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APPENDIX B: MIDI Supplement
128 QuadraSynth Reference Manual
System Common Messages
Intended for all units in a system, some of these MIDI messages are:
Song Position Pointer. This indicates how many ÒMIDI beatsÓ (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 Sys-Ex for short) is considered ÒexclusiveÓ
because different manufacturers send and receive data over MIDI which is intended
only for that manufacturerÕs equipment. Example: Sending a QuadraSynth message to
an Alesis D4 Drum Module wonÕt do anything, but the message will be understood
by other QuadraSynths. 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 theyÕve 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.
(This appendix is an abridged version 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.)