One of the most commonly used alternate tunings is that of Open D. The tuning is used across many different styles of guitar music but most commonly it is used in blues and folk music. How to tune to Open D Open D tuning tunes the strings of the guitar so that when all the strings are played open it forms a D Major chord. The D Major chord is formed from the three notes which make up the D Major triad, these are the 1st, 3rd and 5th notes of the D Major scale, which are D, F# and A respectively. Thus, each of the guitar strings in open D tuning will be tuned to one of these three notes.