'Rules' for piano chords in the Chord Charts

Hi all, I was hoping you could help me understand the ‘rules’ for building piano chords in the chord charts.

I’m looking at the chord charts for the song ‘House of Gold’ by Twenty One Pilots, although I don’t think this is unique to this song. The first chord is ‘C’, and it’s played as I would expect - a low C, followed by C, E & G. But the next chord, the F, isn’t played F,F,A,C as I would expect, but F,C,F,A - and the A minor is A,C,E,A.

I guess these aren’t inversions, because the root note doesn’t move, and the changes do make it easier to play, but what’s the ‘rule’ here? How and when are chords changed? I’m wondering if I have a gap in my knowledge of how to play chord progressions on the piano!

Thanks in advance, Tony

  • The right-hand notes are extracted from the chord:
    • If the chord is a triad, the notes simply consist of all chord tones;
    • Otherwise, the chord must have 4 tones, e.g. from a seventh chord or an added ninth. In this case the bass is omitted from the right hand.
  • The notes are reduced to the number of semitones above C, assuming a default voice leading above Middle C.
  • Two actions may be repeated:
    • The highest note is lowered by an octave, i.e. the right hand inverts downwards.
    • The lowest note is raised by an octave, i.e. the right hand inverts upwards.
  • The final voice leading should be such that the average octave value of the notes is just greater than the value of the harmony track given in the mixer (which is also relative to Middle C), and no longer remains so if the right hand invert downwards.

The voicing is unique since there is exactly one voicing where the average octave of the notes is in the range (0, 1 ÷ number of notes].

The bass note is also handled similarly, except that there is only one note to change the octave of, the octave mixer value is relative to F3 (The Middle C is C5), and the MIDI value calculated from it rounds off before being compared to the bass note value. This could be simplified to a unique lowest note depending on the decimal part of the value:

+x.0 +x.1 +x.2 +x.3 +x.4 +x.5 +x.6 +x.7 +x.8 +x.9
-x.0 -x.9 -x.8 -x.7 -x.6 -x.5 -x.4 -x.3 -x.2 -x.1
   F   F#    G    A   A#    B    C   C#   D#    E

To illustrate how to determine the voicing in Hookpad, here are two examples:

  • G♯m/D♯, octave 0
    • The right hand consists of the notes G♯, B, and D♯.
    • These translate to 8, 11, 3 semitones above Middle C.
    • The notes are inverted downwards successively:
      • 8, 11, 3: average = 0.611
      • 8, -1, 3: average = 0.277
      • -4, -1, 3: average = -0.056
    • The second voicing above is the one that is just above the octave value of the harmony track.
    • Transposing by these steps from Middle C, the voicing is B4 - D♯5 - G♯5.
    • Following a similar procedure, the bass note found to be D♯4 if its octave value is also 0.
  • B7, octave 0.5
    • The right hand consists of the notes D♯, F♯, and A.
    • These translate to 3, 6, 9 semitones above Middle C.
    • The average octave value is equal to the mixer value, so the chord is inverted upwards once to obtain 15, 6, 9.
    • Transposing by these steps from Middle C, the voicing is F♯5 - A5 - D♯6.
    • The bass note found to be B3 if its octave value is also 0.5. Given the same value, A♯ would become A♯4 (similarly for B♭).