I have finally managed to get together all the bits that go into a release of the Rubber Band library, and so have just released version 1.8.2.
The Rubber Band library is a software library for time-stretching and pitch-shifting of audio, particularly music audio. That means that it takes a recording of music and adjusts it so that it plays at a different speed or at a different pitch, and if desired, it can do that by changing the speed and pitch “live” as the music plays. This is impossible to do perfectly: essentially you are asking software to recreate what the music would have sounded like if the same musicians had played it faster, slower, or in a different key, and there just isn’t enough information in a recording to do that. It changes the sound and is absolutely not a reversible transformation. But Rubber Band does a pretty nice job. For anyone interested, I wrote a page (here) with a technical summary of how it does it.
I originally wrote this library between 2005 and 2007, with a v1.0 release at the end of 2007. My aim was to provide a useful tool for open source GPL-licensed audio applications on Linux, like Ardour or Rosegarden, with a commercial license as an afterthought. As so often happens, I seriously underestimated the work involved in getting the library from “working” (a few weeks of evening and weekend coding) to ready to use in production applications (two years).
It has now been almost six years since the last Rubber Band release, and since this one is just a bugfix release, we can say the library is pretty much finished. I would love to have the time and mental capacity for a version 2: there are many many things I would now do differently. (Sadly, the first thing is that I wouldn’t rely on my own ears for basic testing any more—in the intervening decade my hearing has deteriorated a lot and it amazes me to think that I used to accept it as somehow authoritative.)
In spite of all the things I would change, I think this latest release of version 1 is pretty good. It’s not the state-of-the-art, but it is very effective, and is in use right now in professional audio applications across the globe. I hope it can be useful to you somehow.