Overblows and overdraws

Each hole of the diatonic harmonica is the opening to a chamber for two reeds, one that is activated by blowing, the other by drawing.

Anyone who has paid any attention to blues music has almost certainly heard harmonica players bend notes. A bend note is a note that is at least one half tone lower than the note of the same chamber and breath direction. On a harmonica in the key of C, the unbent draw note for chamber three is B, and the blow note is G. By drawing with a bend technique, you can drop the B to Bb, A, and Ab. The number of semi-tones, or steps you can bend, is determined by the interval between the draw and blow notes. Draw notes 1, 2, 3, 4, and 6 can all be bent. Blow notes 8, 9, and 10, can also be bent. Because of the way the harmonica is tuned, blow notes 7 through 10 are higher than the draw notes for the same chambers. For chambers 1 through 6 it is the draw notes that are higher in pitch.

The overblow technique forces a note that is higher in pitch than the one being played, how much higher depends, again, on the intervals. Blow note 6 – G on a C-harp – can be overblown three steps to produce a Bb note. Blow notes 1, 4, 5, and 6 can all be raised in pitch, or overblown. Draw notes 7, 9, and 10 can all be overdrawn.

What's interesting is that when a note is bent or overblown (or overdrawn), it is not the same reed that makes the note as when there is no change in pitch. There is a sympathetic response from the neighbouring reed in the same chamber. When you play the blow note 4 on a C harmonica, the blow reed vibrates and you play a "C". When you overblow this chamber, it is the draw reed that vibrates sympathetically while the blow reed is temporarily "choked" because of the way the air flows through the chamber.

The result is that, together with the bend notes, overblows and overdraws allow you to get three full chromatic scales from a humble 10-hole diatonic harmonica. It’s like doing something you were not supposed to do. Howard Levy, who spent a number of years playing harmonica and piano with Bela Fleck and the Flecktones, is generally credited for having innovated harmonica playing with the use of overblows and overdraws. Though by no means essential for serious blues harmonica (just listen to the recordings of Sonny Boy Williamson, Paul Butterfield, Little Walter, Junior Wells, and James Cotton among others), overblows and overdraws have become part of the technical repertoire of contemporary harmonica players.

overblows