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Appendix B: MIDI Supplement
System Common Messages
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 Sys Ex 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 S4 Plus message to an
Alesis D4 Drum Module won't do anything, but the message will be understood by
other S4 Plus. 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.
General MIDI
General MIDI is an extension of the MIDI standard designed to meet the demands of
the ever-growing multimedia industry, and to make simple the act of playing
commercially produced MIDI sequences. The General MIDI standard utilizes all 16
channels available in MIDI. The S4 Plus is a perfect General MIDI companion, since
its Mix Mode uses 16 channels. Although many channels are commonly used for
specific types of instruments ( Example: Channel 1 is usually piano, channel 2 is
usually bass, etc.), channel 10 is always used for drums.
General MIDI also standardizes the placement of sound types in a sound device's
memory bank. The S4 Plus' Preset 4 Bank is designed specifically for General MIDI,
and organizes it sounds according to the General MIDI specification. This means,
when a sequencer sends a MIDI program change message that is supposed to call
up a particular sound, the correct sound on the S4 Plus will be called up, even if the
composer of the sequence used a different sound device. The Programs in Preset
Bank 4 use the General MIDI names (in some cases abreviated) with the letters GM
added to indicate their are designed specifically for use in General MIDI mode.
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S4 Plus Reference Manual
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