What is the Dimi?
There are two types of harmonicas that are familiar to most people. One is the 10-hole diatonic harmonica, which is also known as the blues harp. The blues harp is played by a diverse range of musicians such as Little Walter, Bob Dylan, Charlie McCoy, John Popper, and Howard Levy. The second kind of well-known harmonica is the chromatic harmonica, which has been made famous by players such as Larry Adler, Toots Thielemans, and Stevie Wonder.
The "Dimi" is an altered form of the chromatic harmonica where the reeds are arranged in an alternate tone layout. An analogy might be that of a typewriter with an alternate keyboard layout that is an improvement on the traditional qwerty layout. The harmonica is a rare type of instrument in that you can change the pitch layout to suit your imagination with relative ease and relatively low expense.
The traditional chromatic harmonica is a difficult instrument, and benefits quite a bit from the change to the Dimi layout.
The Dimi is built upon two Diminished 7th chords a whole step apart. One blow, and one draw. Even more simply, the layout has a blow/draw whole step in each hole, with a half step interval between the draw of one hole and the blow of the next.
The Dimi has a slide, which raises each pitch a half step when pressed.