Alesis S4 MIDI S

APPENDIX B: MIDI Supplement

QuadraSynth Reference Manual 125

MIDI SUPPLEMENT

Most current electronic instruments and signal processors, including the

QuadraSynth, contain an internal computer. Computers and music have been

working together for decades, which is not surprising considering musicÕs

mathematical basis (consider frequencies, harmonics, vibrato rates, tunings, etc.). In

the mid-70s, microcomputers became inexpensive enough to be built into consumer-

priced musical instruments. They were used for everything from sound generation to

storing parameters in memory for later recall.

In 1983, the MIDI (Musical Instrument Digital Interface) specification was introduced

to better exploit the computers inside these new musical instruments, primarily to

ensure compatibility of equipment between manufacturers. MIDI expresses musical

events (notes played, vibrato, dynamics, tempo, etc.) as a common ÒlanguageÓ

consisting of standardized digital data. This data can be understood by MIDI-

compatible computers and computer-based musical instruments.

Before electronics, music was expressed exclusively as written symbols. By

translating musical parameters into digital data, MIDI can express not only the types

of musical events written into sheet music, but other parameters as well (such as

amount of pitch bend or degree of vibrato).

MIDI-compatible devices usually include both MIDI In and MIDI Out jacks, which

terminate in 5-pin DIN-style connectors. The MIDI Out jack transmits MIDI data to

another MIDI device. As you play a MIDI controller such as a keyboard, data

corresponding to what you play exits the MIDI Out jack. Example: If you play

middle C, the MIDI Out transmits a piece of data that says Òmiddle C is down.Ó If

you release that key, the MIDI Out transmits another piece of data that says Òmiddle

C has been released.Ó

If the keyboard responds to the dynamics of your playing, the note data will include

dynamics information too. Moving the modulation wheels and pedals attached to

many synthesizers will also generate data associated with the wheel or pedal being

used.

The MIDI In jack receives data from another MIDI device. In addition to the type of

performance data described above, rhythmically-oriented MIDI devices (e.g., drum

machines) can often transmit and/or receive additional MIDI timing messages that

keep other rhythmically-oriented units in a system synchronized with each other.

An optional MIDI Thru jack provides a duplicate of the signal at the MIDI In jack.

This is handy if you want to route MIDI data appearing at one device to another

device as well.