MIDIStatus

MIDIStatus is a term used to describe the status information of a MIDI data stream as indicated by the status byte of MIDI messages. The status byte determines how the following data bytes should be interpreted and which channel or system context applies. In typical MIDI streams, most messages are channel voice messages that carry data for a single channel, with status bytes ranging from 0x80 to 0xEF. Each status byte encodes a command (such as note on, note off, control change, program change, or pitch bend) and a channel number, while data bytes (0x00–0x7F) carry the associated parameters.

System and real-time messages form another class of MIDIStatus. System common messages use the 0xF0–0xF7 range, while real-time messages use 0xF8–0xFF and can be interleaved with other messages. A System Exclusive (SysEx) block begins with 0xF0 and ends with 0xF7, allowing devices to exchange manufacturer-specific data. Real-time messages such as 0xF8 (Timing Clock), 0xFA (Start), 0xFB (Continue), 0xFC (Stop), 0xFE (Active Sensing), and 0xFF (System Reset) are designed to be transmitted independently of the current channel voice status.

Running status is an important optimization related to MIDIStatus. When consecutive messages share the same status, the status byte can be omitted for subsequent messages, with only the data bytes following. This reduces bandwidth in streaming MIDI data streams.

In practice, MIDIStatus is a core concept used by software and hardware to parse, route, and synchronize MIDI data. Implementations typically maintain a currentStatus, track the expected data byte count, and properly handle running status alongside interleaved system and real-time messages. See also MIDI protocol, MIDI channels, and SysEx.