The most commonly used harmonica is the diatonic harmonica. It normally has a 10-hole design and is available in all 12 chromatic keys. Other names for the diatonic harmonica include the harp, short harp, blues harp and standard 10-hole. The design of the diatonic harmonica allows an individual to play the complete seven-note major scale in the key type of the harmonica. Inhaling or bending and exhaling or blowing allows for notes outside of the major scale. The diatonic harmonica is used in blues, folk, country and rock bands. It is the harmonica recommended for beginners.
The chromatic harmonica can be identified by the button at the end of the harmonica that is used to change the chromatic of the instrument. The button is used to hit the notes in-between the chosen major scale. The button also allows the harmonica to play in any key. Bending notes is very difficult. Classical and jazz music are the most common use for the chromatic harmonica.
The tremolo harmonica has a double row of holes that are diatonic. The tremolo harmonica is made with eight or more holes. There are two reeds in each hole tuned to the same note. One reed is tuned just a little higher. The tuning allows for a vibration or tremolo sound when either blowing or drawing. Bending the notes is not possible on a tremolo harmonica. The main use of the tremolo harmonica is special effects.
The octave tuned harmonica has two rows of eight or more holes. Both rows are diatonic. Double reeds are tuned within each hole. One reed is tuned an octave higher than the other. The sound produced is strong and full bodied. A good comparison of the sound is like a 12-string guitar.