The Midi specification allows 16 channels, each playing a different instrument. Each time you select a stop in Box Of Stops, it will assign that instrument to the next available channel, and start sending it notes.
Clearly for this to work the keyboard or synthesizer must be able to play more than one instrument at a time - it must be 'multi-timbral'. Most modern keyboards are - even if it's not obvious from the controls. In fact the specifications for [https://www.midi.org/specifications/item/general-midi General Midi] expect a keyboard to be multi-timbral. Please see [//boxofstops.com/howitworks-action this page] on the main website for a bit more detail on this topic.
== Adding a stop ==