Stradella bass system

The Stradella Bass System (sometimes called standard bass) is a buttonboard layout equipped on the bass side of many accordions, which uses columns of buttons arranged in a circle of fifths; this places the principal major chords of a key (I, IV and V) in three adjacent columns. In a typical layout, as pictured, each column contains, in order:

The following chart shows a common 120-button Stradella layout.

Each bass note, and each pitch in a chord, is usually sounded simultaneously in multiple octaves. Larger accordions offer some control over the voicing with register switches.

In modern accordions, each chord button sounds three individual pitches. Early accordions sounded four pitches for the seventh and diminished chords. Modern Stradella systems omit the 5th from these two chords, allowing for more versatility. For example, an augmented seventh chord can be created by using the dominant seventh chord button and adding an augmented 5th from the right-hand manual or from one of the bass or counterbass buttons.

In most Russian layouts the diminished seventh chord row is moved by one button, so that the C diminished seventh chord is where the F diminished seventh chord would be in a standard Stradella layout; this is done in order to achieve a better reachability with the forefinger.

As the buttons are on the front face and cannot be seen by the player, an aid to navigation is provided by a small depression, hole or bump on the central C button in the root row, often supplemented by similar or different tactile marks on other selected root-bass buttons, such as the A♭ and E four buttons away in either direction.

When naming chord buttons, major chords are often suffixed with "M", for example "CM", to distinguish them from bass notes.

In staff notation, notes below the center of the bass-clef staff are bass notes, and notes above the center of the staff usually indicate chord buttons, labeled as necessary with "M", "m", "7", or "d" or "dim". (Repeated chords are usually only labeled on the first instance.)

Within this convention, the written octave for bass notes is arbitrary, as the Stradella system does not have buttons for higher and lower octaves.

An example:

As written:

As sounded, with one possible octave voicing:

Bass notes to be played on the major third (counterbass) row are indicated by repurposed "tenuto" lines below the notes (as in the E bass note in the example above), or underlined note names or numbers.

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