Compound Chords & Extensions
Yeah, more boring music theory... 
I've been meaning to do some brain dumps of some of the concepts I learned in music theory decades ago for some time now, but just haven't gotten around to it. But, I've gotten a few PMs and questions about the chords in some of my recent tracks over the past few months, so I figured I'd take a moment to try to get a discussion going and, hopefully, trigger some new considerations for all our benefit.
Whether you’ve realized it or not, most of us have probably used compound chords, which are simply playing two chords simultaneously. Some people think of them as simply “extensions” (i.e., adding additional notes, usually in thirds, to a triad to create 7th, 9th, 11th, etc. chords), but they can also be thought of as two separate chords layered together. Example:
Cmaj9 = C E G B D
Or, you can think of this chord as a Cmaj (C E G) and Gmaj (G B D) played together (with the 5th note [G] of the root triad shared between chords). More examples in the parallel (Cmin) and relative (Amin) minors:
Cmin9 = C Eb G Bb D (or Cmin [C Eb G] and Gmin [G Bb D] chords played together)
Amin9 = A C E G B (or Amin [A C E] and Emin [E G B] chords played together)
Now, these are relatively simple compound chords and they all share a common note (i.e., the fifth of the root triad). And, these are also used fairly commonly in trance and house music. But, compound chords are usually thought of as layering two completely different chords (i.e., no overlapping notes) together, as in 11th and 13th chords:
Amin11 = A C E G B D
This is essentially an Amin chord (A C E) with a Gmaj (G B D) chord played over it.
Cmaj13 = C E G B D F A
This can be thought of as a Cmaj (C E G) with Bhalf-dim7 (B D F A) played over it. Try it!
As mentioned above, compound chords are often not necessarily defined as extensions; for example, try playing a second inversion of a Dmin chord over a Cmaj:
C E G A D F
That’s a pretty pleasant sounding chord, but make that a Dmaj over a Cmaj and you’ll get some dissonance, which can also sound great in the right context:
C E G A D F#
These more complex chords are less common in EDM, and probably used more in house than in trance, but try some of them and see.
So, why are these useful? Well, many reasons actually. One reason they’re useful, particularly in EDM, is that you can build beautiful lush chord progressions using these types of chords. It seems like a lot of people ask how to make their pads sound as lush as the pros do, thinking that it is all a matter of synthesis and layering of sounds, when in reality, it’s often a combination of the layered sounds AND the layered notes. Compound and extended chords add a lot of lushness to your sound that you won’t get from playing simple triads. Another reason they’re useful is that they give you more options for melodies, as well as a different context for them by providing more underlying notes from which to build your melody. And, yet another reason they’re good is that you can vary your chord progression by using different variations of root (i.e., bass) notes under the same chords – for example, you can add a whole new context to a chord progression that starts with a Bmin11 (B D F# A C# E; bass = B), by using an A in the bass note under the same chord to create a different context (essentially a Bmin played over an Amaj), etc.
One last consideration for now is voicing (relative arrangement of where the notes are played). Generally speaking, it’s a good idea to spread the notes of these chords across the range and try to keep notes that only a ½-step or full-step interval apart in different parts of the range, and typically in the higher ranges, to avoid too much dissonance. For example, if your chord is the Cmaj9 mentioned above, which has both a C and a B in it (i.e., a semitone apart) it’s a good idea to play the B in the higher register and in a different octave than the C (as opposed to directly adjacent) to avoid too much clashing. That is, unless you actually want that dissonance (it is desirable sometimes). Another consideration is that you don’t have to have just one sound playing all the notes in these chords – you can have one sound playing some notes, another sound playing others, the melody part adding more, etc.
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Last edited by cryophonik on Jul-15-2010 at 18:51
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