Because it is possible to play in all keys on the chromatic harmonica, it is possible to play a lot of music which could not be played on a diatonic harmonica. Some music can be learned simply by listening to recordings and imitating what you hear. However, recordings only began in the 20th century and there is a whole world of great music written before the 20th century which is unavailable to you if you can’t read music.
Even where there are recordings, as music becomes more complex it is harder to learn by ear. If you can read music well, you can often learn a new piece of music in a very short time. This ability allows musicians to play easily with a new group they have never played with before by the use of "charts" which contain the melody and chord changes to songs. If you intend to play Jazz or Classical music, it is essential to develop your ability to read and understand music in all keys.
The first step in developing this ability is learning to read scales and simple tunes without the aid of inhale and exhale or hole number markings. Shown as follows is the notation for a C major scale in quarter notes. You can already play this without even thinking. Play through it watching the notation and say the name of each note to yourself as you play.
The next step is recognizing the notes in different octaves. Since the notes on the harmonica repeat in identical patterns over three octaves, you can easily play a scale by ear in any octave once you know it. the following example is the notation for the C major scale played over two octaves in eighth notes and then sixteenth notes (see Note Values). Don’t let the notation for the higher notes scare you. They are simply repeats of the lower notes an octave higher. Think the names of the notes as you go. Once you can do this with sixteenth notes, you are well on your way.