Is there any technical reason why there is not a 64-bit build of Sonic Visualiser for Windows?
The main current reason is that there aren't any 64-bit builds of the various available Vamp plugins, and a 64-bit version can't load 32-bit plugins. Also, of the three supported platforms, Windows has done the best job of maintaining 32-bit compatibility. I do want to start doing 64-bit builds one way or another though.
Well, that's just a matter of getting in touch with the developers and ask them to provide 64-bit builds of their plugins. Or is it not that simple?
Windows is already a fiddly platform for many developers to build for (which compiler? which runtime? etc) and 64-bit builds are objectively fiddlier still.
Given that Windows does such a good job of running 32-bit applications seamlessly, and that Sonic Visualiser itself has enough extra dependencies to make maintaining both 32- and 64-bit builds a bit of extra work, so far it's seemed a reasonable tradeoff to stick with 32-bit on Windows. Actually, I've been rather grateful that the Windows platform architecture has been kind enough to support this -- the forced-march you get on the Mac is tough to handle but there you have no choice.
Still, now that all new Windows distributions are 64-bit, obviously it's about time we did catch up.