I'm wondering if the melody, when you play it above an octave and those notes then become 9ths,11ths,13ths does that then give a reason to use extended chords to harmonize them? Or is there no correlation to where you are in the octave when using extended chords?

  • Yes, melody tones can be chord notes or passing tones or anything else. But as you say they have to be above an octave to become part of extended chords, otherwise they the 9th is a 2nd, 11th is a 4th etc. or non chord tones. – Albrecht Hügli Apr 7 '19 at 16:21
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    The melody notes don't have to be part of the chord played underneath. If they were tunes would basically consist of arpeggios. There are passing notes, getting usually from one chord tone to another, but often they're not included in the chord, and even an octave higher, wouldn't necessarily be included in the chord name. – Tim Apr 7 '19 at 16:37

Within an interval the octave matters. Saying something is a minor 2nd tells you that the tones are a half step apart, and saying the same letters are a minor 9th tells you they're an octave and a half step apart.

But within a chord the octave location doesn't matter at all. C9 is the tones C-E-G-Bb-D, no matter which octave each tone is in. If that wasn't true we would need a different name for every possible voicing... what would you call it if D was the bass? C7 (add -2)???

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