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 below 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 recognising the notes in different octaves. Here is the C major scale played over two octaves in eighth notes and then sixteenth notes. Don’t let the notation for the higher notes scare you. They are simply repeats of the lower notes an octave higher. On the recording the harmonica has been omitted when the example repeats. Play along with the drumbeat while reading the notation. Think the names of the notes as you go. Once you can do this with sixteenth notes, you are well on your way.
Once you can recognise the notes from the notation, the best way to develop your reading is by doing lots of it! The most enjoyable way to do this is to read melodies. Here are some to practice. Read each one until you can play it from memory and then close your eyes and concentrate on playing with feeling and a beautiful tone.
The following melody is written in Cut Common time. The melodies are only a few examples. It is recommended that you purchase a book of song melodies and start learning the ones in C major. By the end of this book, you will understand how to read melodies in all the other keys as well. It is also a good idea to work your way through method books for other wind instruments, particularly Flute books, as the lowest note on the flute is middle C – the same as the lowest note on a C Chromatic harmonica.