It is important to have your preview instruments set that are used for specific purposes. Any of these instruments can be a soundfont, or VSTi plug-in, or you can send MIDI messages to an external software or hardware synth. When using the latter, you need to choose “MIDI: General MIDI”.

Chord Preview Instrument

This is the instrument that is used the most, not just for chords but also for listening to phrases. Using a piano is recommended here, e.g. the included RCPiano soundfont.

Bass Preview Instrument

Used only when listening to chords together with bass notes (option: Chord+Bass). You can set a piano instrument here too.

Scale Preview Instrument

Used only when previewing scales, e.g. by right clicking on a scale in the Scales browser.

Rhythm Preview Instrument

Used only when previewing rhythm patterns. By default the RCClick soundfont is used for this purpose.