In case you don't know about this App, it provides a wonderful way to practice Jazz tunes. You can download it to an iPhone. It's not free- it costs about $13, but is well worth it. I have used it for years. For anyone here who is working on Jazz tunes, this is the way to go. Of course backing tracks played by humans will always feel better, but this app gives you a lot of flexibility for changing chords, changing the feel, key, tempo, etc. It's become an invaluable tool for me and I highly recommend it.