Nick - ok.. here's a crash course in aug6 chords... the aug6 chords are a family of chords that first appeared in the 17th century, but which became far more popular in the 19th century..
when working them out it does not matter if the key you are in is minor of major, the same basic rules apply..
an aug6 chord is generally thought of as an alternative to chord IV and is always in first inversion.
the chord following and aug6 is always either V or I 64 [chord I - 2nd inv]..
the oldest and most basic aug6 is called the Italian 6th [It6] and is a triad spelt [with respect to the tonic of the key]:
root = #IV, 3rd = bVI, 5th = I [diatonic]
so in the key of C [or Cm]
root = F#, 3rd = Ab, 5th = C
throw the chord into 1st inv and you'll see that the Ab is now the base note.
looking from the lowest sounding note [3rd], you'll see that the interval to the root is an augmented 6th [which you'll note has the same temperament as a minor 7th]
next comes the French 6th [Fr6]
this is that same as an It6 but with the inclusion of an augmented 4th with respect to the bass note... to determine the impact of this by stacking the notes in succesive intervals of 3rds, and considering that the lowest sound note of the aug6 chord must always be the bVI degree [in our case = Ab]
- the chord can now be re-understood as a 'modified' II7 64 [chord II7 in 2nd inv]
the French 6 [Fr6] is a 7th chord and is spelt [with respect to the tonic of the key]:
root = II, 3rd = aug IV, 5th = minor VI, 7th = I
so in the key of C [or Cm]
root = D, 3rd = F#, 5th = Ab, 7th = C
the Fr6 is in 2nd inv so the lowest sounding note is Ab.
Next comes the German 6th [Ge6]
this is that same as an It6 but with the inclusion of a perfect 5th with respect to the bass note... to determine the impact of this by stacking the notes in succesive intervals of 3rds, you'll see that the Ge6 is an It6 + a diminished 7th.
the German 6 [Ge6] is a 7th chord and is spelt [with respect to the tonic of the key]:
root = #IV, 3rd = bVI, 5th = I [diatonic], 7th = bIII
so in the key of C [or Cm]
root = F#, 3rd = Ab, 5th = C, 7th = Eb
the Ge6 is in 1st inv so the lowest sounding note is Ab.
If you take a closer look at the Ge6 chord you'll notice that it has the same temperament as a dominant 7 chord roots on the minor VI of a scale - and this is why it is so usefull for modulating to distant keys.....
There is another odd aug6 called "the Tristan chord" or the "Tristan 6th" [Tr6] after the Opera Tristan Und Isolde by Wagner.. everytime Tristan shows up this odd chord sounds.. if I recall correctly it's something like a modified Fr6 where the interval from the 5th to the 7th is a minor 3rd instead of a major 3rd]..
however the resolution rules of aug6 to V or aug6 to I 64 remain true..
Tr6 in C = D, F#, Ab, Cb where the lowest sounding note is Ab...
a chord in the key of C where the tonic has had an enharmonic shift ! ! ! - spooky..
Note: the above information is most likely not too far from the truth.. I am sitting at work at my desk writing this [instead of doing the 'day job'] completely from memory and without the aid of reference documentation to remind me of how stupid I am.. if I've goofed up the math.. I'm sure some clever bastard will gladly put me right.. lol..
