Capo's and Keys

An 13th chord is a chord with the 13th note from the scale added. The 13th note is a B, which is also the 6th note (The numbers wrap-around, so the 9th note is the same as the 2nd etc.). We call that chord D13 instead of D6 to tell people that it has all the extra notes up to the 13th included. You take a basic D7, add a 9th, 11th and 13th note. (We ignore the 8th, 10th and 12th notes of the scale because they're the same as the root, 3rd and 5th, which are already included in the basic chord that you're extending.)

Of course in practice you'll have to skip some notes as you can't play 7 notes at once on a 6-string guitar, but that's the theory :)

I don't seem to be doing too well at explaining things today :roll:, but as always, there's a very good article that explains better than I can right here on GN, find it here.

for beiing difficult, the D major 13 isn't in fact a chord from that key, because the scale from that key exists only of a selection of 7 notes as the article of dhodge quoted.

@ misanthrope, the tool helped a lot at understeanding that each scale note has it's own chords.

for beiing difficult, the D major 13 isn't in fact a chord from that key, because the scale from that key exists only of a selection of 7 notes as the article of dhodge quoted.

D major 13 does indeed belong to the key. As that long list I wrote out for you shows, D maj13 contains ALL of those 7 scale notes:
D F# A C# E G & B - which is just the D major scale rearranged.

I've made a sheme for better understanding for me. Example : put the capo on 2nd fret, everyting moves up 2 tones, inlcuding the base notes of the traids, if I am right ? It is strange that when you play 4 notes of D major is the same as the 5 notes when you play the C major with the capo on the 2nd fret. Who can explain that ?

The open D major chord:

e|----2----
B|----3----
G|----2----
D|----0----
A|----x----
E|----x----

has 4 notes as you say, D, A, D and F#. These are the 1,5,1 (or 8) and 3 of the D major scale.

The open C major chord:

e|----0----
B|----1----
G|----0----
D|----2----
A|----3----
E|----x----

has 5 notes, C (1), E (3), G(5), C (8) and E (3).

With a capo on the 2nd fret, these are raised by a wholetone to D,F#,A,D,F#.

I hope this helps.

You've got an extra F# there, thus it's not the same as the open D chord. Still it sounds the same, for me...