The System MIDI channel (CH) is used for the following scenarios:
- Using an external MIDI keyboard in place of the K-25m. This allows you to play several parts with their settings, such as Key Range, using the connected MIDI keyboard. This won't be possible if you play CH.A or CH.B individually.
- When a pattern is selected, a corresponding program change command is sent via this MIDI channel. Vice versa, program change messages can also be sent to the JD-08 via this MIDI channel to select patterns using an external MIDI device.
For more information, please refer to the MIDI implementation in the JD-08 Reference Manual.