Writing Alberti Bass
The Alberti bass is a specific broken chord pattern, whereby the notes in the triad are played in the order lowest-highest-middle-highest.
If you play the piano, you are probably already familiar with the Alberti bass pattern. It forms an accompaniment, usually in the left hand. It is used in many Classical era pieces, such as Mozart’s Piano Sonata in C, K545. This example is the opening of the 2nd Movement of the Sonata, but is also found in later styles.
In terms of chord analysis, the inversion of the chord is determined by the first, accented, note in each group (which is also the lowest note).
Notice that adjacent root position triads are acceptable. The potential consecutive 5ths are not problematic because breaking the chord makes them inaudible.
The first note in each group is also important because together, these notes build up into a bass line. The three latter notes in each group are normally played more softly, to help bring out the bass line. The bass notes will generally move by small intervals, typically not more than a 5th. (The prevailing key is Bb major in this example).
It is not untypical to have a substantial leap between the last note of one group and the first note of the next, and this is often a dissonant melodic interval such as a 7th or 9th. However, the sound is not dissonant, because the higher note is weak and the following note is more accented. As these notes are played by the thumb and little finger respectively, the stretch is not awkward despite the size of the interval.
Once a broken chord pattern is established at the beginning of a piece, the same pattern is then used throughout. This means that a piece which begins with an Alberti bass would not normally change to pattern with the notes ordered differently, such as any of the below:
The momentum within the pattern is brought to a stop at a cadence by using an unbroken chord. (Notice here the use of the triple appoggiatura (Eb, A, C), which is also very typical of the Classical style).
