you aware of this, now you can visit the database!
