Richter tuning
Richter tuning is a layout plan for the notes of a diatonic instrument with multiple free reeds, such as a harmonica or accordion; the plan concerns which notes should be activated by each key (or hole). It is named after Joseph Richter, a Bohemian instrument maker who adopted the system for his harmonicas in the early 19th century, and who is also credited with inventing the mechanism that allows the harmonica to play different notes when the air is drawn instead of blown.
Richter tuning is designed as a compromise allowing players to produce both melodies and basic chords on diatonic instruments, despite their limited number of holes or keys. The lower portion of a Richter-tuned harmonica is designed to play the tonic and dominant chords on the blow and draw respectively (in the key of C, this would be the C major and G major chords). The remainder of the instrument is tuned to the notes of the diatonic scale (in this example, the C major scale), such that the blow notes are the members of the tonic chord (i.e. the first, third, and fifth notes of the scale), in sequence:
and the draw notes are those that are not members of the tonic chord (i.e. the second, fourth, sixth, and seventh notes of the scale), in sequence:
For example:
hole 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 blow note G C E G C E G C E G C E G C E G draw note B D G B D F A B D F A B D F A B
The above diagram shows that Richter tuning intentionally omits certain notes, particularly that the A and F are absent from the lowest octave (draw notes in holes 3 and 4). By comparison, solo tuning includes all the major scale notes (C D E F G A B C) for all octaves.