How to get single note melody out of any tunes: an idea

When I learned that there is a popular method of ear training called 'interval ear training,' I was rushed to play it, but didn't have much success. Then I got an idea from a specific source: 'GNU Solfege'.

The idea is:-

1. Get the first note right, that is, the absolute pitch. You can get it right by comparing with your modal singing voice. In male, you could sing Do-Re-Mi-Fa-Sol-La-Ti-Do, starting from G, so it would be - G A B C D E F# G. In female, it would be C D E F G A B C. As a matter of fact, I think it is harder for males to sing C D E F G A B C if you are not a singer.
2. Learn the melodic interval, both ascending and descending, for minor second, major second, minor third, major third, fourth, perfect fifth, minor sixth, major sixth, and probably some other intervals. Only consider the melodic type intervals. Don't really think too much about some interval such as major seventh. which is probably rare.
3. Get the interval right between each notes of your tune. It is best to simply forget the absolute pitch as it will interfere with getting the interval right, and bias your thinking towards the wrong note.
4. Check your notes with the major scale, chords, and modes.

I am still testing my idea, though, but I hope this will point the readers towards the success. GL!