Investigate improved pitch shift quality

[gth828r]

I saw a comment on stackoverflow that someone recommended trying pyrubberband over librosa to improve pitch shift sound quality. In particular, librosa's output often has a tinny or metalic sound. From what I read, this is inherent to the algorithm that both of these libraries use, but pyrubberband may have better performance.

We should at least try it out and see if it is better. We can also investigate if there are any other alternatives. The current quality is not so bad that this is a big problem for such a silly project.