You can spot a Tremolo harmonica almost immediately by its two rows of holes. But do beware, other members of the harmonica family, such as the Octave harmonic, also have two holes. It’s the special sound the Tremolo makes, which gives it its name and its unique place in the harmonica family.
Unlike a regular diatonic harmonica which has one reed for each blow and each draw note, the tremolo has two. The reeds in each pair are identical in size and appearance, however they are tuned very slightly apart fom each other. When the reeds sing, this difference creates a warm wavering quality to the note. The end effect is a jolly sound which is ideal for playing folk music.
The tremolo harmonica is ideally suited to folk and Scottish country music, as its sound is similar to an accordion. In Scotland this type of harmonica is know as a moothie. Hohner produce a specially tuned moothie called the Highlander, which can also sound very similar to the bagpipes because of the way its reeds are tuned. Here’s expert moothie player Donald Black, playing and talking about the Highlander tremolo harmonica.