System Common Messages - Alesis DM5 Reference Manual

Appendix B: MIDI Supplement
S
YSTEM
Intended for all units in a system, some of these MIDI messages are:
Song Position Pointer. This indicates how many "MIDI beats" (normally a 16th
note) have elapsed since a piece started (up to 16,384 total beats). It is primarily used
to allow different sequencers and drum machines to auto-locate to each other so that
if you start one sequencer, the other device will automatically jump to the same place
in the song, whereupon both continue on together.
System Exclusive. This message (called SysEx for short) is considered "exclusive"
because different manufacturers send and receive data over MIDI which is intended
only for that manufacturer's equipment. Example: Sending a DM5 message to an
Alesis QS6 Synthesizer won't do anything, but the message will be understood by
another DM5. This data often contains information about individual instrument
programs.
Timing Clock. A master tempo source (such as a sequencer) emits 24 timing
messages (clocks) per quarter note. Each device synchronized to the sequencer
advances by 1/24th of a quarter note when it receives the clock message, thus
keeping units in sync after they've both started at the same time. Many devices
subdivide this clock signal internally for higher resolution (e.g., 96 pulses per quarter
note).
Start. Signals all rhythmically-based units when to start playing.
Stop. Signals all rhythmically-based units when to stop playing.
Continue. Unlike a Start command, which re-starts a sequencer or drum machine
from the beginning of a song each time it occurs, sending a continue message after
stop will re-start units from where they were stopped.
(Portions of this appendix are abridged versions of material from Power Sequencing
with Master Tracks Pro/Pro 4 and The Complete Guide to the Alesis HR-16 and
MMT-8, copyright 1990 and 1989 respectively by AMSCO Publications, and is
adapted with permission.)
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OMMON ESSAGES
DM5 Reference Manual