Hello psychotic one and welcome to the forum.
There is nothing wrong or forbidden to stop you from creating your version of an existing song for your own enjoyment.
What you can not do is perform the song in public without paying a fee to whomever owns the copyright to a song.
Songs like "Twinkle, Twinkle Little Star" have no copyright owner, no one to collect a performance fee, so they are public domain and can be performed anytime, any place, by anybody. If you record your performance, upload a copy of your performance to the internet you can post a link to that performance in the forum.
Several forum users have purchased a copyright performance license so they have paid the fee to perform a song. Typically they will include the license information if they post a link to a copyrighted performance.
Not really what I was asking.
I am trying to learn an instrument and instead of just the click of a metronome, I would like to use backing tracks. Sure I could use the song I am trying to learn as a backing track but I am not able to play up to speed. I have tried those "slow down" amps and gizmos but for the most part it puts everything out of pitch.
What I am looking for is a way to take an existing song (public domain to get my skills up) and use them as backing tracks at different speeds (50%, 60%, 70% etc.) without the pitch changing.
Here is the problem of that idea: How am I able to make a backing track of a song or melody that I never heard before? If I did hear it before, then how do I know that I make is what I hear in my head without wasting a lot of time trying to make it sound right instead of learning the instrument?
So my question again is simple: Does BIAB have the ability to make a backing track of a public domain song from the melody?
Feel free to make one out of Twinkle Twinkle Little Star or Mary Had A Little Lamb so I am able to hear it if you think that would be easier than trying to answer my question.