I like playing along with songs as they are, but I'd like to find some backing tracks with drums and guitar but not vocals or bass - ideas? Karaoke tracks? Software?
You can find a lot of multitrack files online, taken from games like Guitar Hero, where you can change up the mixing of the different tracks. You can use Audacity (or Garage Band, or other programs) to then adjust the levels for the different parts of the track. It's easy enough to mute out the bass, but if you also have a guitarist you are playing with you can cut the lead guitar as well, leaving drums, rhythm guitar and vocals. The guitarist leaves, and you can bring that part of the track back in.
