Is there a plugin can fixs pitch of singers under Linux?

[mokapot]

You can use waves plugins with Carla, or at least try to. I'm not sure about the waves vocal tuning plugin yet, got to try it later...
I had to install some packages to get Carla working with windows plugins, I don't remember why but I ended up installing both 32bit and 64bit VST support for Carla. I have only experimented with the 7 day trial versions of some plugins such as the SSL channel strip, just to compare it to mixbus. I didn't feel like my set of plugins in MB was missing anything so I havent tried if you can get those windows plugins working through Carla INSIDE MIXBUS. (The Carla host appeared in my plugin list in MB3) I heard some people have got melodyne working in linux too. So if you don't mind using windows plugins... You could try to get Carla working with them.

[Jostein]

I can confirm that the Zita AT-1 is good and I have used it for two or three years now. It seems to me that Arch Linux do not have a package for AT-1, but Arch do have a system for using deb repositories, so if you download the KXstudio version of AT-1, then you are golden.

If I understand it right, then Melodyne (32 bit) might work under Wine. I tested it in my 64-bit system and it doesn't work there.