What are the buttons for?
Unless the instrument is a piano-accordion, there will be buttons on the right hand side.
These are single pitches for playing a melody. If two or more are sounded, of course, a chord results. The arrangement varies from instrument to instrument, but may be similar to this configuration.
The left hand also has buttons. This is true whether it is a button box or a piano-accordion. The simplest arrangement may be the 12-bass accordion. One row of buttons will provide a single pitch as named below, while the second (lower) row will provide a major chord based on the same pitch.
In staff notation, these sounds would look like this:
An accordion that has more bass buttons simply expands this arrangement to include additional pitches and chords. In addition to a bass and major chord, it is possible to play an additional bass (upper row) related to the major chord (counter-bass) as well as the minor, seventh and diminished chords associated with each bass in the second row. The 120-bass accordion, which is industry standard, has this arrangement:
IThe 12-bass arrangement can be seen in the middle of this configuration, thus showing how the 120-bass expands on the basic scheme. (This is true for 32-bass and 48-bass accordions as well). The additional pitches provide all the tones that are needed to play in any tonality. The C-line and the F-line, for example, provide these sounds, as seen in staff notation:
This arrangement of buttons to play bass and chords allows the accordion to accompany songs in any major or minor tonality, much like the circle of fifths which reflect all tonalities.
The bass arrangement is known as a Stradella bass. Some accordions use a free-bass system, however, which means each left-hand button is a single pitch. Chords are then created by combining these buttons, much like the right hand.