The octave buttons are used to shift the keyboard up or down in one octave increments. This extends the range of the keyboard in either direction, which lets you play notes that lie outside the number of keys available.
13. Has sustain button
A sustain button works in the same manner as a traditional sustain pedal. Pressing the sustain button and playing a note causes it to sustain. However, the sound will not stop until the button is pressed again.
8% have it
14. number of knobs
More knobs (rotating controls) can give the user more dedicated control over the device, eg. volume, effects, EQs etc. Types of knobs may differ: endless type or step type.
A type of knob that has a push button functionality built in. Encoders are for browsing and selecting your digital sound files or turning on a function that makes use of a control's rotation such as sound effects or tempo/tap tempo selection.
Devices can communicate in both directions with each other without any additional MIDI interface. The biggest advantage is that the USB connection can be used for everything; power supply, MIDI-in and MIDI-out. This means you need less cables.