Editing Accordion (section)

====Left-hand keyboard systems====
[[File:120-button Stradella chart.svg|thumb|right|300px|Typical 120-button Stradella bass system. This is the left-hand keyboard system found on most unisonoric accordions today.]]
Different systems are also in use for the left-hand keyboard, which is normally used for playing the accompaniment. These usually use distinct bass buttons and often have buttons with concavities or studs to help the player navigate the layout despite not being able to see the buttons while playing. There are three general categories:
[[File:Bassmechanics.jpg|thumb|right|200px|The bass buttons trigger a complex mechanism of wires, rods, and levers, which is normally hidden inside the instrument.]]
* The [[Stradella bass system]], also called ''standard bass'',<ref>{{Cite web |title=Push Those Buttons! |url=https://accordionlifeacademy.com/articles/push-those-buttons |access-date=2024-08-16 |website=Accordion Life Academy |language=en}}</ref> is arranged in a [[circle of fifths]] and uses single buttons for bass notes and additional rows of single buttons for preset major, minor, dominant seventh, and diminished [[chord (music)|chords]]. The dominant seventh and diminished chords are three-note chord voicings that omit the fifths of the chords. 
* The Belgian bass system is a variation used in Belgian chromatic accordions. It is also arranged in a circle of fifths but in reverse order. This system has three rows of basses, three rows of chord buttons allowing easier fingering for playing melodies, combined chords, better use of fingers one and five, and more space between the buttons. This system was rarely used outside of its native Belgium.
* Various [[free-bass system]]s for greater access to playing melodies and complex [[bassline]]s on the left-hand keyboard and to forming one's own chords note-by-note. These are often chosen for playing [[jazz]] and [[classical music]]. Some models can convert between free-bass and Stradella bass; this is called ''converter bass''. The free-bass left hand notes are arranged chromatically in three rows with one additional duplicate row of buttons.
* Luttbeg double-keyboard piano accordions have a piano keyboard layout on both the treble and bass sides. This allows [[pianists]], most notably [[Duke Ellington]], to double up on the accordion without difficulty. The [[Bercandeon]] is an improved version of that instrument, also making it a "keyboard bandoneon".
* In 2021, a patent was published by Valerio Chiovarelli for a new bass system called the "Chiovarelli Jazz System".<ref>{{cite web | url=https://patents.google.com/patent/IT202100003890A1/en?q=(Chiovarelli)&q=G10D11%2f00 | title=Sezione dei bassi di una fisarmonica e fisarmonica comprendente tale sezione dei bassi }}</ref> This system is a variation of the Stradella bass system where, instead of triads, the chordal buttons of this system produce bichords (chords with only 2 pitches instead of 3).<ref>{{cite web | url=https://www.chiovarellijazzsystem.com/cjs/ | title=CJS &#124; Chiovarelli Jazz System }}</ref> The "Chiovarellia Jazz System" (or "CJS" for short) prioritizes the effectiveness of left hand accordion in jazz music, hence the name of the system, but according to the inventor, these chords can be useful when playing many varieties of music.