Layout:

Specifications:

• 7 Octaves + 2 Notes
• 120 keys : 86 Notes -> 1.4 Keys : 1 Note

The layout pattern loops - the bottom rows are repeated at the top of the next column along. For example, the F# and G at the bottom of column 2 are repeated at the top of column 3.

Chords:

With the chord keys being adjacent, it should be possible to two keys with the same finger.  Entire length of of chord might be playable with just four fingers.

Octave map:

Midi note values:

Midi value for each key could either be calculated on the fly or stored in an array.

After comparing all the isomorphic keyboards, I chose the Tonnetz layout because:

• Compact
• Low key to note ratio - reduces weight
• Chord shapes seem reasonable - compact and requires fewer fingers
• Full 7 octaves