Alesis QuadraSynth Plus manual General Midi, System Common Messages

MIDI Supplement: Appendix B

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 QuadraSynth Plus message to an Alesis D4 Drum Module won’t do anything, but the message will be understood by other QuadraSynth 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 QuadraSynth 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 QuadraSynth 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 QuadraSynth 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

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