The correct effect works by comparing your input note with the currently specified correction scale to determine the final note to correct to.
For example, if the scale is C Major and you are singing closest to the D, your pitch will be corrected to the D based on the pitch correct parameters (like for example window and amount). The specified correction scale is octave independent meaning VoiceOne searches for the closest note in the scale relative to the octave you are singing in.
Using a MIDI scale allows you to specify the correction scale dynamically. You must HOLD a cluster of notes forming a scale, and while those notes are held, VoiceOne will use them to determine the octave independent notes to correct to.
If your window is too small and you hold down notes that are not in range, no correction will take place. If you only hold down a C for example, and your Window is 50 cents, correction will only occur when you are singing anything from a B to a C# in any octave. If you instead set the Window to 600 cents, your input will always correct to the closest C, regardless of what note you were singing.
We suggest that you start by setting Cor Attack and Cor Amount to 100% and Cor Window to 600 cents. This will ensure that pitch correction will definitely happen assuming the correct effect is enabled (the light on the correct button is ON), at least one MIDI note is being held down, and the VoiceOne is not in bypass mode. Once you have established that this setting is working, dial back the window, attack, and amount until you find a level of correction that suits your taste.
If you are trying to re-pitch a melody using MIDI notes (i.e. specify the exact note and octave to shift to), you should use MIDI shifting instead.