What is a Pitch Shifter and what is it for?
The Pitch Shifter effect (and among them the Octaver), are effects that transpose (that is, move up or down) a note or notes within a predefined interval (distance between two notes).
An Octaver is a type of Pitch Shifter because it transposes the notes exactly in an interval of octaves (12 semitones). This type of effect creates rich layers of sound, fattening it up and making it more interesting. Many octavers are used when a bass is lacking, setting it one octave below, which is usually the range in which the electric bass sounds.
In general, Pitch Shifters can transpose any note up or down. Normally it is used to lower some tones and, in this way, fatten the sound of our guitar. This is very useful in harder styles like Metal, but you can also get very curious and experimental effects.