MIDI Machine Control


MIDI Machine Control, or MMC, a subset of the MIDI specification, provides specific commands for controlling recording equipment such as multi-track recorders. MMC messages can be sent along a standard MIDI cable for remote control of such functions as Play, Fast Forward, Rewind, Stop, Pause, and Record. These are "System Exclusive" messages, specifically Real Time Universal SysEx messages.

MIDI Universal Real Time SysEx Message Format

MIDI includes System Exclusive messages that are extensions of the MIDI format implemented by MIDI manufacturers. Some of the extensions, the "Universal" ones, are a set of the same functions that different manufacturers can implement differently in detail. Some of them are Non Real Time, with no reliable delivery timing. Others are Real Time, including MMC, so they are more reliably delivered when expected. SysEx messages start with F0 and end with F7. Universal Real Time SysEx messages start with F0, followed by 7F, then include other fields before the terminating F7.
The following shows Universal Real Time SysEx message format :
where Device-ID is:
and Sub-ID#1: is one of the following values. The bolded values are MIDI Machine Control related:
01 = Long Form MTC
02 = MIDI Show Control
03 = Notation Information
04 = Device Control
05 = Real Time MTC Cueing
06 = MIDI Machine Control Command
07 = MIDI Machine Control Response
08 = Single Note Retune

MMC Message Format

An MMC message is either an MMC command or an MMC response. As a SysEx message it is formatted :

Sub-ID#1: 06 = command
 Sub-ID#2:
 01 Stop
 02 Play
 03 Deferred Play 
 04 Fast Forward
 05 Rewind
 06 Record Strobe 
 07 Record Exit 
 08 Record Pause
 09 Pause 
 0A Eject 
 0B Chase
 0D MMC Reset 
 40 Write 
 parameters:  4F  <track-bitmap-bytes>
 44 Goto 
 parameters: =06 01     
 47 Shuttle
 parameters: =03    


Sub-ID#1: 07 = response
 Sub-ID#2: response state
 parameters: values detailing response state

MMC Commands

MMC Commands are either MMC transport messages containing one byte representing the command, or other types containing the command byte followed by parameter bytes. Some parameters are lengths of collections of bytes in the message, some parameters are constants associated with the command, other parameters are variable data values specifying command execution.

Record Ready

The Record Ready message will record-enable tracks. It is formatted :

F0 7F  06 40  4F  <track-bitmap> F7


length1: number of bytes between length1 and F7
length2: number of bytes in the track bitmap
track-bitmap: Each track is assigned a bit in the track bitmap.

To set a track, you must know both the byte in which the track's bit lives, and also the bit corresponding to that track. Note that each byte can only hold 7 tracks.

Track 1: byte 1 + 0x20
Track 2: byte 1 + 0x40
Track 3: byte 2 + 0x01
Track 4: byte 2 + 0x02
Track 5: byte 2 + 0x04
Track 6: byte 2 + 0x08
Track 7: byte 2 + 0x10
Track 8: byte 2 + 0x20
Track 9: byte 2 + 0x40
Track 10: byte 3 + 0x01
and so on.

Goto/Locate

The Goto message cues recording or playback to an SMPTE time. It is formatted :

F0 7F  06 44 =06 01 
     F7


Sub-ID#2 =44: LOCATE command
length: 06 Data byte count 
subcommand: 01 TARGET
hr: hours and type ; values 0-17 
mn: minutes; values 0-3B 
sc: seconds; values 0-3B 
fr: frames; values 0-1D 
ff: sub-frames / fractional frames ; values 0-63

Shuttle

Both forward and backward shuttling share the same MMC message; direction is encoded as a sign value. It is formatted :

F0 7F  06 47     F7
Note: sh, sm and sl are defined as Standard Speed in the MIDI 1.0 Recommended Practice RP-013.
sh = Nominal Integer part of speed value: 0 g sss ppp
 g = sign 
 sss = shift left count 
 ppp = most significant bits of integer multiple of play-speed
sm = MSB of nominal fractional part of speed value: 0 qqqqqqq
sl = LSB of nominal fractional part of speed value: 0 rrrrrrr
Speed values per shift left count:
BINARY REPRESENTATION USABLE RANGES 
Integer multiple Fractional part Integer Fractional
sss of play speed of play speed range resolution
000 ppp - qqqqqqqrrrrrrr 0-7 1/16384
001 pppq - qqqqqqrrrrrrr 0-15 1/8192
010 pppqq - qqqqqrrrrrrr 0-31 1/4096
011 pppqqq - qqqqrrrrrrr 0-63 1/2048
100 pppqqqq - qqqrrrrrrr 0-127 1/1024
101 pppqqqqq - qqrrrrrrr 0-255 1/512
110 pppqqqqqq - qrrrrrrr 0-511 1/256
111 pppqqqqqqq - rrrrrrr 0-1023 1/128