The diatonic harmonica was designed to be played in just one key, making for more predictable, uniform melodies. As with all harmonicas, the diatonic versions are made with two plates of reeds which are cut with slots that the musician blows into to create vibrations. The combination of the vibrating reeds and the air stream provided by the harmonica player creates this instrument's distinctive sound.
Since the 1920s when the first known harmonica recordings were produced in the United States, the instrument has been used in a variety of music styles from folk to rock and roll and even rap. The diatonic harmonica was widely used during the 1950s by American blues musicians, who found new ways to play the "blues harp" to create a distinctive sound.
During the 1960s and 70s the diatonic harmonica was less prevalent as the guitar and electric guitar began to take its place during musical solos. Yet prominent musicians of the era such as Bob Dylan and Van Morrison continued to use this long-cherished instrument to create a more bluesy element in their folk and rock songs.
In more recent decades, musicians have been increasingly influenced by electric guitars in their use of the diatonic harmonica. During solos, some musicians now play the harmonica at a rapid pace, connecting the electric guitar to the harmonica to create a striking new effect.
Depending on the world region, the diatonic harmonica is known by different names and comes in slightly different forms. In East Asian countries including China, Japan, and Korea, a diatonic harmonica is called a tremolo, which signifies different volume changes. In Western countries, the tremolo harmonica is played mainly in folk music to add a wistful, blues-like sound.
In Europe and North America, a highly recognized type of diatonic harmonica also known as the blues harp is used. This instrument has ten holes that can produce 19 different notes.
The tremolo harmonica is unique in that it has two reeds for each note rather than one reed per note as in standard harmonicas. Players of this type of harmonica use the "tremolo" (which means an occasional shift in volume from quite to loud) to create a distinct wavering melody. This effect is achieved by using beats, or by repeatedly playing a single note.
The blues harp is perhaps the most well-known form of diatonic harmonica, and is a Richter-tuned, 10-hole instrument. These 10 holes produce 19 different notes across three octaves, and one major full scale is available. This harmonica is played mainly in blues, American folk music, and rock and roll.
One can identify the diatonic harmonica by taking a closer look at its features. For example, the Richter-tuned blues harp has a layout of 12 keys, thus 12 slots on its side.
The tremolo diatonic harmonica is generally a flatter instrument, which has 21 to 24 holes on its side, double that of the standard version. These slots are generally either placed in two rows of 12 or one long row of 21. Many newer models of the tremolo can be identified with four different-colored slots placed every five holes along the length of the instrument.