One of the features of Nuendo / Cubase is that you can process a clip or section of audio off-line with either a plug-in or built-in process. This off-line processing is non-destructive (you can undo it at any time) and allows for some very fast and flexible editing techniques.

Using the range tool select the piece of audio that you wish you tune. Use the command "Split Range" to extract the selected range into a separate event.

Right-click and choose to process the audio with Autotune - this will pop up Autotune’s GUI. Make sure you are using Autotune in graphical mode rather than automatic mode.

Press Autotune’s "Tracking" button (making sure "Internal" clock mode is also engaged) and preview your audio event. You will need to preview the full clip to ensure everything is correctly tracked. Once tracking is completed, disable the "Tracking" button and draw your tuning correction curves.

I like to use the line tool with snap to note enabled and smooth out the obvious tuning issues. You can preview the changes by activating the preview button again.

When you’re happy with the result press "Process" and Nuendo / Cubase will apply the changes/corrections to the audio event.

This is a very fast way to go through a track and select the out of tune parts and tune them whilst leaving the rest of the performance untouched.