Guiding style harmony in the Accompaniment Machine

When performing a piece using styles on a keyboard, the function of the left hand is to signal the harmony applied to the style notes. The required information is 1) the chord root note and 2) the chord type. The easy-chord (or two-finger) system for Yamaha keyboards makes it relatively simple to lead styles harmonically. When accompaniment is active, pressing a single key in the bass region of the keyboard (below the split point) shifts the notes of the style so that they correspond to the major chord of the key. For example, you press any G key if you need GMaj. Other chords are formed by simultaneously pressing addition keys below the root. The following rules apply:

  • Press the root key and the next lowest white key to define a 7 (seventh) chord.
  • Press the root key and the next lowest black key for a min (minor) chord.
  • Press the root key and both the next lowest white and black keys for min7 (minor seventh) chord.

The richness of styles often compensates for the limited chord set. The four chords (analogous to the bass key rows on an accordion) are usually sufficient make good renditions of songs. You can include other chords by pressing the actual notes of the chord. (In this case, the root note is at the bottom). Yamaha keyboards recognize about 30 chord types. Implementing this option is well within the capability of a professional jazz pianist, but is quite challenging for an amateur musician. You would need to memorize 330 key combinations (11 root notes, 30 chords).

Although KBDI-Infinity supports the full Yamaha easy-chord system, we have introduced an option that is better suited to average performer. It features a rich set of chords that can be invoked with simple key combinations. About 10 chord types can be represented by a set of 1, 2 or 3 finger combinations that are easy to play and to remember. Certainly, the Maj, 7, min and min7 chords should be included. To decide on the other seven chords, we analyzed a large set of randomly-selected songs in The Best Fakebook Ever, 4th Edition (Hal Leonard Corporation). We marked an instance each time an alternate chord appeared in a song. Some chords almost never appeared, and others were prominent. With the following chords included, it possible to make an exact chord match over 95% of the time: Maj7, dim, dim7, Maj6, Maj9, min6 and 7#5 (or 7aug in the Yamaha chord notation). The set provides enough variety of make good substitutions for infrequently-encountered chords.

Our goal was to maintain the strategy of the Yamaha system so ours would be easy to learn. On the other hand, the Yamaha method of referencing chords to adjacent black and white keys is confusing because the pattern depends on the root note and often leads to awkward finger positions. We picked the MIDI note step (a difference of 1 in the GM note number) as the basis for our sysem. For example, B is one step below C and Bb is two steps. The table below shows the KBDI fingering conventions. Depressing a single key (the root) gives a major chord. pressing the root key and the adjacent lower one (-1 step) gives a 7 chord (e.g., B-C for C7). Similarly, pressing the root key and the next lower one (-2 steps) gives a minor chord (e.g., Bb-C for Cmin). We limited the maximum step interval to 6 to ensure that all chords could be played in the space below the split point of a 61-key keyboard.

KBDI Fingering System
Chord No Fingering Chord Notes
0 Root Maj C-E-G
1 Root-1 7 C-E-G-Bb
2 Root-2 min C-Eb-G
3 Root-3 min7 C-Eb-G-Bb
4 Root-4 Maj7 C-E-G-B
5 Root-5 dim C-Eb-Gb
6 Root-6 dim7 C-Eb-Gb-A
7 Root-1-2 Maj6 C-E-G-A
8 Root-1-3 Maj9 C-D-E-G-Bb
9 Root-1-4 min6 C-Eb-G-A
10 Root-1-5 7aug(7#5) C-E-G#-Bb

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[4] Download the KBD-Infinity Instruction Manual: kbd-infinity.pdf.

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