The left side of the Striso, or the bass side, uses an auditory illusion called pitch circularity to make it possible to play all notes with the same perceived pitch height. This is done by playing the note in three successive octaves and mixing them such that the perception of the pitch height changes.
Changing the perceived pitch height while playing is possible using the direction sensitive buttons.
This is especially useful for accompaniment, where it is most important which note or chord is played, and less so in what octave or inversion. Like a guitar player often doesn’t know the exact notes he plays, only which chords they form.
The main goal of having perceived pitch height modulation is to relieve the musician from the limited choice of octaves and inversions a chord can be played in, instead giving a continuous sound space. This gives more possibilities, and at the same time makes the choice easier, since any pitch height can be chosen with the same buttons.
Here some audio examples are presented of the perceived pitch height modulation method. These are generated examples and hence may sound a bit dead.
The first example is a major scale where the perceived pitch height is constant. You might hear jumps, but different ears can hear different jumps, as further explained in Diana Deutsch website linked to below.
The second example is the same scale, only the notes are played alternating with the base note.
In the third example the perceived pitch height goes the opposite direction of the pitch chroma: the scale goes up, but ends an octave lower than it started.
These are only a few examples to get an idea of the possibilities.
The method used here is called perceived pitched height modulation and is described in the NIME 2014 paper about the Striso.
More background information about pitch circularity and pitch perception is found at the website about auditory illusions by Diana Deutsch.