Ok, maybe I missed something, but I cannot find someone who explain this clearly and in detail.
I know a bit of the japanese music system and I’m studying it right now, and to me it looks pretty similar in many ways to the western system, although the shamisen notation left me confused.
The 4th position is clearly five semitones away from the open string (a fourth), the 3rd is a minor third, so I guess positions are like the grade of the western diatonic scale. (am I right?)
At the moment I play it this way, but some pieces seem to not follow this rule.
I’m a beginner with the shamisen, but I play guitar, piano and violin so if you point me to some serious studies about japanese music system and shamisen theory I’d be happy!