This isn't directly a Linux topic, but many users on this list have experience with pipe organs.  A friend of mine forwarded me this piece:

https://www.youtube.com/watch?v=ii3l44_xD2s

The stop in question, the Vox Humana, can be heard at 1:27.  Apparently, it's unique.  Can anyone please tell me a little about how this one works?  i hear a very early formant filter and am wondering just how this might be mechanically accomplished.

Thanks!

Tom