It has one more row of buttons than the melodeon and its pitch is set a half a tone below or above the melodeon. It is also possible on the accordion to get two notes out of one button by maneuvering the bellows a certain way. This helps the player use less finger movement and allows for more expression when playing.
There are many types of accordions under the button family. The differences range from the keyboard structures, the tuning and the construction of the instruments. A well know variety is the Diatonic button accordion.
It comes with a melody sized keyboard and the keys are the notes of diatonic scales. This can be just one. The bass of the Diatonic button accordion almost always has the principal chords not excluding the root notes of those chords.
Diatonic button accordions are usually bisonoric. This means that for every button used there is two sounds that come out: one when the bellows condensed and the other when they are expanded.
It is possible to get varieties that are unisonoric, like the garmon, which plays the same note, no matter if the bellows are expanded or contracted. Other varieties are able to function both as bisonoric or unisonoric instruments.
Another notable button accordion is the chromatic. It has a melody sized keyboard with rows of buttons that are arranged chromatically according to pitch.
The bass of the keyboard is usually the Stradella system. This is a converter system or a free bass system. Under the chromatic button accordians you will find the Russian Bayan.
The chromatic button accordion is sometimes simply referred to as the chromatic accordion. This is not technically the correct term because other accordions, like the piano accordion are chromatic too.
The chromatic button accordion is a more popular accordion among performers because the treble keyboard of the instrument is more dense. This gives the player a wider range.
In various cultures today there has been a number of developments and adaptations made to the button accordions. In Russia for example you have such accords as the Saratovskaya, the Garmonica, the Livenka, the Bayan , the Garmon to name a few.
