If you already have license for Singing tutor 2.?.?.? (for example 18.104.22.168 or 22.214.171.124) you can update it to last version free of charge!
You can use both Singing Tutor Single and Duet with same licese!
Previous lastest version of Singing Tutor 2.0 now available SingingTutor.v.126.96.36.199 Single (In this version implemented only single user mode)
Previous version of Singing Tutor 1.1 now selling as Singing Tutor-Basic 1.2 you can verify updates here.