I can't access some of the Melodyne controls on Mixcraft 10's sound tab

Go into Mixcraft's Display preferences and select the option called "Disable Per-monitor DPI Awareness," then click OK and restart Mixcraft. That should fix the problem. 

Note: this is happening when the Windows display scale setting is set to something other than 100%.  Mixcraft 10 itself scales up correctly with Windows, but some plugins don't scale up, including Melodyne.