Okay I just unlocked this in about a 3 hour time period. There are 21 songs. Now I prefer guitar, but i'm not that good for sin wagon so I tried vocals. I CANNOT SING and I managed to beat the game on expert this way anyway. You can humm, make up your own words, or sing along as long as you sing it in the correct tone, it will count. This can only be done in single player. It is a lot easier to listen to the songs first so you know how to sing it. There are a few tricky ones closer to the end and the girls voice songs killed me lol but I managed to do it and so can you.