diatonic harmonica
A small free-reed instrument with ten holes, each producing two different notes (one on blow, one on draw), designed to play in a single key with bending techniques for chromatic notes.
In Depth
The diatonic harmonica (also called blues harp or ten-hole harmonica) is organized so that blowing and drawing (inhaling) through each hole produces different notes arranged to favor the tonic key's major scale. However, by adjusting the embouchure, tongue position, and airflow, players can "bend" notes — lowering their pitch by up to a semitone or more — giving access to blue notes and chromatic tones not built into the instrument's design. This bending technique is the foundation of blues harmonica style. The harmonica became a blues instrument through players like Sonny Terry, Little Walter (who pioneered amplified harmonica through a bullet microphone), and Sonny Boy Williamson. Little Walter's use of amplification and distortion essentially turned the harmonica into an electric instrument, creating tones rivaling the electric [guitar](/term/electric%20guitar). Bob Dylan made the harmonica a folk-rock symbol. In country, Charlie McCoy demonstrated extraordinary chromatic facility on the diatonic instrument. The harmonica remains one of the world's most popular instruments, with over 40 million sold annually.
Little Walter revolutionized blues harmonica by cupping a small microphone against the instrument and playing through a guitar amplifier — the distorted, overdriven sound he created influenced rock guitarists and remains the benchmark for amplified blues harp.