The diatonic harmonica has a range of three octaves that are defined by the blow notes on holes 1, 4, 7, and 10. The range of an instrument is the number of notes that can be played on it, from the lowest note through the highest note the instrument can produce. An octave is defined by two notes with the same letter name that are 12 half steps apart, a half step being the smallest space between two notes in Western music. The higher octave note vibrates at twice the speed of the lower octave note, which is why the two notes sound the same. For example, the lowest C on the C diatonic harmonica, 1 blow, vibrates at 256 beats per minute (BPM) while the 4 blow C vibrates at 512 BPM.

FIGURE 2-4: Example of the three octaves of the harmonica

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